Download Principles of Ecology (APES)

Principles of Ecology (APES)
Abiotic and Biotic Factors in an Ecosystem
Major Living Components
of Ecosystems
Flow of Energy
Energy Flow
A. Producers/autotrophs
1. Photosynthetic organisms
2. Chemosynthesis
a. Specialized organisms called chemoautrophs covert simple compounds from
their env. into more complex nutrient compounds without sunlight
i. Able to synthesize all of the organic compounds they need from inorganic
raw materials
b. Chemosynthesis is derived from special methods of respiration involving the
oxidation of various inorganic materials such as hydrogen sulfide, ammonia, and
iron-bearing compounds.
B. Consumers/Heterotrophs
1. Herbivores
2. Carnivores
3. Omnivores
4. Scavenger
5. Detrivores
a. Feed on detritus, or parts of dead organisms, cast-off fragments, and wastes of
living things
b. Detritus feeders (crabs, carpenter ants, termites, earthworms)
i. Extract nutrients from partly decomposed organic matter in leaf litter, plant
debris, and animal wastes
6. Decomposers (certain bacteria and fungi)
a. Break down dead organic matter to get nutrients
b. Release simpler inorganic compounds into the soil and water, where they can be
taken up as nutrients by producers
A. Natural energy inputs into the ecosystem include
1. Solar radiation
2. Input of seeds (in the ecosystem)
3. Animal immigration
4. Erosional processes.
B. Natural energy outputs from an ecosystem include
1. Reflection of infrared into space,
2. Conduction of infrared energy into the env (heat)
3. Seed dispersal out of the ecosystem
4. emmigration of animals from the ecosystem
5. Leaching of soil nutrients into the ground
C. Sun’s energy is the driving force for the energy pyramid for all biological processes
1. Less than 3% of all sunlight that reaches the Earth is used (or fixed) for
photosynthesis (Review the process of photosyntheis and cellular respiration)
D. Food Consumption and Energy
1. Energy that is obtained by heterotrophs eventually is returned to the system (Law of
Conservation of Energy) through....
a. Energy used for cellular respiration and waste heat
b. Energy expanded for obtaining food, reproduction, and other activities
c. Energy released through the decay of waste products and decay of the organism
d. Transfer of the energy to an organism higher in the food chain through
consumption
E. Food chains/webs
Autotroph
Primary Producer
Transfer of Energy
1.
2.
Herbivore
Primary Consumer
Primary Carnivore
Secondary Consumer
Secondary Carnivore
Tertiary Consumer
Amount of net energy that is transferred from one trophic level to the next includes,
but is not limited to the following:
a. Inefficiences (heat loss)
b. Energy expended to obtain food
c. Cellular respiration required to maintain the organism
d. Reproductive activities
Detritus food chains are significantly different:
etc.
a.
b.
c.
d.
F.
(owl pellet lab)
(primary productivity lab)
Size of organisms are much smaller
Organisms exist in env. rich in nutrients so energy is not needed to obtain food
Organisms are generally not motile
Trophic levels are more complex and interrelated
i. These kinds of food chains often have many different species of algae,
bacteria, fungi, protozoa, slime molds, insects, arthropods, crustaceans, and
worms
3. Rate of decomposition and numbers of decomposers is generally in equilibrium with
the amount of material available
4. The concept of linear food chains allows understanding of energy-relationships and
trophic-level hierarchies
a. However, the interrelationships among living organisms and codependences of
all organisms within an ecosystem functioning together in balance creates the
much more complex food web
Each trophic level in a food chain/web contains a certain amount of biomass and therefore
energy
1. Biomass is the dry weight of all organic matter contained in its organisms
a. Chemical energy stored in biomass is transferred from on trophic level to another
i. With each transfer, some usable energy is degraded and lost to the env. as
low-quality heat
ii. Only a small portion of what is eaten and digested is actually converted into
an organisms bodily material or biomass (review biomass pyramid)
iii. The amount of usable energy available to each successive trophic level
declines (review the energy pyramid)
 The percentage of usable energy transferred as biomass from one
trophic level to the next is called ecological efficiency
 It ranges from 5-20% (a loss of 80-95%) depending on the type of
species and the ecosystem involved
 Typically about a 10% reduction at each trophic level
 The more trophic levels, the greater the cumulative loss of usable energy
2. Gross Primary Productivity (GPP) – the rate at which an ecosystem’s producers
convert solar energy into chemical energy as biomass
a. AKA: the rate at which plants or other producers use photosynthesis to make
more plant material (biomass)
b. Greatest GPP is generally located...
