Download 5-4 How Do Communities and Ecosystems Respond to

Biodiversity, Species Interactions,
and Population Control
Chapter 5
5-1 How Do Species Interact?
 Concept 5-1 Five types of species interactions –
competition, predation, parasitism, mutualism,
and commensalism – affect the resource use and
population sizes of the species in an ecosystem.
Species
Interactions
COMPETITION
 Organisms compete for shared or limited resources
such as food, water, space, and habitats.
 Competitive exclusion principle – No two species
can occupy the exact same niche for very long
• More in Section 5-2
COMPETITION
 Interspecific competition is the competition
between member of two different species. The
result is that neither species can obtain as many
resources as they could in the absence of the
other species.
 Intraspecific competition is the competition
between member of the same species.
• This also includes the competition
for mates.
PREDATION
 Species called predators feed on other species
called prey.
 Organisms use their senses to locate objects and
their prey.
 Some predators are fast enough to catch their prey,
some hide and lie in wait, and some inject chemicals
to paralyze their prey.
PREDATION
 Some prey may escape their
predators by:
• Camouflage
• Outer protection
• Chemical warfare
• Warning coloration
• Mimicry
• Deceptive looks
• Deceptive behavior
Predator and Prey Species Can Drive
Each Other’s Evolution
 Intense natural selection pressures exist between
predator and prey populations
 Coevolution – changes in the gene pool of one
species can lead to changes in another species
• Evolution in the predator population – improved abilities to capture prey
• Evolutionary response – the prey improves its abilities to avoid capture
• The evolution of improved escape abilities should result in increased
capture abilities.
 Evolutionary “arms race”
• The levels of defense and counter-defense will continue
to escalate.
Parasitism
 Parasitism occurs when one species feeds on part
of another organism.
 Although parasites can harm their hosts, they can
promote community biodiversity.
• Some parasites live inside the host (micororganisms,
tapeworms).
• Some parasites live outside the host (fleas, ticks,
mistletoe plants, sea lampreys).
• Some have little contact with host (cowbirds – lay eggs in
another’s nest…let them take care of young.)
Parasitism
Mutualism
 In mutualism, two species interact
in a way that benefits both of them.
 Most organisms benefit through
mutualistic interactions by gaining
nutrition or protection.
Commensalism
 Commensalism is an
interaction that benefits
one species but has little,
if any, effect on the other
species.
 Epiphytes
5-2 How Can Natural Selection Reduce
Competition between Species?
 Concept 5-2 Some species develop
adaptations that allow them to reduce or avoid
competition with other species for resources.
5-2 How Can Natural Selection Reduce
Competition between Species?
 Niches (way of life)
become separated to
avoid competition for
resources.
• Reduce niche overlap
 This is also the basis of
natural selection – the
pressure that drives the
evolution of new
species.
• Chapter 4
5-2 How Can Natural Selection Reduce
Competition between Species?
 Some species evolve adaptations that allow them to
reduce or avoid competition for resources with other
species (resource partitioning).
 Each species minimizes competition with the others for food by spending
at least half its feeding time in a distinct portion of the spruce tree and by
consuming somewhat different insect species.
5-2 How Can Natural Selection Reduce
Competition between Species?
 Genetic variation and
specialized feeding niches
can lead to evolutionary
divergence.
 Use shared resources at
different:
• Times
• Places
• Ways
 Each species has a beak
specialized to take
advantage of certain types
of food resource.
5-3 What Limits the Growth of Populations?
 Concept 5-3 No population can continue to grow
indefinitely because of limitations on resources
and because of competition among species for
those resources.
Populations Have Certain Characteristics
 Populations differ in their:
•
•
•
•
Distribution
Numbers
Age structure (proportion of individuals in diff. age groups)
Density (number of individuals in a given area)
 Population dynamics – the study of changes in
population characteristics due to:
•
•
•
•
Temperature
Presence of disease organisms or harmful chemicals
Resource availability
Arrival or disappearance of competing species
Most Populations Live Together in
Clumps or Patches
 Most populations live in clumps although other
patterns occur based on resource distribution.
• Clumps can help provide protection, aid in capture of
prey, or be for mating or caring for young.
No Population Can Grow Indefinitely
 Biotic Potential
• The intrinsic rate of increase (r) is the rate a
population would grow if it had unlimited resources.
• Maximum rate of population increase under ideal
conditions.
• In nature, biotic potentials are rarely reached
 Individuals in populations with high r :
•
•
•
•
Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce
No Population Can Grow Indefinitely
In general,
 Populations with large individuals have a low biotic potential
• Humans, elephants, blue whales
 Populations with small individuals have a high biotic potential
• Bacteria, insects, microorganisms
 Examples
• Rabbits are sexually mature at 5 months of age. Their gestation period
averages 31 days and the average litter size is 6 offspring. It is possible
to have 8 litters per year. If we start with 1 fertile female and assume
that 0 die and 50 percent of the litter is female, at the end of twelve
months we have approximately 1,850 rabbits.
• Bacteria populations can double every 20 minutes
• For humans, the biotic potential (for females age 14 years to 50 years)
can average as high as 12 per female.
• Elephants have a 22 month gestation period and can usually only give
birth once every 4 years.
