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Ecology
Topic 5.1, 5.2, 5.3
Option G1, G2, G3, G4, and G5
Ecology
 Ecology is the study of how organisms interact with their
environment and each other.
• This interaction of organisms is a two-way interaction. Organisms are
affected by their environment, but by their activities they also change
the environment.
Levels of Organization
• Ecology is studied on several levels:
– Organism
• Ecologists may examine how one kind of organism meets the challenges of its environment,
either through its physiology or behavior.
– Population
• Group of individuals of the same species living in a particular geographic area.
– Community
• Consists of all the populations of different species that inhabit a particular area.
– Ecosystem
• Includes all forms of life in a certain area and all the nonliving factors as well.
– Biosphere
• The global ecosystem; the sum of all the planet’s ecosystems.
• Most complex level in ecology, including the atmosphere to an altitude of several
kilometers, the land down to and including water-bearing rocks under 3,000 m under
Earth’s surface, lakes and streams, caves, and the oceans to a depth of several kilometers.
• It is self contained, or closed, except that its photosynthesizers derive energy from sunlight,
and it loses heat to space.
Levels of Organization
Abiotic vs. Biotic
 Abiotic components
 Temperature, forms of energy, water, inorganic nutrients, and
other chemicals.
 Biotic components
 Organisms making up the community
Habitat
 Habitat The specific environment in which an organism lives in.
 Each habitat can be described by characteristic abiotic factors.
Abiotic Factors
 Physical and chemical factors (abiotic) affecting the
organisms living in a particular ecosystem:
 Solar energy
 Water
 Temperature
 Wind
 Soil composition
 Unpredictable disturbances
Abiotic Factors- Solar Energy
 Powers nearly all terrestrial and shallow-water
ecosystems.
 In aquatic environments that sunlight reaches,
the availability of light has a significant effect
on the growth and distribution of
photosynthetic bacteria and algae.
 Most photosynthesis occurs near the surface of
a body of water.
 In terrestrial environments, light is often not
the most important factor limiting plant
growth.
 In many forests, however, shading by trees
creates intense competition for light at ground
level.
Abiotic Factors- Water
 Essential to all life.
 Aquatic organisms have a seemingly
unlimited supply of water, but they face
problems of water balance if their own
solute concentrations does not match that
of their surroundings.
 These organisms confront solute conc. in
freshwater lakes and streams that are very
different from those in the sea.
 For a terrestrial organism, the main water
problem is the threat of drying out.
 Many land species have watertight coverings
that reduce water loss.
 Most terrestrial animals have kidneys that
save water by excreting very concentrated
urine.
Abiotic Factors- Temperature
 An important abiotic factor because of its effect on metabolism.
 Few organisms can maintain a sufficient active metabolism at
temperatures close to 0 degrees Celsius, and temperatures above 45
degrees Celsius destroy the enzymes of most organisms.
 Extraordinary adaptations enable some species to live outside this
temperature range.
 For example, some of the frogs and turtles living the northern United
States and Canada can freeze during winter months and still survive,
and bacteria living in hydrothermal vents and hot springs have enzymes
that function optimally at extremely high temperatures.
 Mammals and birds can remain considerably warmer than their
surroundings and can be active in a fairly wide range of temperatures,
but even these animals function best at certain temperatures.
Abiotic Factors- Wind
 An important abiotic factor for several reasons. Local wind damage
often creates openings in forests, contributing to patchiness in
ecosystems.
 Wind also increases an organism’s rate of water loss by
evaporation.
 The resulting increase in evaporative cooling can be advantageous on a
hot summer day, but it can cause dangerous wind chill in the winter.
Abiotic Factors- Soil composition
 Most soils are complex combinations of inorganic nutrients,
organic materials in various stages of decomposition, water, and
air.
 Such variables as soil structures, pH, and nutrient content often
play major roles in determining the distribution of organisms.
Abiotic Factors- Unpredicatable
disturbances
 Include fires, hurricanes, tornadoes, tsunamis, and volcanic
eruptions.
 Fire occurs frequently enough in some communities,
however, that many plants have adapted to this periodic
disturbance.
Natural Selection and Abiotic Factors
 Organisms are adapted to abiotic and biotic factors by natural
selection.
 An organism’s ability to survive and reproduce in a particular
environment is a result of natural selection.
 By eliminating the least fit individuals in populations,
environmental forces help adapt species to the mix of abiotic and
biotic factors that they encounter.
 The presence of a species in a particular place can come about it
two ways:
 The species may evolve in that location.
 The species may disperse to that location and be able to survive.
Biomes
 Biomes- A large ecosystem that is usually determined by
climate and categorized by the available producers and other
organisms that adapted to the particular environment.
 The major terrestrial biomes are named after the climatic
conditions and the vegetation, however, their microbial
organisms, fungi, and animals are also important.
 Climatograms
 Used to compare the annual precipitation and annual
temperature in various biomes.
Biomes
Biomes- Tropical Rainforest
 Temperature is warm all year long and has about 11-12 hours of
sunlight.
 Plenty of rain (200-400 cm per year) results in fast
decomposition, as a result the soil is very thin.
 Very complex species diversity
 Vegetation includes trees, vines, and epiphytes. Very rich animal
diversity.
Biomes- Shrublands (savanna,
chaparral)
 Lower rainfall (30-50 cm a year) and warm temperatures year
round.
 The plants are fire adapted because of the frequent fires.
 Typical plants are grasses with scattered trees and shrubs.
 Grazing animals, insects, birds, large predators.
Biomes- Deserts
 Very dry areas with less than 2 cm of yearly rainfall, very large
temperature fluctuations.
 They can grow some deep rooted shrubs, cacti, and other
succulent plants, annual plants with very fast growing period
 Adaptations to extreme dry conditions.
Biomes- Temperate Deciduous Forests
 Warm summers, cold winters.
 Fairly even annual rainfall (60-150 cm)
 Dominant species are various broad leaf trees, such as oak, maple,
hickory, birch, etch.
 Various shrubs and annuals are found in the broad leaf regions.
Biomes- Taiga
 Long, cold winters and short, wet summers that are sometimes
warm.
 Soil is acidic and nutrient-poor, not fit for many plants.
Biomes- Tundra
 Bitter cold winters, high winds and low precipitation (15-25 cm).
