chapter 45: population and community ecology - BIOL 2130

population

a group of the same species in the same area with the potential to interact with each other

• fluctuation depending on

  • seasonal changes

  • competition for resources

  • effects of natural disasters

  • climate change

• demographics (math models to study dynamics) predict changes in responses to changes in ecosystem

• size (total number of individuals) and density (number of inidividuals within predetermined area) = make predictions

  • describes at particular points n time 

quadrat

measures populations of immobile organisms

• makes artificial boundaries (boxing out a small section of a habitat)

• consider organism size and distribution

• count individuals within box

• measures density 

• ex: counting number of flowering species in one box  

mark and recapture

measures populations of mobile and larger organisms

• tags, bands, paint, body markings

• ratio of marked vs unmarked = predicts population size 

• (number of marked first catch x total number of second catch) / number marked second catch = N

• limits: learned avoidance/approach behavior, potential harm during capturing

species distribution

shows how individuals interact with each other

uniform: evenly distributed 

• abundant, wide

• some plants and territorial species (ex: penguins, nesting birds)

• due to competition or territorial behavior

random: groups and/or singular individuals distributed inconsistently

• wind dispersed plants (ex: dandelions)

• resources are consistent and interactions are minimal

clumped: gathered in one area

• plants that drop seeds and species that live in family groups

• function of habitat niche availability

• most common, social behavior or patchy resources

demography

statistical study of population changes over time

• birth rates, death rates, life expectancies

• each measure has effect on population size and density

  • female-biased sex ratio

  • age structure

• influences how populations grow or decline over time

• life tables

• mortality rate = (number of inds dying / number of inds surviving) x 1000

life tables

calculate life history

• age interval, number dying, number surviving, mortality rate, life expectancy

• as individuals age, the number dying increases due to being more vulnerable

• life expectancy decreases since fewer individuals survive at older ages

survivorship curves

compares life history

• individuals surviving / percentage of max life expectancy on log scale

• type 1: small clutch, high parental care (ex: humans)

• type 2: small/med clutch size, moderate parental care (ex: birds)

• type 3: large clutch size, little to no parental care (ex: trees)

exponential

population growth model of a population with unlimited resources

• displays accelerating growth rate

• number organisms added in each generation

• J shape

• abundance of resources

• ex: bacteria

logistic

population growth model represents a population “struggling for existence” due to limited resources

• DOES NOT account for unpredictability of env and abiotic factors

• carrying capacity K: max population size the env can support, size fluctuates around it over time 

  • exponential then plateaus (levels off)

• would assume individuals have equal opportunity to obtain resources

• but intraspecies competiton means more are suited to survive than others

• competition increases as population size increases

• S shape

• ex: wild animals

nature

regulates population growth and carrying capacity

• density dependent factors

• density independent factors

• humans impact communities to spread out by consuming their resources

• humans also themselves are impacted by these factors

density dependent

population regulation where density at a given time affects growth and mortality rates

• most are biotic factors: predation (both sides), competition, waste accumulation, disease

• influences reproductive: stress and resource scarcity, inbreeding

• influences mortality

density independent

population regulation where regardless of population density, it will influence mortality

• typically abiotic factors: weather, fire, pollution

• interacts with dependent factors

• population recovery — may be more susceptible to competition, inbreeding, limited resources bc of small number of individuals

life history

species reproductive strategies, habitat, behavior, and the way they obtain resources and care for their young

• k selected

• r selected

k selected

species history with stable, predictable environments

• exist close to carrying capacity (K) = HIGH intraspecies competition

• few, large, long gestation during reproduction

• young are dependent at birth

• HIGH parental care

• mature late

• ex: elephant, one calf at a time

r selected

species history with unpredictable, changing environments

• decreased intraspecies competition

• many, small, short gestation during reproduction

• young are independent at birth

• little to NO parental care

• ex: frog, lays thousands of eggs

community ecology

• predation and herbivory

• competition exclusion principle

• symbiosis

• role of species in the ecosystem

predation and herbivory

drives adaptation!

predator and prey relationships vary over time

• ex: lynx and hare

• as prey increases, predator number rises, then both decline 

some plants developed defense adaptations against herbivory

• physical: thorns, spines, camoflage

• chemical: skunk spray, toxins

• other plants encourage it (mutualism): flowers and fruit with pollinators

mimicry

batesian: harmless species mimic warning colors of a harmful one

• ex: many insects mimic wasps/bees

mullerian: many species with defenses share coloration

• ex: bees and wasps share yellow-black patterns

competitive exclusion principle

two species CANNOT occupy the same niche in a habitat

• a niche includes all resources needed to survive

• similar species must reduce direct competition: evolve to occupy slight diff space, consume diff food, or use diff shelters

• ex: different species of birds inhabit diff parts of a tree

symbiosis

close interactions between individuals of different species over an extended period of time, impacting abundance and distribution of associating populations 

• commensalism: one benefits, other is not harmed (ex: barnacles on a whale)

• mutualism: both species benefit (ex: bees and flowers

• parasitism: one species benefits, other is harmed (ex: ticks and mammals)

foundation species

typically primary producers to bring energy into a community

• great impact on community structure

• ex: plants

keystone species

species that are key to maintain biodiversity within a community

• removal causes major changes or even a collapse of an ecosystem!

• regulates population sizes

• predators or mutualists

• ex: wolves in yellowstone 

biodiversity

a communities biological complexity, including variety and balance pf species

• species richness: # of species in a particular habitat, influenced by latitude

  • greatest richness for mammals in NA and SA located near equator 

  • higher productivity, more stable climate

• relative abundance: species evenness throughout a habitat

  • foundation species typically have highest (ex: coral, kelp, trees)

  • shape env and provide habitat/resource

community dynamics

changes in community structure and composition over time

• primary succession: starts in lifeless area with NO soil (ex: on a volcanic island)

• secondary succession: previous community was disturbed, soil remains (ex: after a forest fire)