i. In the shallow waters near continents
ii. Along coral reefs where abundant light, heat, and nutrients stimulate the
growth of algae
iii. Where upwelling currents bring nitrogen and phosphorous from the ocean
bottom to the surface
c. Lowest GPP is generally located...
i. Deserts and other arid regions because of their low precipitation and high
temps
ii. The open ocean due to the lack of nutrients and sunlight except near the
surface
3. Net Primary Productivity (NPP) – available for use as food by other organisms
(consumers) in an ecosystem
a. The rate at which energy for use by consumers is stored in new biomass
NPP =
b.
c.
Rate at which producers store
chemical energy as biomass
(produced by photosynthesis)
-
Rate at which producers use
chemical energy stored as biomass
(through aerobic respiration)
Most productive ecosystems and life-zones for NPP
i. Estuaries
ii. Swamps and marshes
iii. Tropical rain forests
Least productive...
i. Open oceans
 Even though this is one of the least productive areas, due to its shear
size covering the earth, it produces more of the earth’s NPP than any
other ecosystem and life-zones
ii. Tundra (both arctic and alpine)
iii. Desert
d.
e.
f.
Measured in units of the energy or biomass available to consumers in a specified
area over a given time
The NPP without human activity or influences has been estimated to be 150
million tones of biomass per year.
i. Humans have caused a 12% decline through deforestation
ii. Humans utilize ~ 27% of the NPP for their own purposes (food, building
material, energy, etc.) or by converting productive land to other uses
iii. Together this represents ~ 40% of the NPP on Earth committed to the use of
humans.
 All other life forms on Earth are left to share the remaining 60%
Since humans use 40% of the carrying capacity of earth (as measured through the
NPP), and assuming all primary plant growth was utilized for human purposes
and no other effects (ie pollution, plague, etc.), due to increased density were
taken into account, the theoretical maximum sustainable human population at
100% of the carrying capacity would be calculated as:
100%
40%
x
6 billion people =
15 billion people
(current population)
i.
Biological Diversity and
Evolution
The Threat to Biodiversity
Biological Evolution
Some scientists believe that we could reach a population of 15 billion people
(in the 21st century) and hence the carrying capacity
 This would mean that every square meter of the earth would be
dedicated to humans (do you believe this will happen? Why or why
not?)
A. The different life-forms and life-sustaining processes that can best survive the variety of
conditions currently found on the earth.
1. Genetic diversity
a. Variety in the genetic makeup among individuals within a species
2. Species diversity
a. Variety among the species or distinct types of living organisms found in different
habitats
i. Species richness – total number of species
ii. Species evenness – the relative abundance of species
iii. Species dominance – the most abundant species
3. Ecological diversity
a. Variety of forests, deserts, grasslands, streams, lakes, oceans, coral reefs,
wetlands, and other biological communities
4. Functional diversity
a. Biological and chemical processes or functions such as energy flow and matter
cycling needed for the survival of species and biological communities
5. Diversity Increasers/Decreasers
Diversity Increasers
Diversity Decreasers
Diverse Habitats
Environmental Stress
Disturbance in the habitat – fires, storms,
etc.
