Transcript Animal Ecology

Animal Ecology
Chapter 38
Ecology
 Ecology investigates the interactions among
organisms and between organisms and their
environment.
Hierarchy of Ecology
 Organism level studies focus on individuals.
 Physiological or behavioral ecology
 Population level studies examine groups of
conspecific organisms living in a particular area.
Hierarchy of Ecology
 Community level studies investigate interactions
between the populations of various species in an area.
 Species diversity - # of different species
 Interactions – predation, parasitism, competition,
symbiotic associations.
 Ecosystem level studies examine how a community
interacts with the physical environment.
Environment and Niche
 An animal’s environment includes all of the conditions
that affects survival and reproduction.
 Abiotic factors (nonliving) – soil, air, water, sunlight,
temperature, pH etc.
 Biotic factors (living) – food items, predators, parasites,
competitors, mates, hosts etc.
Environment and Niche
 Environmental factors that are directly utilized by an
animal are resources.
 Space (nonexpendable)
 Food (expendable)
Environment and Niche
 An animal’s habitat is the space where it lives.
 Size is variable
 Rotten log is a habitat for carpenter ants.
 Forest & adjacent meadow is a habitat for deer.
Environment and Niche
 The habitat must
meet the
requirements for life.
 Temp, salinity, pH
etc.
 The unique
multidimensional
relationship of a
species with its
environment is its
niche.
Environment and Niche
 Generalists can withstand a variety of environmental
conditions.
 Specialists can only tolerate a narrow range.
Environment and Niche
 The fundamental niche describes the total potential
role that an organism could fill under ideal
circumstances.
 The realized niche describes the actual role an
organism fills.
 Subset of the fundamental niche.
 Affected by competition
Population Ecology
 Population ecology is the study of populations in
relation to environment, including environmental
influences on population density and distribution, age
structure, and variations in population size.
Populations
 A population is a reproductively interactive group of
animals of a single species.
 A few individuals may migrate between populations.
 Adds gene flow
 Prevents speciation.
 Numerous small populations may be connected in this
way.
 Metapopulation
Life Tables
 A life table is an age-specific summary of the survival
pattern of a population.
 Life tables usually follow the fate of a cohort – a group of
individuals of the same age – from birth until all have
died.
Survivorship Curves
 A survivorship
curve is a graphic
way of representing
the data in a life
table.
 The survivorship
curve for Belding’s
ground squirrels
shows that the death
rate is relatively
constant.
Survivorship Curves
 Survivorship curves
can be classified into
three general types
 Type I – high survival
early in life indicates
parental care of fewer
offspring.
 Type II – constant death
rate over life span
 Type III – drops sharply
at start indicating high
death rate for young; lots
of young, no care.
Age Structure
 Populations that
contain multiple
cohorts exhibit age
structure.
 More individuals in
the younger cohorts
indicates a growing
population.
Life History Diversity
 Species that exhibit
semelparity, or “bigbang” reproduction
reproduce a single time
and die.
 Salmon
 Agave
 Favored in unpredictable
climates.
Life History Diversity
 Species that exhibit iteroparity, or repeated
reproduction, produce offspring repeatedly over time.
 Lizards often start reproducing during their second year
and will produce eggs every year of their lives.
 Favored in more predictable environments.
Population Growth
 It is useful to study population growth in an idealized
situation in order to understand the capacity of species
for increase and the conditions that may facilitate this
type of growth.
Population Growth
 If immigration and emigration are ignored, a
population’s growth rate equals birth rate minus death
rate.
Population Growth
 Zero population growth occurs when the birth rate
equals the death rate.
 The population growth equation can be expressed
as:
dN
 rN
dt
Exponential Growth
 Exponential population growth is population increase
under idealized conditions.
 Unlimited resources.
 Under these conditions, the rate of reproduction is at its
maximum, called the intrinsic rate of increase (rmax).
Exponential Growth
 The equation of exponential population growth is:
dN 
dt rmaxN
Exponential Growth
 Exponential
population growth
results in a J-shaped
curve.
Exponential Growth
 The J-shaped curve of exponential growth is
characteristic of some populations that are
rebounding.
Exponential Growth
 The global human
population has been
in exponential
growth for a long
time.
