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Chapter 53: Ecology

Terms in this set (19)

Population ecology
study of populations in relation to environment
population
- group of individuals of single species live in same general area.
- rely on same resources
- influenced by similar environmental factors
- interact and breed with one another
- described by boundaries and size (# of individuals)
density
number of individuals per unit area or volume (pop)
dispersion
pattern of spacing among individuals in geographic boundaries (pop)
mark-recapture method
sampling technique often use to estimate wildlife populations
- Individuals trapped and captured, marked w/ tag, recorded, and released.
- time elapsed, traps set again and individuals captured and identified.
- second capture yields marked and unmarked
- counts individuals, estimate total number of individuals in population.
- assumes marked same prob of being trapped as unmarked
- not safe assumption: trapped individuals may be more or less likely trapped 2nd time
Population density
- Add population: birth (reproduction) and immigration (new from other areas)
- remove individuals: death (mortality) and emigration (move out)
local densities
- Variations in characteristics
- show environmental and social interactions
- habitat more suitable than others.
- Social interactions between members maintain patterns of spacing
Dispersion, clumped
- individuals aggregate in patches
- Plants and fungi clumped where soil conditions favor germination and growth.
- Animal clump in favorable microenvironments (salamanders under fallen log) or facilitate mating interactions.
- Group increase effect of predators, such as wolf pack, and protection to prey
Dispersion, uniform
• when individuals are evenly spaced.
-ex. some plants secrete chemicals inhibit germination and growth of nearby competitors.
- ex. Animals territoriality, defense of bounded space against encroachment by others.
- rarer than clumped
random dispersion
- position of individuals in population independent of others,
- spacing unpredictable
- occurs in absence of strong attraction or repulsion among individuals or key physical or chemical factors homogeneously distributed
- ex. plants grow where windblown seeds land.
- uncommon
Demography
- study of vital stats of pop and how they change over time.
- interest are birth and death rates.
life table
age-specific summary of survival pattern of pop
- construct: follow fate of cohort, group of individuals of same age, from birth throughout lifetimes until dead
- researchers determine # of individuals that die in each age and calculate proportion of cohort surviving from 1 age to next
survivorship curve ( life table)
- plot of numbers or proportion of cohort of 1,000 individuals still alive at each age.
- Type I curve: flat at start, low death rate in early and middle life, and drops steeply as death rates increase older age (humans, less offspring)
- Type II curve intermediate, w/ constant mortality over life span (rodent, invertebrates, and annual plants show)
- Type III curve drops sharply at start, high death rates early life, but flattens as death rates decline for few (produce large # of offspring, little/ no care. ex. fish)
reproductive table
- age-specific summary of reproductive rates in pop
- constructed by measure reproductive outputs of cohorts from birth - death
- tallies # of female offspring each age group
- reproductive output females given age breed and # of female offspring of female
- Multiply # gives average # of female offspring
- vary greatly from species to species.
- high reproductive rate not lead to rapid pop growth unless conditions ideal for growth + survival
Change in population size
Change in population size = Births/ entering population + Immigrants/ leaving population − Deaths - Emigrants

- simplicity, ignore effects of immigration,emigration:
Change in population size = Births − Deaths
Exponential Population growth
- ideal conditions
- may assume max growth rate for pop (rinst), called intrinsic rate of increase
- dN/dt = rinstN
- increases at constant rate, J-shaped growth curve pop size over time
- max rate of increase constant, pop accumulates more new individuals per unit of time when large
- curve gets steeper over time.
- pop w/ high intrinsic rate of increase grows faster than 1 w/ lower rate of increase.
- J-shaped curves characteristic introduced into new environment or reduced by a catastrophic event and rebounding
carrying capacity(K)
- max stable pop size that environment can support
- not fixed but varies over space and time w/ limiting resources
- Energy, shelter, refuges from predators, nutrient, water, and suitable nesting sites, limiting.
- individuals can't obtain sufficient resources to reproduce, then per capita birth rate b declines.
- individuals cannot find and consume enough energy, disease or parasitism increases w/ density, per capita death rate m increases
- decrease b or increase m results in lower per capita rate of increase r.
logistic population growth model
- per capita rate of increase declines as carrying capacity reached
- Population growth greatest when population approx half of carrying capacity (many reproducing individuals)
- sigmoid (S-shaped) when N plotted over time
- New individuals added to pop most rapidly at intermediate pop sizes, when not substantial breeding population but lots of available space and other resources
Formula logistic
- exponential growth equation, add expression that reduces per capita rate of increase as N increases.
- N number of additional individuals environment accommodate
- (K − N)/K fraction of K that still available for population growth.
- modify the growth rate of pop as N increases:
dN/dt = rinstN[(K − N)/K]
- N small compared to K, (K − N)/K large and per capita rate of increase close to intrinsic rate of increase.
- N is large and resources limit, N approaches K. (K − N)/K small and rate of population growth.
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