Environmental conditions (temps, rainfall,
food supply, etc.) with low variation
Extreme environments
Trophic levels with high diversity
Extreme amounts of disturbance
Middle stages of succession
Introduction of species from other areas
Evolution
Geographic Isolation/allopatric speciation
Extreme limitations in the supply of a
fundamental resource
B. Biological Evolution (REVIEW THE THEORY OF EVOLUTION)
1. Refers to the change in inherited characteristics of a population from generation to
generation.
a. Can result in speciation
2. One of the features that distinguishes life from everything else in the universe
3. One way process...
a. Once a species is extinct, it is gone forever.
b. Once a new species evolves, it cannot evolve backwards into its ancestry
4. Four processes that lead to evolution
a. Mutation
i. When a cell divides, the DNA is replicated so that each new cell gets an
identical copy
Sometimes there is an error or a failure in the replication process
 results in a change in the DNA sequence and therefore a change in
inherited characteristics
iii. Sometimes an external env’tal agent (chemicals, radiation, etc.) comes in
contact with the DNA and alters it
iv. Not all cells or offspring with mutations can survive, but in other cases, the
mutation adds variety to the inherited characteristics
 In some cases, individuals that survive with mutations are so different
from their parents that they cannot reproduce with the normal offspring
 This causes speciation
 Mutations can result in a new species whether or not that species is
better adapted than its parental species to the env.
Natural Selection
i. When there is variation within a species, some individuals may be better
suited to the env. than the others
ii. Organisms whose biological characteristics better fit them to the env. have
relatively more offspring than those whose characteristics are less fit
 Results in these organisms are better represented by descendants in
future generations
iii. Four primary characteristics...
 Inheritance of traits from one generation to the next and some variation
in these traits (genetic variability)
 Environmental variability
 Differential reproduction that varies with the env.
 Influence of the env. on survival and reproduction
iv. Natural selection operates in 3 ways; stabilizing, directional, or disruptive
(check out http://www.evotutor.org/Selection/Sl5A.html to see how each
works)
 Stabilizing – individuals that deviate too far from the average conditions
are removed resulting in a decrease in diversity, maintenance of a stable
gene pool, and no evolution
 Directional – Individuals towards one end of the distribution may do
well, resulting in a frequency distribution toward this advantage in
subsequent generations, affecting the gene pool and therefore promotes
evolution
 Disruptive – acts against individuals that have the average condition and
favors individuals at the extreme ends, affecting the gene pool and
therefore promotes evolution
iv. When natural selection takes place over a very long period of time, a number
of characteristics can change (resulting in speciation)
v. The accumulation of these changes may be so great that the present
generation cannot reproduce with individuals with the original DNA
structure; can be caused by...
 Behavioral isolation - produced by behavioral differences
 Geographic isolation/allopatric speciation - produced by physical
separation
 Temporal isolation - produced by different mating times
vi. A consequence of natural selection is that when two species compete, the
more fit species will win and persist and the less fit species will lose and
will either migrate, become extinct, or partition the resource and utilize a
sub-set of the same resource.
 This is known as the competitive exclusion principle
 Two species that have exactly the same requirements cannot coexist in
exactly the same habitat
 Example: British red and American grey squirrels – American grey’s
were intentionally introduced to G.B. because they thought it would be a
nice addition to their landscape. The grey was an introduced/exotic
species. The grey’s and red’s compete for the same resources with the
introduced species winning the competition. Red’s are expected to
become extinct on the mainland within 20 years. Introduced Species
Migration
ii.
(bean lab)
b.
c.
i.
Biotic Relationships
Types of Interactions
A.
B.
C.
D.
Migration of one population into a habitat previously occupied by another
population can lead to changes in gene frequency
 Even species that cannot physically move themselves (like plants) can
have migrating seeds that end up in new habitats
ii. Important process over geologic time
 Animals that crossed the land bridge between Siberia and Alaska were
eventually cut off by rising sea water
d. Genetic Drift
i. Refers to changes in the frequency of a gene in a population as a result of
chance rather than mutation
 Chance may determine which individuals become isolated from the
main population and thus which characteristics are most common for
that smaller group
 The individuals may not be better adapted to the env.
ii. Generally considered to be an especially serious problem with populations
become very small (ie endangered species)
 Characteristics that are less adapted to existing env’tal conditions may
dominate, making the chance of survival of the species less likely
 Genetic variability of the species is greatly reduced, meaning that its
ability to adapt to future changes in the env. through natural selection
has been reduced
iii. Can occur in any small population and may also present problems when a
small group is isolated from the main population by chance
Commensalism (+ 0)
1. One species benefits from the relationship but the other is neither harmed nor
benefited (symbiotic)
a. Example: Certain mites carry out most of their life activities within the flower of
a particular plant species. Hummingbirds that pollinate these flowers transport
the mites from old to new flowers.