 At what point will we
surpass the carrying
capacity for our
planet?
Logistic Growth
 Exponential growth cannot be sustained for long in any
population.
 Depends on unlimited resources.
 In reality, there are one or more limiting resources that
prevent exponential growth.
Logistic Growth
 A more realistic population model limits growth by
incorporating carrying capacity.
 Carrying capacity (K) is the maximum population size
the environment can support.
The Logistic Growth Model
 In the logistic growth model, the per capita rate of
increase declines as carrying capacity is reached.
The Logistic Growth Model
 The logistic growth equation includes K, the
carrying capacity.
(K  N )
dN
 rmax N
dt
K
The Logistic Growth Model
 The logistic model
of population
growth produces
an S-shaped
curve.
The Logistic Model and Real
Populations
 The growth of
laboratory
populations of
Paramecia fits an
S-shaped curve.
The Logistic Model and Real
Populations
 Some populations
overshoot K before
settling down to a
relatively stable
density.
The Logistic Model and Real
Populations
 Some populations
fluctuate greatly
around K.
The Logistic Model and Real
Populations
 The logistic model fits few real populations, but is
useful for estimating possible growth.
The Logistic Model and Life
Histories
 Life history traits favored by natural selection may vary
with population density and environmental conditions.
K and r Selection
 K-selection, or density-dependent selection, selects
for life history traits that are sensitive to population
density.
 Few, but larger offspring, parental care.
 r-selection, or density-independent selection, selects
for life history traits that maximize reproduction.
 Many small offspring, no parental care.
Extrinsic Limits to Growth
 What environmental factors stop a population from
growing?
 Why do some populations show radical fluctuations in
size over time, while others remain stable?
Extrinsic Limits to Growth
 Abiotic limiting factors such as a storm or a fire are
density-independent – their effect does not change
with population density.
 Biotic factors such as competition or predation or
parasitism act in a density-dependent way – the effect
does change with population density.
Community Ecology
 Community ecology examines the interactions among
the various populations in a community.
Interactions
 Populations of
animals that form a
community can
interact in various
ways.
 Beneficial for one,
negative for the
other
 Predation,
Parasitism,
Herbivory
Interactions
 Beneficial for one, neutral for the other
 Commensalism
 Barnacles growing on whales
Interactions
 Beneficial for both
 Mutualism
Interactions
 Competition is a type of interaction that has a negative
effect on both.
 Community structure is often shaped by competition.
 Amensalism occurs when only one of the competitors
incurs a cost.
 Balanus & Chthamalus barnacles
Competition and Character
Displacement
 Competition occurs when two or more species share a
limiting resource.
Competition and Character
Displacement
 Competition is reduced by reducing the overlap in their
niches (the portion of resources shared).
 The principle of competitive exclusion suggests that
organisms with exactly the same niche can’t co-occur.
 One will drive the other out.
Competition and Character
Displacement
 Character
displacement occurs
when the species
partition the
resource, using
different parts of it.
 Appears as
differences in
morphology.
Competition and Character
Displacement
 Species that exploit
a resource in a
similar way form a
guild.
 Seed eaters vs.
insect eaters.
 A resource (insects)
can be partitioned
in terms of what
part of the tree is
searched.
Predator-Prey Cycles
 Many populations
undergo regular
boom-and-bust
cycles.
 These cycles are
influenced by
complex
interactions
between biotic and
abiotic factors.
Predation
 Predation refers to an interaction where one species,
the predator, kills and eats the other, the prey.
 Feeding adaptations of predators include: claws, teeth,
fangs, stingers, and poison.
 Animals also display a great variety of defensive
adaptations.
Cryptic Coloration
 Cryptic coloration, or camouflage makes prey
difficult to spot.
Aposematic Coloration
 Aposematic
coloration warns
predators to stay
away from prey.
Mimicry
 In some cases, one prey species may gain significant
protection by mimicking the appearance of another.
Batesian Mimicry
 In Batesian mimicry, a palatable or harmless
species mimics an unpalatable or harmful
model.
Müllerian Mimicry
 In Müllerian
mimicry, two or
more unpalatable
species resemble
each other.
Species with a Large Impact
 Certain species have an especially large impact on the
structure of entire communities either because they are
highly abundant or because they play a pivotal role in
community dynamics.