 Because the soil is constantly frozen, the temperatures are low and the
evaporation is also low, the soil is constantly saturated with water.
 Vegetation includes dwarf shrubs, grasses, mosses, and lichens.
 Characterized by permafrost, continuously frozen subsoil.
Community
 A biological community is an assemblage of all the populations
of organisms living close enough together for potential
interaction.
 Key characteristics of a community:
 1.Species diversity
 2.Dominant species
 3.Response to disturbances
 4.Trophic structure
 5. Community interactions
Community
 1.Species diversity
 The variety of different kinds of organisms that make it up,
 Has two components:
 1. species richness
The total number of different species in the community.
 The more species present in a sample, the 'richer' the sample.
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Species richness as a measure on its own takes no account of the number of individuals of each
species present. It gives as much weight to those species which have very few individuals as to
those which have many individuals. Thus, one daisy has as much influence on the richness of an
area as 1000 buttercups.
 2. species abundance (sometimes referred to as “evenness”)
 a measure of the relative abundance of the different species making up the richness of
an area.
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To give an example, we might have sampled two different fields for wildflowers. The sample from
the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from
the second field comprises 20 daisies, 49 dandelions and 931 buttercups (see the table below).
Both samples have the same richness (3 species) and the same total number of individuals (1000).
However, the first sample has more evenness than the second. This is because the total number of
individuals in the sample is quite evenly distributed between the three species. In the second
sample, most of the individuals are buttercups, with only a few daisies and dandelions present.
Sample 2 is therefore considered to be less diverse than sample 1.
Community
 1.Species diversity (continued)
 A community dominated by one or two species is considered to be
less diverse than one in which several different species have a similar
abundance.
 As species richness and evenness increase, so diversity increases.
 Simpson's Diversity Index is a measure of diversity which takes
into account both richness and evenness.
 n = the total number of organisms of a particular species
 N = the total number of organisms of all species
 The value of D ranges between 0 and 1. With this index, 1
represents infinite diversity and 0, no diversity.
 http://geographyfieldwork.com/Simpson'sDiversityIndex.htm
Community
 2.Dominant species
 In general, a small number of species exert strong control over a
community’s composition and diversity.
 In terrestrial situations, the dominant species is usually the most
prevalent form of vegetation.
 For example, wildflowers are the dominant species in some communities.
 The types and structural features of plants largely determine the kinds of animals
that live in a community.
 Keystone species is a species that exerts strong control on
community structure because of its ecological role, or niche.
 For example, a seastar of the genus Pisaster is a keystone predator that reduces the
density of the strongest competitors in the community, thus preventing the
competitive exclusion of weaker competitors.
 In an experiment on the Washington coast, Pisaster was removed from the
community. The results was that the Pisaster’s main prey, a mussel of the genus
Mytillus, outcompeted many of the other shoreline organisms reducing the
number of organisms from over 15 species to under 5 species.
Community
Community
 2.Dominant species (continued…)
 Keystone species (continued…)
 Also, sea otters are a keystone predator in the North Pacific. Sea otters feed on
sea urchins, and sea urchins feed mainly on kelp, a large seaweed. In areas where
sea otters are abundant, sea urchins are rare and kelp forests are well developed.
Where sea otters are rare, sea urchins are common and kelp is almost absent.
 During the last 20 years, sea otters have declined dramatically in large areas
off the coast of western Alaska. The loss of this keystone species has allowed
sea urchin populations to increase, resulting in the destruction of kelp forests.
 Killer whales are the cause of the sea otter decline, which is probably because
the previous prey of the whales, mainly seals and sea lions, have declined in
density.
 The decline of these prey species reflects a decline in the populations of fish
species that the seals and sea lions eat.
 And, all of these changes in the Alaskan marine communities are probably
related to human overfishing in the North Pacific
Community
Community
 3. Response to Disturbances
 Events such as storms, fire, floods, droughts, overgrazing, or human activity that damage
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biological communities, remove organisms from them, and alter the availability of resources.
The types of disturbances and their frequency and severity vary from community to
community.
Small-scale disturbance often have positive effects. For example, when a large tree falls in a
windstorm, it disturbs the immediate surroundings, but it also creates new habitats.
For instance, more light may now reach the forest floor, giving small seedlings the
opportunity to grow; or the depression left by its roots may fill with water and be used as
egg-laying sites by frogs, salamanders, and numerous insects. Small-scale disturbances may
enhance environmental patchiness, which can contribute to species diversity in a community.
Communities change drastically following a severe disturbance that strips away vegetation
and even soil. The disturbed area may be colonized by a variety of species, which are
gradually replaced by a succession of other species, in a process called ecological
succession.
Community
 3. Response to Disturbance (continued)…
 Early successional communities are characterized by a low species
diversity, simple structure and broad niches
 The succession proceeds in stages until the formation of a climax
community.
 The most stable community in the given environment until some disturbance
occurs.
 Two types of Ecological Succesion:
 Primary Succession
 Secondary Succession
Community
 3. Response to Disturbances (continued…)
 Primary succession
 When ecological succession begins in a virtually lifeless area with no soil.
 Usually takes hundreds or thousands of years.
 For example, new volcanic islands or rubble left by a retreating glacier. Often the
only life-forms initially present are autotrophic bacteria. Lichens and mosses are
commonly the first large photosynthesizers to colonize the area. Soil develops
gradually as rocks weather and organic matter accumulates from the decomposed
remains of the early colonizers. Lichens and mosses are gradually overgrown by
grasses and shrubs that sprout from seeds blow in from nearby areas or carried in
by animals. Eventually, the area is colonized by plants that become the community’s
prevalent form of vegetations.
 Secondary succession
 Occurs when a disturbance has destroyed an existing community but left the soil
intact.
 For example, forested areas that are cleared for farming, areas impacted by fire or
floods.
Community
 3. Response to Disturbances (continued…)
 Primary Succession
 Example: autotrophic prokaryoteslichens,
mossesgrassesshrubstreesclimax communty
 Secondary Succession
 Example: herbaceous plants woody shrubs trees climax community
Community
 4. Trophic structure
 The feeding relationships among the various species making up the
community.
 A community’s trophic structure determines the passage of energy
and nutrients from plants and other photosynthetic organisms to
herbivores and then to carnivores.