Amensalism (- 0)
1. The interaction between two species whereby one species suffers and the other
species is not affected
a. Alleopathy – occurs when one species releases a chemical substance to inhibit
the growth of another species
i. Example: black walnuts exude a chemical called juglone, a compound that
affects plant growth. Juglone can be toxic to many plants but not necessarily
all plants. It has been shown that apple trees do not respond well at all to
growing near black walnuts.
b. Example: Cormorants and herons nest in trees. The toxic excrement of the birds
can eventually kill the trees and the associated understory vegetation. They
receive no benefit (or harm) from the damage caused to the understory plants.
Competition (- -)
1. Interspecific – organisms from different species compete for the same resource
a. Example: In certain areas of the Southwest, the population of Gila woodpeckers
is decreasing, and the population of starlings is increasing Both birds nest in the
cavities of giant cacti
2. Intraspecific – organisms from the same species compete for the same resource
a. Example: Africanized honeybees (killer bees) and European honeybees (our
typical honeybees) are subspecies of one another and use the same resources for
food.
b. Territoriality - Organisms defend specific area containing resources, primarily
against members of own species.
3. Exploitation – competition that occurs when indirect effects reduce resource(s).
a. Example: One species obtains the resources first such as when there’s a big
fruiting gree with orangutans, macaques, and colobines all eating at once.
There’s no interaction or aggression between them, but they’re still reducing the
amount of food available to the others.
4. Interference – competition that occurs when an organism prevents physical
establishment of another organism in the habitat.
a. Example: Hummingbirds exclude other hummingbirds (as well as bees and
moths) from flowering plants
Mutualism (+ +)
1.
E.
F.
G.
H.
I.
Population Size and
Carrying Capacity
A.
The interaction between two species whereby both species mutually benefit
(symbiotic)
a. Example: Mycorrihazae fungus helps the plant to absorb soil nutrients – roots of
plants supply carbohydrates to mycorrhizae
2. Symbiotic Mutualism – physical interaction but either species cannot live without the
other
a. Example: Lichens are made up of an algae and a fungus
3. Nonsymbiotic Mutualism – no physical interaction but either species cannot live
without the other
a. Example: insect pollinators and flowers
Neutralism (0 0)
1. An interspecific interaction whereby neither population really affects the other
a. Example: Grizzly bear and butterfly
Parasitism (+ -)
1. Species that obtain food at the expense of their host (symbiotic)
a. Example: Certain young clams attach themselves to the gills of a fish. In a short
time, each clam becomes surrounded by a capsule formed by cells of the fish.
The clam feeds and grows by absorbing nutrients from the fish’s body
Predation (+ -)
1. Species that obtain food at the expense of their prey.
a. Example: lions preying upon zebras
2. Many feedback mechanisms have evolved to keep numbers stable.
Saprophytes (+ 0)
1. Species, especially fungus or bacteria, that grow on and derive their nourishment from
dead or decaying organic matter.
a. Include microbes, some insects, grubs, snails, slugs, beetles, and ants
i. They aid in recycling valuable nutrients from dead organic matter that is then
released back into the soil to be reabsorbed rapidly by plants and trees.
ii. Decayed matter contains essential nutrients like iron, calcium, potassium,
and phosphorous
 necessary to promote healthy plant growth
Keystone Species
1. A species or group of species whose activity has an inordinate influence on the
structure of its community
a. Example: Gopher tortoise in GA
If a population in a community is left unchecked, the maximum population growth rate
