1. Chapter 2
Animal Ecology

2. Chapter opener 02

3. Ecology Definition Ecology
Study of the relationship of organisms to their environment

4. Ecology
Necessary to understand the physiological and behavioral mechanisms of organisms to understand their ecological relationships
Animals in nature coexist with others of the same species as reproductive units are called populations
Population has properties that cannot be discovered by studying individuals alone
Populations of many species live together in complex communities
The number of different species present in a community is measured as species diversity

5. Ecology
Many species interact with each other such as predation, parasitism, competition
Predators obtain energy and nutrients by killing and eating prey
Parasites drive similar benefits but do not kill the host
Parasitoid is a parasite that kills its host organism
Competition occurs when resources become limited
Mutualism occurs when both members of a pair of species benefit from their interactions, usually avoiding negative interactions with other species
Larger units or ecosystems allow study of the community and the physical environment
Biosphere is the land, water, and atmosphere that envelops the planet and supports all life on earth

6. Ecology Environment and the Niche Abiotic factors (nonliving)
Space, energy forms including sunlight, heat, wind and water currents, and the soil, air, water and chemicals
Biotic factors (living)
Include other organisms as food, or competitors, predators, hosts or parasites
Resources
Environmental factors that an animal uses directly

7. Ecology Some resources are expendable
Food, once eaten, is no longer available and must be continuously replenished
Space is not consumed by being used and is therefore nonexpendable
Habitat
Physical space where an animal lives and is defined by the animal’s normal activity

8. Ecology Niche The life requirements of an organism define its niche
A niche includes the animal’s limits of temperature, moisture, food, and other factors
Addition of important factors such as salinity or pH describes a complex multidimensional niche
The niche of a species undergoes evolutionary changes over successive generations

9. Ecology Some animals are generalists Other animals are specialists
Wide niches
Can tolerate a wide range of salinity or eat a wide range of foods
Other animals are specialists
Have narrow dietary requirements or limited tolerance to temperature changes, etc.
Fundamental niche
Describes animal’s potential role to live within a wider range of conditions
Realized niche
The narrower subset of suitable environments that an animal actually experiences

10. Hierarchy of Ecology Populations Population Factors
A population is a reproductively interactive group of animals of a single species
A geographically and genetically cohesive population that is separable from other such populations is a deme
Share a gene pool
Movement among demes provides some evolutionary cohesion among species

11. Ecology Local environments may change unpredictably
Can cause a local deme to become depleted or eliminated
Immigration
Source of replacement among demes within a region
Interaction among demes in this manner called metapopulation dynamics

12. Ecology
Survivorship Curves define the age pattern of a population from birth to death of the last member
Type I Survivorship Curve
All individuals die at the same time, occurs rarely in nature
Type II Survivorship Curve
Rate of mortality as a proportion of survivors is constant across ages
Characteristic of birds that care for their young
Humans fall between Type I and Type II depending on nutrition and medical care
Type III Survivorship Curve
Represents many species that produce huge numbers of young but experience rapid and sustained mortality
Explains the need for high reproductive output of many animals

15. Ecology
Semelparity is the condition in which an organism reproduces only once during its life history
Iteroparity is the condition in which an organism reproduces mutiple cohorts of offsprings that may mature and reproduce while their parents are still alive and reproductively active
Populations of animals containing multiple coherts such as robins, box turtles, and humans exhibit age structure

16. Ecology Population growth
Difference between rates of birth and death
Populations have the ability to grow exponentially at the intrinsic rate of increase (r)
Forms a steeply rising curve
Unrestricted growth is not prevalent in nature
Growing population eventually exhausts food or space
Planktonic blooms and locusts outbreaks both end when resources are exhausted

17. Ecology Among many resources, one will be depleted first
Limiting resource
The largest population that the limiting resource can support is the carrying capacity (K)
A population slows growth rate in response to diminishing resources

20. Ecology Carrying Capacity of the Human Species
Humans have the longest record of exponential population growth
About 5 million around 8000 BC before the Agricultural Revolution
Human population rose to 500 million by 1650
1 billion by 1850
2 billion by 1927
4 billion by 1974
6 billion by October 1999
Will reach 8.9 billion by 2040
Food production cannot keep pace with exponential population growth indefinitely

21. Ecology Extrinsic Limits to Growth Density-independent Factors
Abiotic factors reduce populations by floods, fires, storms and severe climate fluctuations
These agents kill young or other members of a population regardless of the size of population
Cannot truly regulate population growth because they are unrelated to population size

22. Ecology Density-dependent Factors
Biotic factors that respond to density of the population
Include predators and parasites
As a population increases in number and individuals live closer together
Effects of parasites and disease are more severe
Competition between species for a common limiting resource
Lowers the effective carrying capacity for each species

