BIO 103
Jean2979
Animal_Diversity_8e_Ch_02.pptxChapter 2
Animal Ecology
Talkeetna Mountain Range, Alaska
©Cleveland P. Hickman, Jr.
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Ecology
Definition
Ecology
Study of the relationship of organisms to their environment
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Populations and Communities
Must understand the physiological and behavioral mechanisms of organisms in order 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 ecological communities
The number of different species present in a community is measured as species richness
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Behavioral Temperature Regulation
Ecological Interactions
Species interact with each other in many ways
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
Larger units, ecosystems, allow study of the ecological community and the physical environment
Biosphere is the land, water, and atmosphere that envelops the planet and supports all life on earth
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Environment and the Niche
The environment comprises all conditions that directly impact an animal’s chances for survival and reproduction
The environment includes
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
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Resources and Habitat
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
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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
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Three-Dimensional Niche
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Organism Tolerances
Some animals are generalists
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
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Populations
Animals exist in nature as members of populations
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
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Metapopulation Dynamics
Interaction among demes is called metapopulation dynamics
Local environments may change unpredictably
Can cause a local deme to become depleted or eliminated
Migration is source of replacement among demes within a region
Stable demes (source demes) supply emigrants to the less stable demes (sink demes) that are susceptible to extinction
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Demography
Demography is the study of the age structure, sex ratio, and growth rate of a population
Some organisms are modular
Consist of colonies of genetically identical organisms
Reproduce via asexual cloning or fragmentation
Sponges, corals, and bryozoans
It is easier to count and measure individual or unitary animals than colonial organisms
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Survivorship Curves
Survivorship curves describe the survivorship pattern of a species from birth to death of the last member of a generational cohort
Type I Survivorship Curve
All individuals die at in old age, 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
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Three Survivorship Curves
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Reproductive Patterns
Semelparity is the condition in which an organism reproduces only once during its life history
Iteroparity is the condition in which an organism reproduces multiple cohorts of offspring
Offspring may mature and reproduce while their parents are still alive and reproductively active
Populations of animals containing multiple cohorts (such as robins, box turtles, and humans) exhibit age structure
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Age Structure
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Population Growth
Population growth is the 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
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Regulation of Population Growth
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
Sigmoid growth occurs when population density exerts negative feedback on growth rate
Known as density dependence
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Exponential and Logistic Growth
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Growth Curves
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Human Population Growth
Humans have the longest record of exponential population growth
Agriculture increased the carrying capacity
About 5 million around 8000 BC before 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
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Density-Independent Factors
Density-independent factors
Abiotic factors that reduce populations (floods, fires, storms, severe climate fluctuations, etc.)
These agents kill members of a population regardless of the size of population
Cannot truly regulate population growth because they are unrelated to population size
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Density-Dependent Factors
Density-dependent factors
Biotic factors that respond to density of the population (predators and parasites)
As population increases in number and individuals live closer together effects of these biotic factors are more severe
Populations regulated by predation and parasitism are not limited by resources
Competition between species for a common limiting resource lowers the effective carrying capacity for each species
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Interactions Among Populations
In a community, populations of different species interact
Species interactions may be beneficial , detrimental , or neutral (0)
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
In commensalism one species benefits and the other neither benefits nor is harmed
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Commensalism
©Noble Proctor/Science Source
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Mutualistic Relationships
In mutualism both species benefit from their interaction
Some mutualistic relationships become obligatory mutualisms
Neither can survive without the other
Facultative mutualisms are interactions that are not required for a species to survive
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Mutualism
©Cleveland P. Hickman, Jr.
©Cleveland P. Hickman, Jr.
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Competition
Competition between two species reduces the fitness of both
Often considered the most common and important type of interaction
Asymmetric competition (amensalism) affects one species less than the other
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Competition and Niche Overlap
Competition occurs when two or more species share a limiting resource
If resource is not in short supply then sharing the resource does not demonstrate competition
Niche overlap is the portion of resources that are shared by two or more species
Reducing niche overlap reduces conflict between competing species
Competitive exclusion is the principle that no two species will occupy the same niche for a long time
Eventually one will exclude the other
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Resource Partitioning
To coexist, two species can specialize by partitioning a shared resource (resource partitioning)
Often involves differences in organismal morphology or behavior related to exploitation of a resource
Ecological character displacement
Microhabitat selection is also a common method of resource partitioning
They do not compete with each other directly since preferred microhabitats are distinct
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Darwin’s Finches
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Guilds
When two or more species share the same general resources, they form a guild
If those species occur in the same area, theory of competitive exclusion predicts they will exhibit resource partitioning
Classic example is MacArthur’s study of warblers in spruce forest
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Warbler Feeding Guild
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Predator-Prey Evolution
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
Longest documented natural example is cycle between snowshoe hares and lynx in Canada
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Predator-Prey Cycles
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Prey Defenses
Potential prey evolve defenses against predators
Cryptic defenses – bodies match some aspect of environment
Aposematic defenses – bright colors or behavior warn predators of inedibility
Batesian mimicry – harmless species mimic models that have toxins or stings
Müllerian mimicry – many different species, all with noxious or toxic factors, that evolve to resemble each other
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Mimicry
©Nuridsany et Perennou/Science Source
©John Keates/Alamy Stock Photo
©Bill Brooks/Alamy Stock Photo RF
©Arthur C. Twomey/Science Source
©Mark Newman/Lonely Planet Images/Getty Images
©Bill Brooks/Alamy Stock Photo RF
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Keystone Species
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
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Keystone Species Removal
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Parasites
Ectoparasites – host provides nutrition from its body and aids dispersal of parasite
Endoparasites – have 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
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Trophic Levels
Ecosystem productivity is divided into trophic levels based on how organisms obtain energy and materials
Primary producers
green plants or algae, fix C and N, store energy (usually 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
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Food Web
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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
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Energy Flow and Productivity
Every organism has an energy budget and must obtain enough energy to grow, reproduce, etc.