rmax, can increase exponentially
1. Exponential growth occurs initially when...
a. Populations are introduced into new or unfilled niches
b. The populations numbers have been seriously reduced due to a catastrophic
events and the population is rebounding
2. Most populations never attain this type of increase
a. Maximum population growth rates are determined by many factors including
i. Age of reproduction
ii. Clutch size
iii. Viability of offspring
iv. Interspecific/Intraspecific competition
v. Predation
vi. Limitations to resources
3. Logistic Growth (S-curve) is used to describe the pattern of growth over a period of
time of a population when organisms of that species move into an empty niche
a. Logistic growth rates are density-dependent and are characterized by 2
parameters and 2 variables
i. Parameter 1: Maximum population growth rate (rmax)
ii. Parameter 2: Carrying capacity (K)
iii. Variable 1: Population size (N)
iv. Variable 2: Time
b. Process
i. Unlimited resources allow for rapid reproductive phase
ii. The carrying capacity (K) is reached as resources become limited
 Each organism has less share of resources
iii. The larger the population (N) becomes, the slower the growth rate
iv. Population size may stabilize or fluctuate (oscillation) around the carrying
capacity
v. Individuals either experience higher death rates and/or lower fecundity
(ability to reproduce)
vi. When birth rate = death rate, then equilibrium has been achieved
B. Calculating Population Growth
1. Simple Growth Rate of a Population
N1 = N0 + B – D + I – E x 100
1000
B = Birth rate
D = Death rate
I = Immigration
E = Emmigration
N0 = Population size at an initial time
N1 = Population size at a later time
2.
Intrinsic Rate (r) of Increase for Population Growth
r=B-D
r = Intrinsic rate of increase
B = Birth rate
D = Death rate
3.
Rate of Change of Population Size
dN
dt
=
rN
r = Intrinsic rate of increase
dN = N1 – N0
dt = Time
rN = Rate of change of population size
4.
Net Growth Rate of a Population
R0
=
N1
N0
R0 = Net growth rate of a population
N0 = Population size at an initial time
N1 = Population size at a later time
5.
Doubling Time for a Population
Dt
=
70
R0
Dt = Doubling time for a population
R0 = Net growth rate of a population
6.
Annual % Rate of Natural Population Change
%
=
(B – D)
x 100
1000
% = Annual percentage rate of natural population change
B = Birth rate
D = Death Rate
C. Major characteristics of a population; populations change in response to env’tal stress or
changes in env’tal conditions
1. Size
2. Density
a. Density-independent population controls affect a population’s size regardless of
its population density (floods, fires, hurricanes, unseasonable weather, habitat
destruction, pesticide spraying, etc.)
b. Density-dependent population controls limiting factors that have a greater effect
as a population’s density increases (competition for resources, predation,
parasitism, disease, etc.)
3. Dispersion
a. Random – individuals are located haphazardly in space in no particular pattern
b. Uniform – individuals are evenly spaced out
c. Clumped – pattern most common in nature where individuals arrange themselves
according to the availability of resources
4. Age distribution
D. Minimum Viable Population (MVP)
1. Describes the smallest possible size that a population can exist at, without facing
extinction from demographic, environmental, genetic events and natural catastrophes.
a. The exact probability is usually between 90% and 95%
b. The time survival is usually 100 to 1000 years
2. The MVP can be calculated using computer simulations known as PVA (Population
Viability Analysis), where populations are modeled and future population dynamics
are projected.
a. For example (and this is just an example, these figures are not real), a PVA
(essentially a computer simulation of the population) might be run repeatedly on
a Giant Panda population. It might be found that with a starting population of 50
Pandas, after 100 years of running the model, the simulated population goes
completely extinct 30 out of 100 runs. It might go extinct because you start to get
inbreeding depression, or a natural catastrophe wipes out a large number of the
Pandas, there are various reasons. Extinction 30 out of 100 runs, means that the
population survived on 70 of the runs, giving a survival probability of 70%. Now
lets say you re-run the simulation but this time with a starting population of 60
Pandas. This time the Panda population only goes extinct on 4 of the 100 runs.
The Panda population is now large enough to recover from or buffer the effects
of natural catastrophes and other stochastic events, so the population is able to
survive more easily. With a starting population of 60, the survival probability is
96 out of 100, or 96%. So 60 Pandas becomes your Minimum Viable Population.
You could then re-run the simulation with a range of starting sizes to determine
this figure more accurately (i.e perhaps it is 57 or 58).