 The sequence of food transfer up the trophic levels is known as a
food chain
 Trophic levels are arranged vertically, and the names of the levels appear in
colored boxes.
 The arrows connecting the organisms point from the food to consumer. This
transfer of food moves chemical nutrients and energy from the producers up
though the trophic levels in a community.
Community
 4. Trophic Structure (continued…)
 At the bottom, the trophic level that supports all others consists of
autotrophs, called producers.
 Photosynthetic producers use light energy to power the synthesis of organic
compounds. Plants are the main producers on land. In water, the producers are
mainly photosynthetic protists and cyanobacteria, collectively called
phytoplankton. Multicellular algae and aquatic plants are also important
producers in shallow waters.
 All organisms in trophic levels about the producers are heterotrophs,
or consumers, and all consumers are directly or indirectly
dependent on the output of producers.
Community
 4.Trophic Structure (continued…)
 Trophic Levels:
 Primary producers
 Mostly photosynthetic plants or algae
 Primary consumers
 Herbivores, which eat plants, algae, or phytoplankton.
 On land include grasshoppers and many insects, snails, and certain vertebrates
like grazing mammals and birds that eat seeds and fruits
 aquatic environments include a variety of zooplankton (mainly protists and
microscopic animals such as small shrimp) that eat phytoplankton.
 Secondary consumers
 Include many small mammals, such as a mouse, a great variety of small birds,
frogs, and spiders, as well as lions and other large carnivores that eat grazers.
 In aquatic ecosystems, mainly small fishes that eat zooplankton
 Tertiary consumers
 Snakes that eat mice and other secondary consumers.
 Quaternary consumers
 Include hawks in terrestrial environments and killer whales in marine environment.
Community
 4.Trophic Structure (continued…)
 Another trophic level of consumers are called detrivores which derive their energy
from detritus, the dead material produced at all the trophic levels.
 Detritus includes animal wastes, plant litter, and all sorts of dead organisms.
 Most organic matter eventually becomes detritus and is consumed by
detritivores.
 A great variety of animals, often called scavengers, eat detritus. For instance,
earthworms, many rodents, and insects eat fallen leaves and other detritus.
Other scavengers include crayfish, catfish, crows, and vultures.
 A community’s main detritivores are the prokaryotes and fungi, also called
decomposers, or saprotrophs, which secrete enzymes that digest organic
material and then absorb the breakdown products.
 Enormous numbers of microscopic fungi and prokaryotes in the soil and in mud
at the bottom of lakes and oceans convert (recycle) most of the community’s
organic materials to inorganic compounds that plants or phytoplankton can use.
 The breakdown of organic materials to inorganic ones is called
decomposition.
Community
Community
 4.Trophic Structure (continued…)
 A more realistic view of the trophic structure of a community is a
food web, a network of interconnecting food chains.
 Food webs, like food chains, do not typically show detrivores, which
consume dead organic material from all trophic levels.
Community
 5. Community Interactions
 Interspecific competition:
 If two different species are competing for the same resource.
 Causes the growth of one or both populations may be inhibited.
 May play a major role in structuring a community.
 Weeds growing in a garden compete with garden plants for nutrients and water.
 Lynx and foxes compete for prey such as snowshoe hares in northern forests.
Community
 5. Community Interactions (continued…)
 Competitive exclusion principle
 In 1934, Russian ecologist Gause studied the effects of interspecific
competition in laboratory experiments with two closely related species
of Paramecium.
 Gause cultured these protists under stable conditions with a constant amount of
food added every day.
 When he grew the two species in separate cultures, each population grew rapidly
and then leveled off at what was apparently carrying capacity of the culture.
 But when Gause cultured the two species together, one species was driven to
extinction.
 Gause concluded that two species so similar that they compete the
same limited resources cannot coexist in the same place. One will use
the resources more efficiently and thus reproduce more rapidly than
the other. Even a slight reproductive advantage will eventually lead to
local elimination of the inferior competitor.
Community
 5. Community Interactions (continued…)
 The competitive exclusion principle applies to what is called a
species’ niche.
 In ecology, a niche is a species’ role in its community, or the sum total of its use
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of the biotic and abiotic resources of its habitat.
For example, the attachment sites on intertidal rocks, the amount of exposure to
seawater and air, and the food it consumes are some of the aspects of each
barnacle’s niche.
The fundamental niche of a species includes the total range of environmental
conditions that are suitable for existence without the influence of interspecific
competition or predation from other species.
The realized niche of a species is the actual mode of existence, which results
from its adaptations and competition with other species.
Combining the niche concept with the competitive exclusion principle, we
might predict that two species cannot coexist in a community if their niches are
identical.
 Figure 9g-1: The following diagram shows a hypothetical
situation where a species distribution is controlled by just
two environmental variables: temperature and moisture. The
green and yellow areas describe the combinations of
temperature and moisture that the species requires for
survival and reproduction in its habitat. This resource space
is known as the fundamental niche. The green area describes
the actual combinations of these two variables that the
species utilizes in its habitat. This subset of the fundamental
niche is known as the realized niche.
Community
 5. Community Interactions (continued…)
 There are two possible outcomes of competition between
species having identical niches: Either the less competitive
species will be driven to local extinction, or one of the species
may evolve enough through natural selection to use a different
set of resources.
 This differentiation of niches that enables similar species to coexist in a
community is called resource partioning.
 It is a way in which different species can use the same resource, such
as food, without occupying the same physical location at the same
point in time.
 For example, different warblers eat the same caterpillar, but they
occupy different positions in the tree. Two primarily occupy the area
near the trunk, with the others share the edges of the branches, but at
different heights. The result is the warblers do not overtly compete
for food in the same space.
Community
 5. Community Interactions (continued…)
 Predation is an interaction between species in which one species,
the predator, kills and eats another, the prey.
 Because eating and avoiding being eaten are prerequisites to
reproductive success, the adaptations of both predators and prey tend
to be refined through natural selection.
 Examples of prey capturing strategies:
 Most predators have acute senses enable them to locate prey.
 In addition, adaptations such as claws, teeth, fangs, stingers, or poisons
help catch and subdue prey.
 Predators are generally fast and agile, whereas those that lie in ambush are
often camouflaged in their environments.
 Predators may also use mimicry; some snapping turtles have a tongue that
resembles a wriggling worm, thus luring small fish.