23. Community Ecology Interactions Among Populations in Communities
In a community, populations of different species interact
The number of species that share a habitat
Known as species diversity
Species interactions may benefit or harm the species involved
In a predator-prey interaction
Predator benefits and the prey is harmed
Parasitism benefits the parasite and harms the host
Herbivory benefits the animal and harms the plant

25. Community Ecology In commensalism
One species benefits and the other neither benefits nor is harmed
Some mutualistic relationships become obligatory mutualism
Neither can survive without the other
Competition between two species
Reduces the fitness of both
Asymmetric competition (amensalism) affects one species less than the other

27. Community Ecology Competition and Character Displacement
Competition occurs when two or more species share a limiting resource
If resource is not in short supply
Sharing the resource does not demonstrate competition
Niche overlap
Portion of the niche’s resources that are shared by two or more species

28. Community Ecology Competitive exclusion
Principle that no two species will occupy the same niche for a long time
Eventually one will exclude the other
To coexist, two species can specialize by partitioning a shared resource
Specialization involves character displacement
Differences in organismal morphology or behavior related to exploitation of a resource
They do not compete with each other directly

30. Community Ecology Where two species coexisted
Competition between them led to evolutionary displacement to diminish the competition
When two or more species reduce niche overlap to share the same general resources, they form a guild

32. Community Ecology Predators and Parasites
Many animals and plants are in co-evolutionary relationships
Each in a race with the other
If a predator relies primarily on a single prey species
Populations tend to fluctuate cyclically with each other
Predator-prey relationship
Led to development of mimicry
Harmless species mimic models that have toxins or stings

35. Community Ecology
Another mimicry complex consists of many different species, all with noxious or toxic factors, that evolve to resemble each other
A keystone species is so pervasive to a community that its absence drastically changes the entire community
Keystone species reduce competition and allow more species to coexist on the same resource
Periodic natural disturbances also allow more species to coexist in diverse communities

37. Community Ecology Ectoparasites Endoparasites
Host provides nutrition from its body and aids dispersal of parasite
Endoparasites
Lost ability to choose habitats
Must have tremendous reproductive output to ensure offspring will reach another host
Coevolution between parasite and host is expected to generate an increasingly benign, less virulent relationship if host organisms are uncommon and/or difficult for a parasite to infest
Death of the host also ends or shortens a parasite’s life
Exceptions occur when alternative hosts are available

38. Ecosystems Trophic Levels Primary producers Herbivores Carnivores
green plants or algae, fix and store energy from sunlight
Herbivores
First level of consumers that eat plants
Carnivores
Feed on herbivores or other carnivores
Decomposers
Mainly bacteria and fungi
Break dead organic matter into mineral components for reuse by plants to start the cycle over again

40. Ecosystems Energy Flow and Productivity
Every organism has an energy budget and must obtain enough energy to grow, reproduce, etc.
Gross productivity (Pg)
Total energy assimilated or taken in
Some used to maintain metabolism
Net productivity (Pn)
Energy stored in the animal’s tissue as biomass
Available for growth of the animal and for reproduction

41. Ecosystems Energy is limited and can be represented as
Pn = Pg - R where R is respiration
Energy budget of every animal is finite
Much energy is lost when it is transferred between trophic levels in food webs
More than 90% of the energy in an animal’s food is lost as heat
Less than 10% is stored as biomass
Each trophic level contains only 10% of the energy of trophic level below it

42. Ecosystems Ecological Pyramids Eltonian pyramid Pyramid of biomass
Based on numbers of organisms at each trophic level
Does not indicate mass of organisms at each level
Pyramid of biomass
Total bulk or “standing crop” of organisms at each trophic level
Energy pyramids
Depicts rate of energy flow between levels
Never inverted
Amount of energy transferred from each level is less than what entered it
Gives best overall picture of community structure because it is based on production

44. Ecosystems Life Without the Sun
From 1977 to 1979, dense communities were first discovered on sea floor thermal vents
Producers in the vent communities are chemoautotrophic bacteria that oxidize hydrogen sulfide
Tubeworms and bivalve molluscs form trophic communities that rely on this non-photosynthetic source of nutrients

45. Ecosystems Nutrient Cycles
Decomposers feed on remains of animals and plants and on fecal material and return substances to the ecosystem
Biogeochemical cycles involve exchanges between living organisms, rocks, air and water
Continuous input of energy from sun keeps nutrients flowing and the ecosystem functioning
Synthetic compounds challenge nature’s nutrient cycling

47. Ecosystems Pesticides in food webs
May be concentrated as they travel up through succeeding trophic levels
Kills non-target species
Some chemicals remain in the environment for long periods of time
Genetic engineering of crop plants aims to improve resistance to pests and lessen the need for chemical pesticides

48. Extinction and Biodiversity
Rates of speciation slightly exceed rates of extinction
Approximately 99% of all species that have ever lived are extinct
Extinction events killing at least 5% of existing species have occurred almost continuously throughout geological time
Human activity clearly has induced numerous species extinctions
Humans must avoid making the present time rival the great extinction crises of earth’s geological history