Chapter 2: Animal Ecology

Ecology: The relation of the animal to its organic as well as inorganic environment.

• Introduced by Ernst Haeckel (German zoologist) in the mid-19th century

  

<<Environment and the Niche<<

An animal’s environment comprises all conditions that directly affect its chances for survival and reproduction.

• Conditions/factors:

  • Abiotic
  • Space (habitat)
  • Forms of energy (sunlight, heat, wind, and water currents)
  • Materials (soil, air, water, chemicals)
  • Biotic
  • Other organisms
  • Prey, predators, competitors, hosts, mutualists, parasites

• Niche

  • The role of an organism, population, or species in an ecological community
  • Components:
  • Resource usage
  • Unique way of life
  • Relationship to other abiotic and biotic factors
  • Subject to evolution by natural selection
  • Undergoes changes over successive generations

  1. Fundamental Niche

  • Variety of potential roles an organism or population in an ecological community could perform

  2. Realized Niche

  • The role actually performed by an organism or population in its ecological community at a particular time and place

<<Populations<<

Animals exist in nature as members of populations, or reproductively interactive groups of animals of a single species.

• Deme: Geographically and genetically cohesive populations that are separated from other populations
  • Regularly interbreed + share a common gene pool
  • Each has its own characteristic demographics
• Demography = the study of a population’s properties and factors that influence them
  • Sex ratio = accounting of the ages of individuals in a population at a particular time and place
  • Reveals whether the population is growing, stable, or declining
  • Growth rate
  • Age structure
• Animal species have different characteristic patterns of survivorship
  • The proportion of a population that persists from one point in their life history, such as birth, to another one, such as reproductive maturity or death
  • 3 principal types:
  • I: most die at old age
  • II: mortality rate is constant over all ages
  • III: infant or juvenile mortality is very high relative to that of young adults
• Most animals do not survive to reach reproductive age
  • Those that do exhibit:
  • Semelparity: Condition in which an organism reproduces only once during its life history
  • Iteroparity: Occurrence of more than one reproductive cycle in an organism’s life
• Population growth = birth rate – death rate
  • All populations have an inherent ability to grow exponentially if resources are unlimited
  • Exponential growth is not prevalent in nature
  • Limiting Factor: Resource in shortest supply relative to population needs
  • Carrying Capacity: The largest population that the limiting resource can support in a habitat

<<Community Ecology<<

Populations of animals that form a community interact in various ways

• Can be detrimental (-), beneficial (+), or neutral (0)

1. ^^Competition ( - / - )^^

   1. Two or more species compete for a limited resource
   2. Abundance of both species decreases

2. ^^Predation ( + / - )^^

   1. Predator abundance increases, prey abundance decreases

3. ^^Parasitism ( + / - )^^

   1. One species obtains nutrients from another species (host)
   2. Usually does not kill the host
   3. Parasite abundance increases, host abundance decreases

4. ^^Commensalism ( + / 0 )^^

   1. One species benefits, while the other is unaffected
   2. Often occurs when one species provides a home or transportation for another
   3. Benefitting species abundance increases, other species unaffected

5. ^^Mutualism ( + / + )^^

   1. Two species interact in a way that benefits both
   2. Abundance of both increases

<<Competition and Resource Partitioning<<

Competition: Members of the same species attempt to use resources that are in limited supply, but are necessary for survival.

• Result: not everyone has sufficient access to necessary resource(s)
• How to reduce: resource partitioning
  • Different resource required for different groups
  • Parents don’t compete with offspring
  • Similar species don’t compete with each other
  • E.g. different food for different age groups
• Selection of different microhabitats
  • Permits coexistence in the same tree
  • Feeding guild
  • Formed when several species share the same resources

<<Community Stability<<

Keystone Species: One on which the existence of a large number of other species in the community, and/or ecosystem, depends.