Community
Camouflage
Chemical Defense
Community
 5. Community Interactions (continued…)
 Predator defenses:
 Mechanical defenses: such as the porcupine’s sharp quills or the hard shells of
clams and oysters.
 Chemical defenses: animals are often bright colored, a warning to predators; like
a poison arrow-frog or a skunk.
 Batesian mimicry: a palatable or harmless species mimics an unpalatable or
harmful one; like the king snake mimics the poisonous coral snake
 Mullerian mimicry: two unpalatable species that inhabit the same community
mimic each other; like bees and wasps
Mullerian Mimicry
Batesian Mimicry
Community
 5. Community Interactions (continued…)
 Herbivory
 Animals that eat plants or algae
 Aquatic herbivores include sea urchins, snails, and some fishes.
 Terrestrial herbivores include cattle, sheep, and deer, and small insects.
 Herbivorous insects may locate food by using chemical sensors on their feet,
and their mouthparts are adapted for shredding tough vegetation or sucking
plant juices.
 Herbivorous vertebrates may have specialized teeth or digestive systems
adapted for processing vegetation. They may also use their sense of smell to
identify food plants.
 Because plants cannot run away from herbivores, chemical toxins, often in
combination with various kinds of anti-predator spines and thorns, are their
main weapons against being eaten.
Community
 5. Community Interactions (continued…)
 Herbivory
 Some herbivore-plant interactions illustrate the concept of coevolution, a series of
reciprocal evolutionary adaptations in two species.
 Coevolution occurs when a change in one species acts as a new selective force
on another species, and counteradaptation of the second species in turn affects
the selection of individuals in the first species.
 For example: an herbivorous insect (the caterpillar of the butterfly Heliconius,
top left) and a plant (the passionflower Passiflora, a tropical vine). Passiflora
produces toxic chemicals that protect its leaves from most insects, but
Heliconius caterpillars have digestive enzymes that break down the toxins. As a
result, Heliconius gains access to a food source that few other insects can eat.
o The Passiflora plants have evolved defenses against the Heliconius insect. The
leaves of the plant produce yellow sugar deposits that look like Heliconius
eggs. Therefore, female butterflies avoid laying their eggs on the leaves to
ensure that only a few caterpillars will hatch and feed on any one leaf.
Because of this, the Passiflora species with the yellow deposits are less likely
to be eaten.
Community
Passiflora
Community
 5. Community Interactions (continued…)
 Symbiotic Relationships are interactions between two or more
species that live together in direct contact.
 Three main types:
 Parasitism
 Commensalism
 Mutualism
 *Parasitism and mutualism can be key factors in community
structure.
Community
 5. Community Interactions (continued…)
 Parasitism
 A parasite lives on or in its host and obtains its nourishment from the host.
 For example: A tapeworm is an internal parasite that lives inside the intestines of
a larger animal and absorbs nutrients from its hosts.
 Another example: Ticks, which suck blood from animals, and aphids, which tap
into the sap of plants, are examples of external parasites.
 Natural selection favors the parasites that are best able to find and feed on hosts.
 Natural selection also favors the evolution of host defenses.
 For example, the immune system of vertebrates provides a multiprolonged
defense against specific internal parasites. With natural selection working on
both host and parasite, the eventual outcome is often a relatively stable
relationship in which the host is not usually killed.
Tapeworm in small intestine
Tick on dog
Community
 5. Community Interactions (continued…)
 Commensalism
 One partner benefits without significantly affecting the other.
 Few cases of absolute commensalism have been documented, because it is unlikely that
one partner will be completely unaffected.
 For example: algae that grow on the shells of sea turtles, barnacles that attach to whales,
and birds that feed on insects flushed out of the grass by grazing cattle.
Algae on Sea Turtle
Barnacles on Whale
Community
 5. Community Interactions (continued…)
 Mutualism
 Benefits both partners in the relationship.
 For example: the association of legume plants and nitrogen-fixing bacteria.
Bacteria turn nitrogen in the air to nitrates that the plants can use
 Another example: Acacia trees and the predaceous ants they attract.
 Tree provides room and board for ants
 Ants benefit the tree by attacking virtually anything that touches it.
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Acacia Trees and Ants
Ecosystems
 An ecosystem consists of all the organisms in a community as well as the abiotic
environment with which the organisms interact.
 Ecosystems can range from a microcosm such as a terrarium to a large area such as a
forest.
 Regardless of an ecosystem’s size, its dynamics involve two processes- energy flow
and chemical cycling.
 Energy flow: the passage of energy through the components of the ecosystem.
 For most ecosystems, the sun is the energy source, but exceptions include several
unusual kinds of ecosystems powered by chemical energy obtained from inorganic
compounds.
 For example, an a terrarium, energy enters in the form of sunlight.
 Plants (producers) convert the light energy to chemical energy.
 Animals (consumers) take in some of this chemical energy in the form of organic compounds when
they eat the plants.
 Detrivores, such as bacteria and fungi in the soil, obtain chemical energy when they decompose the
dead remains of plants and animals.
 Every use of chemical energy by organisms involves a loss of some energy to the surroundings in the
form of heat.
 Eventually, therefore, the ecosystem would run out of energy if it were not powered by a continuous
inflow of energy from an outside source.
Ecosystems
Ecosystems
 Chemical cycling: involves the transfer of materials within the
ecosystem.
 An ecosystem is more or less self-contained in terms of matter.
 Chemical elements such as carbon and nitrogen are cycled between
abiotic components (air, water, and soil) and biotic components of
the ecosystem.
 The plants acquire these elements in inorganic form from the air and
soil and fix them into organic molecules, some of which animals
consume.
 Detrivores return most of the elements in inorganic form to the soil
and air.
 Some elements are also returned as the by-products of plant and
animal metabolism.
Ecosystems
Ecosystems
 Biomass is the term ecologist use to refer to the amount, or mass,
of living organic material in an ecosystem.
 Primary production is the amount of solar energy converted to
chemical energy (organic compounds) by an ecosystem’s producers
for a given area and during a give time period.
 It can be expressed in units of energy or of mass.
 The primary production of the entire biosphere is 170 billion tons of
biomass per year.
 Different ecosystems vary considerably in their primary production as
well as in their contribution to the total production of the biosphere.