No Population Can Grow Indefinitely
 In nature, all rapidly growing populations will
eventually reach a size limit imposed by various
limiting factors such as:
•
•
•
•
•
•
•
Light
Water
Space
Nutrients
Competition
Predators
Infectious diseases
No Population Can Grow Indefinitely
 No population can increase its size indefinitely.
Environmental Resistance – the sum of all the factors
that act to limit the growth of a population
• Limiting factors can be food, water, light, space,
nutrients, competitors, predators, disease, etc.
• These factors act as a negative feedback on the
population size.
Carrying capacity (K): the maximum population of a
given species that a particular habitat can sustain
indefinitely without degrading the habitat.
No Population Can Grow Indefinitely:
J-Curves and S-Curves
Linear Growth
Exponential Growth
 We will be using
these terms in our
population growth
discussions
Logistic Growth
 Know them!!
No Population Can Grow Indefinitely:
J-Curves and S-Curves
 Populations grow
rapidly with ample
resources – starts off
as exponential growth
(J-Curve).
 As resources become
limited, its growth rate
slows and levels off.
No Population Can Grow Indefinitely:
J-Curves and S-Curves
 As a population levels off
(forming the S-Curve) it
often fluctuates slightly
above and below the
carrying capacity.
 This fluctuation can be small,
large, regular, or irregular.
When a Population Exceeds Its Habitat’s
Carrying Capacity…
 Populations which overshoot
their carrying capacity suffer a
crash (or dieback)
 This situation is made possible
by a reproductive time lag
• The time needed for birth/death
rates to change in response to
environmental changes.
 Overshooting the carrying
capacity can adversely affect
the ecosystem as well
• Decrease the carrying capacity
Under Some Circumstances Population
Density Affects Population Size
 Population density: the number of individuals in a
population found in a particular area.
• Some population controls are density-dependent.
This means that they have a greater effect as the
population density increases.
• e.g. biotic factors, predation, competition, disease,
scarcity of food
• Other population controls are density-independent
and are not affected by population density.
• e.g. abiotic factors like weather, pollution, fire
Species Have Different Reproductive Patterns
 r-selected species – Large
number of smaller offspring
with little parental care.
 They overcome the massive
loss of offspring by having so
many that even if only very
few survive – it is enough.
 Opportunists – reproduce
and disperse at a rapid rate
(r) when conditions are
favorable.
Species Have Different Reproductive Patterns
 K-selected species – Fewer,
larger offspring with higher
invested parental care.
 Produce offspring later in life
and put a lot of energy into
one offspring.
 Competitors – can compete
well for resources when the
population is close to the
carrying capacity (K).
Species Have Different Reproductive Patterns
Species Have Different Reproductive Patterns
Answer:
R-selected species – they are more adaptive to
changing environmental conditions.
Since they have many offspring and much faster,
they can also evolve much more quickly.
Population Change Curves in Nature
 Population sizes often vary in regular cycles when the
predator and prey populations are controlled by the
scarcity of resources.
 These populations are regulated through:
• Top-down population regulation – predation, parasitism
• Bottom-up population regulation – the scarcity of resources
-- NOT IN TEXTBOOK -Survivorship Curves:
 The way to represent the age structure of a
population is with a survivorship curve.
• Late loss population (Type I)
• Live to an old age
• Humans, elephants
• Constant loss population (Type II)
• Die randomly at all ages
• Most birds
• early loss population (Type III)
• Most members die at young ages
• Fish, amphibians, many insects
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Concept 5-4 The structure and species
composition of communities and ecosystems
change in response to changing environmental
conditions through a process called ecological
succession.
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 New environmental conditions allow one group of
species in a community to replace other groups.
 Ecological succession: the gradual change in
species composition of a given area
• Primary succession: the gradual establishment of
biotic communities in lifeless areas where there is no
soil or sediment.
• Secondary succession: series of communities
develop in places containing soil or sediment.
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Primary succession begins with an essentially
lifeless area where there is no soil.
 The weathering of rocks
and the introduction of
hearty plants begins to
form soil.
 Eventually, more and
more plant species are
able to take hold.
 This process takes a
very long time.
• (100’s -1000’s of years)
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Primary succession begins with an essentially
lifeless area where there is no soil.
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Early successional plant species, pioneer
• Lichens, mosses
• Trap windblown sediments, moisture
• Break apart rocks
 Midsuccessional plant species
• Grasses, low shrubs
 Late successional plant species
• Mostly trees
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Secondary succession occurs when the
natural community has been disturbed,
removed, or destroyed.
 This disturbance
could be as a result
of a fire, flood, or
humans.
 The key is that soil
already exists so
that this process
many only take a
100-200 years.
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental Conditions?
 Secondary succession occurs when the
natural community has been disturbed,
removed, or destroyed.
Succession Doesn’t Follow a
Predictable Path
 The course of succession cannot be precisely predicted.
 Traditional view
• Balance of nature and a stable climax community will
always be achieved.
 Current view
• Ever-changing mosaic of patches of vegetation
• Succession involves species competing for enough light,
nutrients and space which will influence it’s trajectory and
end result.
• State of continual disturbance and change