(population sampling lab)
If this was a real situation, and you were a conservation manager, you would
know that you must somehow increase the number of Pandas in your reserve to at
least 60 if you want them to survive for the next 100 years. This might be
achieved by a captive breeding program, or through bringing them in from other
reserves.
E. Populations vary in their capacity for growth (biotic potential)
1. The intrinsic rate of increase (r) is the rate at which a population would grow if it had
unlimited resources
2. Generally, individuals in populations with high intrinsic rate of increase
a. Reproduce early in life
b. Have short generation times (the time between successive generations)
c. Can reproduce many times
d. Have many offspring each time they reproduce
F. Environmental resistance consists of all the factors acting jointly to limit the growth of a
population
1. The population size of a species in a given place and time is determined by the
interplay between its biotic potential and environmental resistance
2. Together biotic potential and environmental resistance determine the carrying
capacity (K)
3. The intrinsic rate of increase (r) of many species depends on having a certain
minimum population size called the minimum viable population (MVP)
a. If a population drops below the MVP needed to support a breeding population...
i. certain individuals may not be able to locate mates
ii. genetically related individuals may interbreed and produce weak or
malformed offspring
iii. The genetic diversity may be too low to enable adaptation to new env’tal
conditions
b. The intrinsic rate of increase falls and extinction is likely
G. The carrying capacity (K) is not a simple, fixed quantity and is affected by many factors
(See carrying capacity section above)
1. Competition within and between species
2. Immigration and emigration
3. Natural and human-caused catastrophic events
4. Seasonal fluctuations in the supply of food, water, hiding places, and nesting sites
H. Population change curves in nature
1. Stable – fluctuates slightly above and below its carrying capacity
2. Irregular – fluctuates irregularly with no known reason
3. Cyclic – sharp increases followed by sharp crashes over a fairly regular time period
4. Irruptive – population explosions with high peaks and then crash to a more stable
lower level
I. The Role of Predation in Controlling Population Size
1. Some species that interact as predator/prey undergo cyclic changes in their numbers,
with sharp increases followed by periodic crashes
a. For decades, predation has been the explaination for the ~10 year population
cycles of the Canadian lynx and snowshoe hare
i. The top-down control hypothesis for the lynx and hare...
 Lynx preying upon hares periodically reduces the hare population
 The shortage of hares periodically reduces the lynx population, which
allows the hare population to recover
 At some point, the lynx population increases to take advantage of the
increase in the hare population
b. Some research has cast doubt on this top-down control hypothesis
i. Snowshoe hares tend to show the same 10 year cycle in areas where no lynx
are found
 Researchers hypothesize that the periodic crashes of hares when lynx
are not present could be associated with food supply
 Large populations of hares die when they consume food plants faster
than they can be replenished (esp. winter)
 Have a decrease in the quality/quantity of their food
 When hare population decreases, plant matter has a chance to recover
 Eventually hare population increases to take advantage of the increase in
the food supply.
 This is called the bottom-up control hypothesis
 Instead of the lynx controlling the hare population, it is the hare
population controlling the lynx population
c. These 2 hypotheses are not mutually exclusive
i. 10 year population cycles of hares in boreal forests is caused by the
interaction between predation (ALL predators, not just lynx) and food supply
(esp. winter) with predation being the dominant process
d. According to biologists, genuine cases of top-down control systems does exist in
a variety of ecosystems
J. Reproductive Patterns and Survival
1. Asexual reproduction
a. All offspring are exact genetic copies (clones) of a single parent
2. Sexual reproduction
a. Offspring are a combination of the genetic material from the combining of
gametes/sex cells from both parents
i. 97% of known organisms uses sexual reproduction to perpetuate their
species
b. Sexual reproduction has several ecological costs and risks including...
i. Females have to produce 2x as many offspring to maintain the same # of
young in the next generation as an asexually reproducing organisms since
males do not give birth
ii. Chances of genetic errors and defects increase during the splitting and
recombination of chromosomes
iii. Mating entails costs such as...
 time-consuming courtship and mating rituals
 disease transmission
 injury inflicted by males during mating
Despite the ecological costs and risks, sexual reproduction...