 Net primary production refers to the amount of biomass produced
minus the amount used by producers as fuel for their own cellular
respiration.
 Gross production- respiration = net production (GP-R=NP)
Ecosystems
•Tropical rainforests are
among the most
productive terrestrial
ecosystems and
contribute a large portion
of the planet’s overall
production of biomass.
•Coral reefs also have
very high production, but
their contribution to global
production is small
because they cover such
a small area.
•Even though the open
ocean has very low
production, it
contributes the most to
Earth’s total net primary
production because of
its huge size- it covers
65% of Earth’s surface
Ecosystems
 Pyramid of Production
 Illustrates the cumulative loss of energy with each transfer in a food
chain.
 Each tier of the pyramid represents one trophic level, and the width of
each tier indicates how much of the chemical energy of the tier below
is actually incorported into the organic matter of that trophic level.
 Note that producers convert only about 1% of the energy in the
sunlight available to them to primary production.
 In this idealized pyramid, 10% of the energy available at each trophic
level becomes incorporated into the next higher level.
 The efficiencies of energy transfer usually range from 5 to 20%.
 In other words, 80 to 95% of the energy at one trophic level never
transfers to the next.
Ecosystems
Ecosystems
 Pyramid of Production
 An important implication of the stepwise decline of energy in a
trophic structure is that the amount of energy available to top-level
consumers is small compared with that available to lower-level
consumers.
 Only a tiny fraction of the energy stored by photosynthesis flows
through a food chain to a tertiary consumer, such as a snake feeding
on a mouse.
 This explains why top-level consumers such as lions and hawks
require so much geographic territory; it takes a lot of vegetation to
support trophic levels so many steps removed from photosynthetic
production.
 This also explains why there is less biomass and fewer numbers of
organisms in higher trophic levels.
Ecosystems
 Life depends on the recycling of chemicals. Because chemical
cycles involve both biotic and abiotic components, they are called
biogeochemical cycles.
 General scheme for the cycling of a nutrient within an ecosystem:
 1. Producers incorporate chemicals from the abiotic reservoir into
organic compounds.
 2. Consumers feed on the producers, incorporating some of the
chemicals into their own bodies.
 3. Both producers and consumers release some chemicals back to the
environment in waster products (CO2 and nitrogen wastes of
animals).
 4. Detritivores play a central role. As organisms die, these
decomposers return chemicals in inorganic form to the soil, water,
and air. The producers gain a renewed supply of raw materials, and
the cycle continues.
Ecosystems
 Biogeochemical cycles:
 Water cycle
 Carbon cycle
 Nitrogen cycle
 Phosphorous cycle
Ecosystems
 Carbon cycle:
 Carbon is the major ingredient of all organic molecules. Like water, the element
carbon has an atmospheric reservoir and cycles globally. Other abiotic reservoirs
of carbon include fossil fuels, dissolved carbon compounds in the oceans, and
sedimentary rocks such as limestone.
 The reciprocal metabolic processes of photosynthesis and cellular respiration are
mainly responsible for the cycle of carbon between the biotic and abiotic worlds.
 Carbon compounds in detritus-animal wastes, plant litter, and dead organisms of
all kinds—are consumed and decomposed by detrivores, and detritivore
respiration, along with that of plants, animals, and other organisms, returns CO2
to the atmosphere.
 On a global scale, the return of CO2 to the atmosphere by respiration closely
balances its removal by photosynthesis. However, the increased burning of wood
and fossil fuels (coal and petroleum) is raising the level of CO2 in the atmosphere.
This is appears to be leading to the significant problem of global warming.
Ecosystems
The Greenhouse Effect
 Greenhouse Effect: a natural phenomenon caused by the release




of greenhouse gases, which act as a thermal blanket in the
atmosphere, letting in sunlight, but trapping the heat that would
normally radiate back into space
About 75% of the natural greenhouse effect is due to water vapor.
The next most significant contributor is carbon dioxide.
In the past, our climate has shifted between periods of stable
warm conditions to cycles of ice ages and “interglacials.”
The current period of warming is explained in part by recovery
after the last ice age 10,000 years ago. However there are many
indications that climate warming is accelerting and that this
acceleration is partly the result of human activity, in particular, the
release of greenhouse gases into the atmosphere.
The Greenhouse Effect
 Sources of Greenhouse Gases:
 Carbon dioxide
 Exhaust from cars, combustion of coal, wood, oil, and burning rainforests
 Methane
 Plant debris and growing vegetation, bleching and flatus of cows
 Chloro-fluoro-carbons (CFCs)
 Leaking coolant from refrigerators and air conditioners
 Nitrous oxide
 Car exhaust
 Tropospheric ozone (found in the lower atmosphere)
 Triggered by car exhaust (smog)
The Greenhouse Effect
 What are the consequences?
 Recent data from the UN Environment Programme, based on
studies of glaciers across nine mountain ranges, indicates that
average glacial shrinkage is accelerating.
 Moreover, the rates of summer melting of Arctic ice are
exceeding early predictions, leading to new forecasts predicting
an ice-free Arctic by as early as 2013.
 Ice sheet shrinkage has a feedback effect too, because ice
increases the amount of heat reflected back from the Earth.
 The effect of global warming on the Earth’s systems is likely to
be considerable.
The Greenhouse Effect
 Potential Effects of Global Warming
 Sea levels
 Expected to rise by 50 cm by the year 2100
 Result of the thermal expansion of ocean water and melting glaciers and ice
shelves.
 Warming may also expand habitat for many pests, e.g. mosquitoes, shifting the
range of infectious disease.
 Forests
 Higher temps and precipitation changes could increase forest susceptibility to
fire, disease, and insect damage.
 Forest fires release more carbon into the atmosphere and reduces the size of
carbon sinks.
 A richer CO2 atmosphere will reduce transpiration in plants.
 Weather patterns
 May cause regional changes in weather patterns such as El Nino and La Nina, as
well as affecting the intensity and frequency of storms. Driven by higher ocean
surface temperatures, high intensity hurricanes no occur more frequently.
The Greenhouse Effect
 Water resources
 Changes in precipitation and increased evaporation will affect the water
availability for irrigation, industrial use, drinking, and electricity generation.
 Agriculture
 Climate change may threaten the viability of important crop-growing regions.