Keystone Species
 Keystone species are not necessarily abundant in a
community.
 They exert strong control on a community by their
ecological roles, or niches.
Keystone Species
 Field studies of sea stars exhibit their role as a
keystone species in intertidal communities.
Keystone Species
 Observation of
sea otter
populations and
their predation
shows the effect
the otters have
on ocean
communities.
Ecosystems
 An ecosystem consists of all the organisms living in a
community as well as all the abiotic factors with which
they interact.
Ecosystems
 Ecosystems can
range from a
microcosm, such as
an aquarium to a
large area such as a
lake or forest.
Ecosystems
 Regardless of an ecosystem’s size, its dynamics
involve two main processes:
 Energy flow
 Chemical cycling
 Energy flows through ecosystems, while matter cycles
within them.
Trophic Relationships
 Energy and nutrients
pass from primary
producers
(autotrophs) to
primary consumers
(herbivores) and
then to secondary
consumers
(carnivores).
Trophic Levels
 Primary production in an ecosystem is the amount of
light energy converted to chemical energy by
autotrophs during a given time period.
 Photosynthesis
Trophic Levels
 Consumers include:
 Herbivores – animals that eat plants.
 Carnivores – animals that eat other animals.
 Decomposers – feed on dead organic matter.
Trophic Levels
 Decomposition
connects all trophic
levels.
 Detritivores, mainly
bacteria and fungi,
recycle essential
chemical elements by
decomposing organic
material and returning
elements to inorganic
reservoirs.
Energy Flow
 Energy flows through an ecosystem entering as
light and exiting as heat.
Gross and Net Primary Production
 Total primary production in an ecosystem is known as
that ecosystem’s gross primary production (GPP).
 Net primary production (NPP) is equal to GPP minus
the energy used by the primary producers for
respiration.
 Only NPP is available to consumers.
Energy Transfer
 The secondary production of an ecosystem is the
amount of chemical energy in consumers’ food that is
converted to their own new biomass during a given
period of time.
Trophic Efficiency and
Ecological Pyramids
 Trophic efficiency is the percentage of production
transferred from one trophic level to the next.
 Usually ranges from 5% to 20%.
Pyramids of Production
 This loss of energy with each transfer in a food
chain can be represented by a pyramid of net
production.
 A pyramid of numbers represents the number
of individual organisms in each trophic level.
Pyramids of Biomass
 Most biomass pyramids show a sharp
decrease at successively higher trophic levels.
 Occasionally inverted
Nutrient Cycling
 Life on Earth depends on the recycling of essential
chemical elements.
 Nutrient circuits that cycle matter through an ecosystem
involve both biotic and abiotic components and are
often called biogeochemical cycles.
Toxins in the Environment
 Humans release an immense variety of toxic chemicals
including thousands of synthetics previously unknown
to nature.
 One of the reasons such toxins are so harmful, is that
they become more concentrated in successive trophic
levels of a food web.
Toxins in the Environment
 In biological
magnification,
toxins concentrate
at higher trophic
levels because at
these levels
biomass tends to
be lower.
The Three Levels of
Biodiversity
 Genetic diversity comprises:
 The genetic variation within a
population.
 The genetic variation between
populations.
 Species diversity is the variety of
species in an ecosystem or
throughout the biosphere.
 Ecosystem diversity identifies
the variety of ecosystems in the
biosphere.
Endangered Species
 An endangered species is one that is in danger of
becoming extinct throughout its range.
 Threatened species are those that are considered
likely to become endangered in the foreseeable future.
Ecosystem Services
 Ecosystem services encompass all the processes
through which natural ecosystems and the species they
contain help sustain human life on Earth.
 Purification of air and water.
 Detoxification and decomposition of wastes.
 Cycling of nutrients.
 Moderation of weather extremes.
 And many others.
Four Major Threats to
Biodiversity
 Most species loss can be traced to four major threats:




Habitat destruction
Introduced species
Overexploitation
Disruption of “interaction networks”
Extinction
 Habitat fragmentation increases local extinction and
speciation.
 Species that have larger ranges or better dispersal
abilities are better protected from extinction.
Extinction
 There have been five mass extinctions.
 Each time a large percentage of the species on
earth went extinct.