Animal EcologyChapter 38

EcologyEcology investigates the interactions among

organisms and between organisms and their environment.

Hierarchy of EcologyOrganism level studies focus on individuals.

Physiological or behavioral ecology

Population level studies examine groups of conspecific organisms living in a particular area.

Hierarchy of EcologyCommunity 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 NicheAn 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 NicheEnvironmental factors that are directly utilized

by an animal are resources.Space (nonexpendable)Food (expendable)

Environment and NicheAn animal’s habitat is the space where it lives.

Size is variableRotten 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 NicheGeneralists can withstand a variety of

environmental conditions.

Specialists can only tolerate a narrow range.

Environment and NicheThe 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 EcologyPopulation 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.

PopulationsA population is a reproductively interactive

group of animals of a single species.A few individuals may migrate between

populations.Adds gene flowPrevents speciation.

Numerous small populations may be connected in this way.Metapopulation

Life TablesA 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 CurvesA 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 CurvesSurvivorship curves

can be classified into three general typesType 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 StructurePopulations that

contain multiple cohorts exhibit age structure.More individuals

in the younger cohorts indicates a growing population.

Life History DiversitySpecies that exhibit

semelparity, or “big-bang” reproduction reproduce a single time and die.SalmonAgaveFavored in

unpredictable climates.

Life History DiversitySpecies 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 GrowthIt 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 GrowthIf immigration and emigration are ignored, a

population’s growth rate equals birth rate minus death rate.

Population GrowthZero population growth occurs when the birth

rate equals the death rate.

The population growth equation can be expressed as:

dN

dtrN

Exponential GrowthExponential 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 GrowthThe equation of exponential population

growth is:

dNdt rmaxN

Exponential GrowthExponential

population growth results in a J-shaped curve.

Exponential GrowthThe J-shaped curve of exponential growth

is characteristic of some populations that are rebounding.

Exponential GrowthThe 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 GrowthExponential 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 GrowthA 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 ModelIn the logistic growth model, the per capita

rate of increase declines as carrying capacity is reached.

The Logistic Growth ModelThe logistic growth equation includes K,

the carrying capacity.

dNdt

(K N)Krmax N

The Logistic Growth ModelThe 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 SelectionK-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 GrowthWhat 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 GrowthAbiotic 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 EcologyCommunity ecology examines the interactions

among the various populations in a community.

InteractionsPopulations of

animals that form a community can interact in various ways.Beneficial for

one, negative for the otherPredation,

Parasitism, Herbivory

InteractionsBeneficial for one, neutral for the other

CommensalismBarnacles growing on whales

InteractionsBeneficial for both

Mutualism

InteractionsCompetition 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 CyclesMany

populations undergo regular boom-and-bust cycles.

These cycles are influenced by complex interactions between biotic and abiotic factors.

PredationPredation 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 ColorationCryptic coloration, or camouflage

makes prey difficult to spot.

Aposematic ColorationAposematic

coloration warns predators to stay away from prey.

MimicryIn some cases, one prey species may gain

significant protection by mimicking the appearance of another.

Batesian MimicryIn Batesian mimicry, a palatable or

harmless species mimics an unpalatable or harmful model.

Müllerian MimicryIn 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 SpeciesKeystone species are not necessarily

abundant in a community.They exert strong control on a community by their

ecological roles, or niches.

Keystone SpeciesField studies of sea stars exhibit their

role as a keystone species in intertidal communities.

Keystone SpeciesObservation of

sea otter populations and their predation shows the effect the otters have on ocean communities.

EcosystemsAn ecosystem consists of all the organisms

living in a community as well as all the abiotic factors with which they interact.

EcosystemsEcosystems can

range from a microcosm, such as an aquarium to a large area such as a lake or forest.

EcosystemsRegardless of an ecosystem’s size, its dynamics

involve two main processes:Energy flowChemical cycling

Energy flows through ecosystems, while matter cycles within them.

Trophic RelationshipsEnergy and

nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores).

Trophic LevelsPrimary production in an ecosystem is the

amount of light energy converted to chemical energy by autotrophs during a given time period.Photosynthesis

Trophic LevelsConsumers include:

Herbivores – animals that eat plants.Carnivores – animals that eat other animals.Decomposers – feed on dead organic matter.

Trophic LevelsDecomposition

connects all trophic levels.

Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs.

Energy FlowEnergy 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 TransferThe 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 ProductionThis 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 BiomassMost biomass pyramids show a sharp

decrease at successively higher trophic levels.Occasionally inverted

Nutrient CyclingLife 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 EnvironmentHumans 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 EnvironmentIn 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 SpeciesAn 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 ServicesEcosystem 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 speciesOverexploitationDisruption of “interaction networks”

ExtinctionHabitat fragmentation increases local extinction

and speciation.

Species that have larger ranges or better dispersal abilities are better protected from extinction.

ExtinctionThere have been five mass extinctions.

Each time a large percentage of the species on earth went extinct.