 Paradoxically, climate change can cause both too much and too little rain.
 The ice-albedo effect
 Ice has a stabilizing effect on global climate, reflecting nearly all the sun’s energy
that hits it.
 As polar ice melts, more of that energy is absorbed by the Earth.
The Greenhouse Effect
 The Precautionary Principle
 states that if an action or policy has a suspected risk of causing harm to
the public or to the environment, in the absence of scientific
consensus that the action or policy is harmful, the burden of proof
that it is not harmful falls on those taking the action.
 allows policy makers to make discretionary decisions in situations
where there is the possibility of harm from taking a particular course
or making a certain decision when extensive scientific knowledge on
the matter is lacking.
 implies that there is a social responsibility to protect the public from
exposure to harm, when scientific investigation has found a plausible
risk.
 These protections can be relaxed only if further scientific findings
emerge that provide sound evidence that no harm will result.
The Greenhouse Effect
 The Precautionary Principle (continued):
 “In order to protect the environment, the precautionary approach
shall be widely applied by States according to their capabilities.
Where there are threats of serious or irreversible damage, lack of
full scientific certainty shall not be used as a reason for postponing
cost-effective measures to prevent environmental
degradation”~United Nations Conference on Environment
and Development
 Should the health and wealth of future human generations be
jeopardized?
 Is it right to knowingly damage the habitat of, and possibly drive to
extinction, species other than humans?
Populations
 Population: a group of individuals of a single species that
occupy the same general area.
 These individuals rely on the same resources, are influenced by the
same environmental factors, and have a high likelihood of interacting
and breeding with one another.
 Most of our knowledge of population dynamics comes from studies
of much smaller groups that are confined by more restricted
geographic boundaries—for instance, a population of binds on an
island, or fish in a lake, or protists in a laboratory culture.
Populations
 Population density is the number of individuals of a species per
unit area or volume. For example, the number of oak trees per
square kilometer (km2) in a forest, or the number of earthworms
per cubic meter (m3) in forest soil.
 To measure population density, ecologists use a variety of
sampling techniques to estimate population densities. In most
cases, it is impractical or impossible to count all individuals of a
population.
 Sampling Techniques:
 Point Sampling
 Transect Sampling
 Quadrat Sampling
 Mark and recapture (capture-recapture)
Populations
 Mark and recapture (capture-recapture)
 Animals are captured, marked, and then released. After a suitable
time period, the population is resampled. The number of marked
animals recaptured in a second sample is recorded as a proportion
of the total.
 Useful for: determining total population density for highly mobile species in
a certain area (e.g. butterflies). Movements of individuals in the population can
be tracked (especially when used in conjunction with electronic tracking
devices).
 Considerations: time consuming to do well. Not suitable for immobile
species. Population should have a finite boundary. Period between samplings
must allow for redistribution of marked animals in the population. Marking
should present little disturbance and should not affect behavior.
Populations
 Mark and recapture (capture-recapture) Steps:
 1. The population is sampled by capturing as many of the individuals as possible and




practical.
2. Each animal is marked in a way to distinguish it from unmarked animals (unique
mark for each individual not required).
3. Return the animals to their habitat and leave them for a long enough period for
complete mixing with the rest of the population to take place.
4. Take another sample of the population (this does not need to be the same sample
size as the first sample, but it does have to be large enough to be valid).
5. Determine the numbers of marked to unmarked animals in the second sample.
Use the following equation (The Lincoln Index) to estimate the size of the overall
population:
 Population size= (n1 x n2)/n3
 n1= number of individuals initially caught, marked, and released
 n2=total number of individuals caught in the second sample
 n3= number of marked individuals in the second sample.
Populations
 Within a population’s geographic range, local densities may vary
greatly.
 The dispersion pattern of a population refers to the way
individuals are spaced within their area.
 These patterns are important characteristics for an ecologist to
study, since they provide insights into the environmental effects
and social interactions in the population.
 Clumped
 Uniform
 Random
Populations
 Clumped pattern
 Most common in nature
 Individuals are aggregated in patches
 Often results from an unequal distribution of resources in the
environment.
 For example, plants or fungi may be clumped in areas where soil conditions and
other factors favor germination and growth.
 Clumping of animals is often associated with uneven food distribution
or with mating or other social behavior.
 For example, fish are often clumped in schools, which may reduce predation
risks and increase feeding efficiency. Mosquitoes often swarm in great numbers,
increasing their chances for mating.
Populations
 Uniform, or even, pattern
 Pattern of dispersion often results from interactions between the
individuals of a population.
 For example, some plants secrete chemicals that inhibit the germination and
growth of nearby plants that could compete for resources.
 Animals may exhibit uniform dispersion as a result of territorial
behavior.
 For example, penguins and humans
Populations
 Random dispersion
 Individuals in a population are spaced in a patternless,
unpredictable way.
 For example, clams living in a coastal mudflat might be randomly dispersed at
times of the year when they are not breeding and when resources are plentiful
and do not affect their distribution.
 Varying habitat conditions and social interactions make random
dispersion rare.
Populations
 Population size
 The number of individuals comprising a population may fluctuate
over time. These changes make populations dynamic.
 A population in equilibrium has no net change in its abundance.
 Population Growth = B – D + I – E
• Factors that influence the number of individuals in a population:
– Birth (B) also known as natality
– Death (D) also known as mortality
– Immigration (I)
– Emigration (E)
Populations
 Life Tables
 Used to determine the average lifespan of various plants and animal
species to study the dynamics of population growth.
 http://www.ssa.gov/OACT/STATS/table4c6.html
 Survivorship curves
 Graphs generated from life tables to make the data easier to
comprehend.
 Plot the proportion of individuals alive at each age.
• Type 1- produce few offspring, take care of their young, many survive into
maturity.
• Type 2- intermediate, more constant mortality over the entire life span.
• Type 3- high death rates for the very young, mature individuals survive longer,
usually involves very large # of offspring with little or no parent care
Populations
Three types of survivorship curves
Populations
 The Exponential Growth Model
 The rate of population increase under ideal conditions.
(High Birth Rate, Low Death Rate)
 Gives an idealized picture of unregulated population
growth; no population can grow exponentially
indefinitely.
 The whole population multiplies by a constant factor
during each time interval.
