Animal Ecology

Chapter 2

Ecology

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Ernst Haeckel introduced the term ECOLOGY defined as the relation of animal to its organic as well as inorganic environment.

The Hierarchy of Ecology

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Organism Population Community Ecosystem Biosphere

The Hierarchy of Ecology

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Organism: Is the base of the ecological hierarchy.

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Population: a group of animals coexist with others of the same species.

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Community: Populations of different species co-occur in more complex associations.

Communities

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The complexity of a community is measured as species diversity.

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Species diversity: is the number of different species that coexist to form the community.

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Predation, competition, parasitism, and mutualism.

The Hierarchy of Ecology

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Ecosystem: An ecosystem consists of all populations in a community together with their physical environments.

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Biosphere: The largest ecosystem.

Environment and Niche

Environment and Niche

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Environment: includes the abiotic (nonliving) factors, and biotic (living) factors.

Environment and Niche

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Environment: includes the abiotic (nonliving) factors, and biotic (living) factors.

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Niche: a multi dimensional relationship of species with its environment.

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Fundamental niche: is the potential niche Realized niche: the subset of potentially suitable environments that an animal actually experiences.

Figure 2.2 p 37

Populations

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Population: a reproductively interactive group of animals of a single species

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A species may be a single, cohesive population or may contain many geographically disjunct populations, often called demes.

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Members of a deme interbreed, and therefore share a common gene pool.

Metapopulation

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Refers to a population subdivision into multiple genetically interacting demes.

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Gene flow can be symmetrical or asymmetrical

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In asymmetrical demes you can have source and sink demes

Population Demography

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Age structure: cohort and survivorship Sex ratio: sexual reproduction, cloning, unitary, parthenogenesis

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Growth Rate

Survivorship

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Cohort: individuals born at the same time.

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Survivorship: measures the survival of individuals in a population from birth to death of the last member of a cohort.

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There are three principle types of survivorship curves, they are referred to as I, II, and III.

Figure 2.4 p 39

Birds Inverts, fish, frogs Figure 2.4 p 39

Birds Inverts, fish, frogs Humans Figure 2.4 p 39

Population Age Structure

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Some animals such as insects and many invertebrates reproduce only once before they die.

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Other animals such as mammals and many vertebrates survive long enough to reproduce multiple times.

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These groups of animals exhibit age structure.

Figure 2.5 p 39

Population Growth and Intrinsic Regulation

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Population growth = birth rate – death rate.

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All populations have an inherent ability to grow exponentially, this is the intrinsic rate of increase (r).

Population Growth and Intrinsic Regulation

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Although all populations have an inherent ability to grow exponentially, there are limited resources in the environment.

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These limited resources in the environment create a carrying capacity (K) on populations of animals.

Figure 2.6 p 40

Carrying Capacity

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In reality populations of animals fluctuate around the carrying capacity, these are known as oscillations.

Figure 2.7 p 41

Why do populations Oscillate around the K?

Why do populations oscillate around the K?

1) The carrying capacity of an environment can change over time.

Why do populations oscillate around the K?

1) The carrying capacity of an environment can change over time.

2) Animals always experience a lag between the time that a resource becomes limiting and the time that the population responds by reducing its rate of growth.

Why do populations oscillate around the K?

1) The carrying capacity of an environment can change over time.

2) Animals always experience a lag between the time that a resource becomes limiting and the time that the population responds by reducing its rate of growth.

3) Extrinsic factors (other biotic and abiotic factors).

Figure 2.7 p 41

Extrinsic Limits of Population Growth

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Two Types of Extrinsic Factors

Extrinsic Limits of Population Growth

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Two Types of Extrinsic Factors

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Density-independent: these are abiotic limiting factors (frost kills all the mosquitoes)

Extrinsic Limits of Population Growth

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Two Types of Extrinsic Factors

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Density-independent: these are abiotic limiting factors (frost kills all the mosquitoes)

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Density-dependent: These are biotic limiting factors (competition, predators and parasites)

Community Ecology

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Populations of animals that form a community interact in three ways.