i. Provides a greater genetic diversity in the offspring thereby improving the
chance of reproducing when env’tal conditions change (adaptations/natural
selection)
ii. Males can gather food for the females and young
iii. May protect mother/offspring and train the young for survival
Types of reproductive patterns
a. r-selected/r-strategists/opportunistic species
i. Species with a capacity for a high intrinsic rate of increase (r).
ii. Reproduce early and put most of their energy into reproduction
 Example: algae, bacteria, rodents, annual plants, most insects
iii. Characteristics
 Have many (usually small) offspring each time they reproduce
 Reach reproductive age quickly
 Short generation times
 Give offspring little or no parental care or protection
 Short lived (usually <1 year)
iv. Species with this reproductive pattern overcome the massive loss of their
offspring by producing so many unprotected young that a few will survive to
reproduce
v. Tend to reproduce and disperse rapidly when conditions are favorable or
when a disturbance opens up a new habitat or niche for invasion (hence
opportunistic)
vi. Changed env’tal conditions from disturbances can allow opportunistic
species to gain a foothold but their population may crash due to...
 Changing or unfavorable env’tal conditions
 Invasion by more competitive species
vii. Tend to go through irregular and unstable boom-and-bust cycles
b. k-selected/k-strategists/competitor species
i. Put fairly little energy into reproduction
ii. Tend to reproduce later in life
iii. Have fewer offspring with long generation times
 May be fewer but tend to be stronger and can compete for resources
iv. Put most of their energy into nurturing and protecting young until they reach
reproductive age
v. Typical offspring...
 Develop inside their mothers
 Fairly large
 Mature slowly
 Cared for and protected by one or both parents
vi. Tend to do well in competitive conditions when their population size is
nearing the carrying capacity (K) of their env.
vii. Populations tend to follow a logistic growth curve (S-curve)
 Examples: most large mammals (elephants, whales, humans), birds of
prey(hawks, owls, eagles), large and long lived plants (saguaro cactus,
oak trees, redwood trees)
viii. Thrive best in ecosystems with fairly constant env’tal conditions
c. Something in between r-select and k-select organisms?
i. Many have reproductive patterns between the extremes or they can change
from one extreme to the other under certain env’tal conditions
ii. In ag, we raise both r-select (crops) and k-select (livestock) organisms for
our survival
d. Survivorship curves
i. The availability of suitable habitat for individuals of a population in a
particular area is what determines its ultimate population size.
 Regardless of how fast a species reproduces, there is a limit to growth
based on resources!
ii. Individuals of species with different reproductive patterns tend to have
different life expectancies
 Survivorship curves illustrate these life spans
iii. Three types of survivorship curves
c.
r-Select and k-Select Species
Remember: Biotic potential is
the maximum rate of growth a
population can experience
without any environmental
resistance (factors that work
to decrease a population; ie
limiting factors)
3.

Late loss curve – typical for k-select species due to the care and
protection provided by the parents until reproductive age
 Early loss curve – typical for r-select species due to high juvenile
mortality but high survivorship once the young reach a certain age
 Constant loss curve – characteristic of species with intermediate
reproductive patterns with a fairly constant rate of mortality in all
cohorts (songbirds, lizards, prey animals with constant threat of being
eaten)
K. Conservation Biology: Sustaining Wildlife Populations
1. Established back in the 1970’s
2. Based on Aldo Leopold’s ethical principle that something is right when it tends to
maintain the earth’s life-support systems for us and other species and wrong with it
does not.
3. Uses the best available science to take action to preserve species and ecosystems and
try to address the following questions...
a. Which species are in danger of extinction?
b. What is the status of the functioning of ecosystems, and what ecosystem services
of value to humans and other species are we in danger of losing?
c. What measures can we take to help sustain ecosystem functions and viable
populations of wild species?