 The simple equation G=rN describes this J-shaped curve
 G : growth rate of the population (the number of new individuals
added per time interval)
 N: stands for the population size (the number of individuals in the
population at a particular time)
 r: intrinsic rate of increase; remains constant (maximum capacity
of members that population to reproduce)
Populations
 Logistic Growth Model
 A description of idealized population growth that is slowed by
limiting factors as the population size increases.
 Limiting factors are environmental factors that restrict population
growth.
 G=rN(K-N)/K
 K= carrying capacity (maximum population size that a particular
environment can support or “carry”).
 S-shape curve
 1. Exponential Growth Phase-When the population first starts growing, N
is very small compared to the carrying capacity K. Population growth is close to
exponential growth; (K-N)/K nearly equals K/K or 1
 2. Transitional Phase- The population growth starts to slow; N gets closer to
carrying capacity, the term (K-N)/K becomes an increasingly smaller fraction.
 3. Plateau Phase- Carrying capacity is reached and the population is as big as
it can theoretically get in its environment; N=K, therefore (K-N)/N=0,
therefore G=O.
Populations
Logistic Growth Curves
Populations
 What does the logistic growth model suggest to us about real
populations in nature?
 Model predicts that a population’s growth rate will be small when
the population size is either small or large, and highest when the
population is at an intermediate level relative to the carrying
capacity.
 Small Population: resources are abundant, and the population is able to grow
nearly exponentially. The increase is small because N is small.
 Large Population: limiting factors strongly oppose the population’s potential to
increase. These limiting factors cause the birth rates to decrease, the death rate
to increase, or both. Eventually, the population stabilizes at the carrying
capacity (K), when the birth rate equals the death rate.
**It is important to realize that this is a mathematical model…no natural
populations fit perfectly!**
Populations
 Factors that appear to regulate growth in natural populations:
 Density-dependent factors:
 Competition among members of a growing population for limited resources,
like food or territory.
 Health of organisms
 Predation
 Physiological factors (reproduction, growth, hormone changes)
 Density independent factors
• Regardless of population density, these factors affect individuals to the same
extent.
– Weather conditions
– Acidity
– Salinity
– Fires
– Catastrophies
Populations
 Life History is the series of events from birth through
reproduction to death.
 For a given population in a particular environment, natural
selection will favor the combination of life history traits that
maximizes an individual’s output of viable, fertile offspring.
 Key life history traits:
 Age at which reproduction first occurs
 Frequency of reproduction
 Number of offspring
 Amount of parental care given.
Populations
 Life History (continued)
 Some ecologists hypothesize that different life history patterns are favored under
different population densities and conditions.
 r-selection (r-strategies)
 Individuals mature early
 produce a large number of offspring at a time. Usually only reproduce once.
 Have a small body size
 Have a short life span
 For example, insects and weeds
 K-selection (K-strategies)
 Typically larger-bodied
 Long life span, late maturity
 Reproduction occurs at a later age with the production of a few, well-cared for
offspring. Usually reproduce more than once.
 Common in populations that live at densities close to the carrying capacity (K) of
their environment.
 Example: many large terrestrial vertebrates
Populations
 Life history (continued)
 There are organisms that display either extreme r- or K- strategies,
but most organisms have life histories that are intermediate on the
continuum.
 Some organisms such as Drosophila switch strategies depending on
environmental conditions:
 In a predictable environment
In order to maximize fitness, it pays to invest resources in long-term
development and long life (K-strategy)
 In an unstable environment
 It is better to produce as many offspring as quickly as possible (r-strategy)
 *ecological disruption favors r-strategists such as pathogens and pest species

Impacts of Humans on Ecosystems
 Statospheric Ozone Depletion
 Loss of biodiversity
 Endangered Species
 Impact of Alien Species
 Fisheries Management
Impacts of Humans on Ecosystems
 Stratospheric Ozone Depletion
 Ozone (O3) is found in a band of the upper stratosphere as a
renewable thin veil.
 It absorbs about 99% of the harmful incoming UV radiation from the
sun and prevents it from reaching the Earth’s surface.
 An increase in UV-B radiation is likely to cause immune system
suppression in animals, lower crop yields, a decline in the
productivity of forests and surface dwelling plankton, more smog,
changes in the global climate, increasingly severe sunburns, increase
in skin cancers, and more cataracts of the eye.
 Ozone is being depleted by a handful of human-produced chemicals:
 CFCs appear to be the primary cause for ozone depletion. UV light hits a CFC
molecule and releases a chlorine atom. Chlorine reacts with ozone, forming a
Chlorine oxide molecule. This interferes with ozones ability to renew itself,
causing holes in the ozone layer.
Impacts of Humans on Ecosystems
Impacts of Humans on Ecosystems
 Loss of Biodiversity
 Biodiversity is measured by species. It is not distributed evenly on
Earth, being consistently richer in the tropics and concentrated more
in some areas than in others.
 Biodiversity hotspots are located in the tropics and most are forests.
 Loss of biodiversity reduces the stability and resilience of natural
ecosystems and decreases the ability of their communities to adapt to
changing environmental conditions.
Impacts of Humans on Ecosystems
 Endangered Species
 Species under threat of severe population loss or extinction are
classified as either endangered or threatened.
 An endangered species is one with so few individuals that it is at high
risk of local extinction, while a threatened (or vulnerable) species is
likely to become endangered in the near future.
 For example, hunting and collecting are one cause of species decline. Black
Rhinoceros were once plentiful throughout much of Africa. Now, only remnant
populations remain. In Kenya, 98% of the population was lost in only 17 years.
Conservationists suspect that a trader with a large stockpile of horn is trying to
cause rhinoceros extinction in order to increase the horn’s value. 
Impacts of Humans on Ecosystems
 Impact of Alien Species
 Alien species is a term used to describe those organisms that have
evolved at one place in the world and have been transported by
humans, either intentionally or in advertently, to another region.
 Some of these alien species are beneficial
 e.g. introduced agricultural plants and animals, and Japanenese clams and oysters
 Invasive species are those alien species that have a detrimental effect
on the ecosystems into which they have been imported.
 They number in their hundreds with varying degrees of undesirability to humans.
 Humans have brought in may exotic species into new environments for use as pets,
food, ornamental specimens or decoration, or through cargo shipments.
 Some have been deliberately introduced to control another pest species and have
themselves become a problem.