• Stabilize the community, help maintain its characteristics, and helps to hold its web of interactions together
• Examples:
  • Bats in tropical forests
  • Pollinators and seed dispersers
  • Without them, plants fail to reproduce
  • Sea otters in kelp forests
  • Eat sea urchins
  • Keeps population in check
  • Keeps urchins from eating too much kelp

<<Ecosystems<<

Species and the environment.

Ecological niche: The role the species plays in the community, its habitat, and its interactions with other species.

• One important aspect: Acquiring food
  • Autotrophs
  • Produce their own food for themselves, and all other members of a community
  • Take in CO2
  • Release O2
  • Producers
  • Photoautotrophs
  • Chemoautotrophs
  • Heterotrophs: Consumers
  • Need a source of organic nutrients
  • Release CO2 into the atmosphere
  • Types: Herbivores, Carnivores, Omnivores, and Decomposers (bacteria + fungi)
  • Detritus = dead organism + bacteria and fungi that are breaking down the wastes

<<Energy Flow in Ecosystems<<

The living components of ecosystems process energy and chemicals.

• Energy Flow: Begins when producers absorb energy

• Passing organic nutrients from one organism to another results in a loss of energy

  • When an herbivore eats a plant, a portion of the nutrients is used as an energy source
  • Eventually, energy dissipates into the environment as heat

• Visual representation: food web

• 2 types:

  • Grazing
  • Begins with plants
  • Detrital
  • Begins with bacteria and fungi

• Organisms are linked to one another based on feeding relationships

• Trophic Level

  • Level of nourishment within a food web
  • 1st level: producers
  • 2nd level: herbivores
  • 3rd level: carnivores
  • Energy is lost between levels
  • Only ~10% of energy from one level is available to the next level
  • This is why so few carnivores can be supported in a food web

  

<<Chemical Cycling in Ecosystems<<

Chemical Cycling: Begins when producers take inorganic nutrients from the environment.

• Biogeochemical Cycle

  • Pathways involve both living and nonliving components

• Carbon Cycle

  • Returns to and is withdrawn from the atmosphere as a gas
  • Organisms exchange CO2 with the atmosphere

• Terrestrial

  • Plants take up CO2
  • Incorporated into nutrients
  • Some returned to the atmosphere through respiration

• Aquatic

  • Indirect CO2 exchange with the atmosphere
  • CO2 combines with water (bicarbonate ion)
  • Source of carbon for algae

  

<<Biodiversity<<

Described in terms of the number of different species

• Currently: crisis

  • The number of extinctions expected to occur in the near future will, for the first time, be entirely attributable to human activities
  • Contributing Factors:
  • Habitat loss (85%) (Usually associated with sprawl of urban areas)
  • Introduction of exotic species (50%)
  • Water and air pollution
  • Overexploitation of natural resources (17%)

  ** in many cases, endangered species are threatened by multiple factors

People must understand that biodiversity is a resource of immense value.

• Directly AND indirectly
• Direct Values:
  • Medicinal value
  • Most prescription drugs in the US were originally derived from organisms
  • Examples:
    • Rosy Periwinkle (Madagascar)
    • Chemicals used to treat 2 types of cancer
    • The survival rate of childhood leukemia has gone from 10% to 90%
    • Hodgkin disease is now, usually, curable
    • Additional 328 types of drugs still in tropical forests, not yet found
    • Penicillin - derived from fungus
    • Immune cells in horseshoe crab blood
    • Detect bacterial contamination in vaccines and medical equipment

<<Indirect Values of Biodiversity<<

More economical to save ecosystems than individual species.

• Types:

1. Biogeochemical cycles

   1. Biodiversity within ecosystems keeps them balanced

2. Waste Disposal

   1. Decomposers break down organic wastes

3. Prevention of soil erosion

   1. Intact terrestrial ecosystems naturally retain soil

4. Climate Regulation

   1. At the local level: trees provide shade, block drying winds, and reduce the need for fans & AC
   2. Globally: forests regulate climate because they take up CO2

5. Ecotourism