4. To understand the status of natural populations, we must...
a. Measure the current population size
b. Project how population size is likely to change with time
c. Determine whether existing populations are likely to be sustainable
5. Three underlying principles (holistic worldview):
a. Biodiversity is necessary to all life on earth and should not be reduced by human
actions
b. Humans should not cause or hasten the extinction of wildlife populations and
species or disrupt vital ecological processes
c. The best way to preserve earth’s biodiversity and ecological functions is to
protect intact ecosystems that provide sufficient habitat for sustaining natural
populations of species
L. Human Impacts on Ecosystems
1. Humans have used technology to alter much of the rest of nature in the following
ways:
a. Fragmenting and degrading habitat
b. Simplifying natural ecosystems (plowing, clearing forests, introduction of
monocultures, etc.)
c. Using, wasting, or destroying an increasing percentage of the earth’s net primary
productivity that supports all consumers species (including humans)
d. Strengthening some populations of pest species and disease-causing bacteria by
speeding up natural selection and causing genetic resistance through overuse of
pesticides and antibiotics
e. Eliminating some predators (killing off wolves on your farm, etc.)
f. Deliberately or accidently introducing new or non-native species (Kudzu or grey
squirrels to G.B.)
g. Overharvesting renewable resources (like trees and grassland overgrazing)
h. Interferring with the normal chemical cycling and energy flows in ecosystems
2. How to balance our existence with nature (finding sustainability)
a. Maintain a balance between simplified, human-altered ecosystems and the
neighboring, more complex natural ecosystems on which we and other life-forms
depend
b. Slow down the rates at which we are altering nature for our purposes
Comparing the Risks and Benefits to Population Managment
Ecological Succession
A. The gradual change in species composition of a given area
1. During succession, some species colonize an area and their populations become more
numerous, whereas populations of other species decline and even disappear
2. Ecologists recognize two types of ecological succession depending on the conditions
present at the beginning of the process
a. Primary Succession – the gradual establishment of biotic communities on nearly
lifeless ground
i.
Nearly lifeless ground can be categorized as...
 Bare rock exposed by a retreating glacier or severe soil erosion
 Newly cooled lava
 An abandoned highway or parking lot
 Newly created shallow pond or reservior
ii. Process
 Pioneer species – lichens and mosses Succession and Soil Formation
 Early successional plant species – low growing plants
 Midsuccessional plant species – Herbs, grasses, and low shrubs
 Late successional plant species – mostly trees
b. Secondary Succession – involves the reestablishment of biotic communities in an
area where some type of biotic community is already present
i. Reestablishment areas can be categorized as...
 Abandoned farmlands
 Burned/cut forests
 Heavily polluted streams
 Damaged land from floods, dams, volcanic eruptions, etc.
ii. Process
 Annual weeds
 Perennial weeds and grasses
 Shrubs
 Young pine forest
 Mature oak-hickory forest
iii. Species
 Early successional species – rabbit, quail, dove, pocket gopher
 Midsuccessional species – elk, moose, deer, bluebirds, snowshoe hare
 Late successional species – turkey, martin, grey squirrel
 Wilderness species – grizzly bear, wolf, great horned owl, caribou
C. Species replacement in ecological succession
1. Facilitation
a. One species modifying an env. to the extent it meets the needs of another species
i. Lichens and mosses gradually build up soil on rock in primary succession so
that other species of herbs and grasses can become established
2. Inhibition
a. One species modifies the env. to an extent it is not suitable for another species
b. Often occurs with interference competition
c. Succession can only proceed when some type of disturbance removes most of the
inhibiting species (fire, bulldozer, etc.)
3. Tolerance
a. When species are not affected by the presence of other species
b. May explain why late successional plants can thrive in mature communities
without eliminating some early successional and midsuccessional plants
D. Other terms associated with succession
1. Allogenic
a. Caused by changes in environmental conditions that create conditions conducive
to new plant communities
2. Autogenic
a. Succession caused by changes both in the plant community and the env.
3. Progressive
a. Occurs over time whereby the communities become more complex by having a
higher species diversity and greater biomass
4. Retrogressive
a. Occurs over time when env’tal variables deteriorate and thereby changing the
status quo and causing communities to become less diverse and contain less
biomass
b. May be allogenic such as the introduction of grazing animals into grasslands
resulting in the destruction of the grasses.