 The most destructive are aggressive plants, eg. Mile-a-minute weeda perennial
vine from Central and South America, miconiaa South American tree invading
Hawaii and Tahiti, and Caulerpa seaweedthe aquarium strain now found in the
Mediterranean.
Impact of Humans on Ecosystems
 The Impact of Alien Species (continued)
 An example of an alien species, and impact it had on ecosystem:
 The introduction of the brushtail possum into New Zealand, where it has
severely damaged forest ecosystems throughout the country, feeding on
palatable tree species, preventing regeneration, and decimating native
populations of invertebrates and birds.
 An example of biological control of an invasive species:
 The biological control of the prickly pear cactus in Australia by the caterpillar
of the moth Cactoblastis cactorum, which feeds directly on the cactus flesh.
Control of the cactus by the caterpillar has been a spectacular success and now
only scattered populations of the cactus occur.
Impacts of Humans on Ecosystem
 Fisheries management
 Stocks of commercially fished species must be managed carefully to
ensure that the catch (take) does not undermine the long term
sustainability of the fishery.
 This requires close attention to stock indicators, such as catch per
unit of fishing effort, stock recruitment rates, population age
structure, and spawning biomass.
Impacts of Humans on Ecosystems
 Fisheries Management
 Fishing is a human tradition that not only satisfies a need for food,
but is economically, socially, and culturally important.
 Decades of overfishing in all of the world’s oceans has pushed
commercially important species (such as cod) into steep decline.
 The UN’s Food and Agriculture Organization (FAO) reports that
almost seven out of ten of the ocean’s commercially targeted marine
fish stocks are either fully or heavily exploited (44%), overexploited (16%), depleted (6%), or very slowly recovering from
previous overfishing (3%).
 The maximum sustainable yield:
 the largest yield (or catch) that can be taken from a species' stock over an
indefinite period
 has been exceeded by too many fishing vessels catching too many fish, often
using wasteful and destructive methods.
Impacts of Humans on Ecosystems
 Fisheries Management
 Stock Indicators:
 For example, the stock of North Sea cod (Gadus morhua) is one of the world’s
six large populations of the economically important species.
 As one of the most intensively studied, monitored, and exploited fish stocks in
the North Sea, it is considered a highly relevant indicator of how well sustainable
fisheries policies are operating.
 Stocks of commercially fished species must be managed carefully to ensure that
the catch (take) does not undermine the long term sustainability of the fishery.
 This requires close attention to stock indicators, such as catch per unit of
fishing effort, stock recruitment rates, population age structure, and spawning
biomass.
 Currently, the North Sea cod stock is below safe biological limits and stocks are
also depleted in all waters adjacent to the North Sea, where the species is
distributed.
 Recent emergency measures plant to arrest this decline.
Impacts of Humans on Ecosystems
 Fisheries Management
 Stock indicators (continued):
 What is being done?
 A large part of the North Sea was closed for cod fishing between February
and April 2001, to protect juvenile cod.
 The TAC (total allowable catch) has been set at approximately half that set
for the year 2000. Further regulations, such as increasing net mesh size and
reducing the volume of fish discarded, are planned, and will further restrict
the effort of fishing fleets until (if) the stock recovers.
 The ICES (the International Council for the Exploration of the Sea) has
recommended a recovery plan that will ensure recovery of the spawning
stock to a level of more than 150 000t. Reduction in TAC alone are
insufficient to stop the declines.
Conservation of Biodiversity
 Conservation on a national scale generally involves setting up
reserves or protected areas to slow the loss of biodiversity.
 Nature reserves may be designated by government institutions in
some countries or by private landowners.
 The different types of nature reserves, e.g. wildlife, scenic and scientific
reserves, and National Parks, all have varying levels of protection depending
upon country and local laws.
Conservation of Biodiversity
 The Nature Conservancy is an agency concerned with
monitoring and managing the loss of biodiversity.
 The mission is to preserve the plants, animals, and natural communities
that represent the diversity of life on Earth, by protecting the lands and
waters they need to survive.
 With donations from over a million members, the Conservancy has
purchased 12,621,000 acres in the USA and a further 96,286,000 acres
outside the USA.
 Larger nature reserves usually promote conservation of biodiversity
more effectively than smaller ones.
 The ecology of the edges of ecosystems is different from the central
areas due to edge effects.
 An example of an edge effect is the egg-laying habits of the cowbird of the western U.S. It feeds in open
areas, but it lays its eggs in the nests of other birds near the edges of forests. Fragmentation of forests has
led to a considerable increase in cowbird populations because of the increase in forest edge. Wildlife
corridors allow organisms to move between different parts of a fragmented habitat, for example, tunnels
under busy roads.
Conservation
of
Biodiversity
 Active management strategies in conservation of an endangered
species:
 Mainland Island Management:
 A new strategy in conservation involves intensive management of species within a
well defined area.
 These programs have a goal of comprehensive ecosystem restoration, with species
recovery being an important consideration.
 In New Zealand, this strategy has been used very successfully to restore populations
of the endangered wattled crow, kokako.
 Kokako are at risk through forest clearance and predation by introduced
mammals, especially during the nesting season.
 Kokako recovery was implemented in a specified area of native forest which was
large enough to sustain a viable population but small enough to implement long
term pest control.
 These mainland island projects involve very intensive pest control programs and
continued monitoring of both pest populations and the species under threat. Such
programs are costly but effective; through intensive ecosystem management, the
kokako population decline had been reversed and chicks now survive to breed.
Conservation of Biodiversity
 in situ conservation of endangered species
 Habitat protection and restoration
 Most countries have a system of parks and reserves focused on whole ecosystem
conservation. These areas aim to preserve habitats with special importance and
they may be intensively managed through pest and weed control programs,
revegetation, and reintroduction of threatened species.
 ex situ conservation measures
 Captive breeding and relocation
 Individuals are captured and bred under protected conditions. If breeding
programs are successful and there is suitable habitat available, captive individuals
may be relocated to the wild where they can establish natural populations.
 Zoos, botanical gardens, and gene banks
 Many zoos specialize in captive breeding programs, while botanical gardens raise
endangered plant species.
 Universities and government agencies participate by providing practical help and
expertise. Gene banks around the world have a role in preserving the genetic
diversity of species.