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Detrimental (-)

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Beneficial (+)

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Neutral (0)

Types of interactions

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Predator/prey and parasite/host (+,-), coyote/rabbit; tapeworm/coyote.

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Commensalism (0,+), pilot fishes and remoras with sharks.

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Mutualism (+,+) termites and gut protozoa.

Competition

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Sometimes competition between species reduces fitness of both species, (-,-).

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Sometimes the effect on one species in a competitive relationship is negligible, (0,-) amensalism or asymmetric competition. (eg. Barnacles)

Competition

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Usually in nature competition is more complex when more than two species are competing for resources.

Competition and character displacement

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Competition only occurs when two or more species share a LIMITING resources not just sharing resources.

Competition and character displacement

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Niche overlap: the portion of resources shared by the niches of two or more species.

Competition and character displacement

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Niche overlap: the portion of resources shared by the niches of two or more species.

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Competitive exclusion: strongly competing species cannot coexist indefinitely.

Competition and character displacement

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Niche overlap: the portion of resources shared by the niches of two or more species.

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Competitive exclusion: strongly competing species cannot coexist indefinitely.

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In order to coexist in the same habitat, species must specialize by partitioning a shared resource, this is known as character displacement.

Figure 2.10 p 44

The ghost of competition past

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The absence of competition today.

Guilds

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When several species share the same general resource by partitioning resources they are known as a guild.

Robert MacArthur

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Studied five species of warblers in spruce woods of the northeastern U.S.

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The five species of birds look vary similar in size and appearance.

Robert MacArthur

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Studied five species of warblers in spruce woods of the northeastern U.S.

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The five species of birds look vary similar in size and appearance.

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How can they coexist?

Figure 2.11 p 45

Predators and Parasites

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Predators and prey and parasites and hosts to some degree cause coevolution.

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Predators get better at catching prey and prey get better at escaping predators.

Predators and Parasites

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Most predators feed on more than a single species.

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However, when a predator relies primarily on a single prey species, both populations tend to fluctuate cyclically.

Figure 2.12 p 45

Predator Prey Interactions Defenses by potential prey

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Distasteful prey and warning coloration.

Defenses by potential prey

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When palatable prey adopt warning coloration this is an advantage for the prey and deceit for the predator.

Defenses by potential prey

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Batesian mimicry: Palatable prey can deceive potential predators by mimicking distasteful prey.

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Müllerian mimicry: Two or more toxic species resemble each other.

Figure 2.13 p 46

Keystone Species

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An influential species on other species that if it is absent it drastically changes an entire community.

Figure 2.14 p 47

Ecosystems

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Transfer of energy and materials among organisms within ecosystems is the ultimate level of organization in nature.

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Productivity: incorporation of material and energy into biological systems.

Trophic Levels and Food Webs

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Primary Producers: fix and store energy from outside the ecosystem (photosynthetic organisms).

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Consumers: herbivores eat plants directly; decomposers bacteria and fungi.

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Carnivores: eat other animals.

Figure 2.15 p 49

Food chains in terms of Pyramids

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Ecological pyramids or Eltonian pyramids: depict numbers of organisms transferred between each trophic level. Units can be numbers, biomass or energy.

Fig. 2.16 p 51

Nutrient Cycles

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All elements essential for life are derived from environmental air, soil, rocks, and water (nutrients).

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These nutrients are released and returned to the environment when the organism dies.

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Therefore nutrients flow in a perpetual cycle between biotic and abiotic components of an ecosystem, this is called a biogeochemical cycle.

Figure 2.17 p 52 Nutrients recycled, energy flow is one way!

The Big Picture

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Ecology is the study of living organisms and their interactions with the environment and other living organisms.

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Ecology has a hierarchy of organization.

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Different types of interactions occur at the population, community or ecosystem level.