Energy budget has three main components
Gross productivity - total energy assimilated or taken in (most used to maintain metabolism)
Net productivity – energy stored in the animal’s tissue as biomass; some is used for growth and reproduction
Respiration (R) – energy used for metabolic maintenance
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Laws of Thermodynamics
Energy is limited and can be represented as
Energy budget of every animal is finite
Energy is only available for growth after satisfying maintenance needs
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
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Ecological Pyramids
Ecological pyramids represent food chains in terms of numbers or biomass
Eltonian pyramid - based on numbers of organisms at each trophic level
Does not indicate mass of organisms at each level
Pyramid of biomass – show total bulk or “standing crop” of organisms at each trophic level
Energy pyramids - depict rates of energy flow between levels
Never inverted since 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
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Three Ecological Pyramids
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Nutrient Cycles
All essential elements come from the environment
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
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Energy Flow and Nutrient Cycles
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Pesticides and Genetic Engineering
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
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Biodiversity and Extinction
Rates of speciation slightly exceed rates of extinction
Approximately 99% of all species that have ever lived are extinct
Extinction events killing at least 30% of existing species have occurred, on average, every 10 million years
Extinction events killing at least 65% of existing species (mass extinctions) have occurred, on average, every 100 million years
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Mass Extinctions
Table 2.1 Comparison of Species Extinction Levels for the Big Five Mass Extinctions*
| Extinction Episode | Age, Myr Before Present | Percent Extinction |
| Cretaceous | 66 | 76 |
| Triassic | 200 | 76 |
| Permian | 251 | 96 |
| Devonian | 359 | 82 |
| Ordivician | 443 | 85 |
*After David Raup (1995), with revised dates for these extinctions.
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Human Impacts on Biodiversity
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
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Appendix of Image Long Description
Behavioral Temperature Regulation Long Description
In the morning a lizard absorbs sun to heat up without exposing too much of the body. At midday a lizard seeks shade to avoid overheating. In late afternoon a lizard basks in the sun.
Three Survivorship Curves Long Description
The x-axis is time, the y-axis is percent of surviving individuals on a log scale. A Type I curve has high survivorship until old age when the population dies. A Type II curve has a consistent decrease in survival over time. A Type III curve has a large decrease in survival early in life, then constant survival over time.
Age Structure Long Description
In 1975 most of the population is youthful, with only a small percentage over the age of 60. By 2005 the distribution of people across age classes has become much more even.
Growth Curves Long Description
Growth curve for sheep introduced onto island is exponential at first, then fluctuates regularly around carrying capacity.
Growth curve for ring-necked pheasant on an island oscillates greatly.
The global human population growth curve is still increasing exponentially.
Darwin’s Finches Long Description
Three finch species occur on Santa Cruz Island with varying beak depth. G. fulginosa has the shortest, G. magnirostra the longest, and G. fortis is in the middle. Only G. fulginosa occurs on Los Hermanos Island, and its beak depth is slightly greater than on Santa Cruz Island. Only G. fortis occurs on Daphne Island, and its beak depth is slightly smaller than on Santa Cruz Island.
Warbler Feeding Guild Long Description
The five wood warbler species partition the tree by selecting different microhabitats. The Cape May warbler forages in the outer branches at the top of the tree. The black-throated green warbler forages on the outer and inner branches in the top half of the tree. The Bay-breasted warbler forages in the middle section of the tree. The Blackburnian warbler forages on branches close to the trunk. The warbler on the inner branches close to the trunk. The Yellow rumped warbler forages in the lower portion of the tree.
Mimicry Long Description
Harmless moth mimics a yellowjack wasp.
Distasteful Neotropical butterflies have similar coloring.
Distasteful viceroy butterfly mimics the coloration of the toxic monarch butterfly.
Keystone Species Removal Long Description
The removal of sea stars from an intertidal community results in the mussel outcompeting other species and covering both the lower and middle intertidal zones.
Three Ecological Pyramids Long Description
Pyramid of numbers depicts a decreasing number of organisms with increasing trophic level.
Pyramid of biomass for a freshwater stream has a similar structure, but that of the English Channel is an inverted pyramid.
Pyramid of energy depicts a decreasing amount of available energy with increasing trophic level.
Energy Flow and Nutrient Cycles Long Description
Energy flows from the sun through organisms, with some leaving the earth as respiratory losses. Nutrients flow from the atmosphere through organisms and the soil nutrient pool and back to the atmosphere again.
