Chapter 52: Population Ecology

Every Pop contains

geographical range and habitat

why do species large body sizes have lower pop densities than small body size species

each lg organism consumes more available resources than each small one

• pops denser in the center of their ranges

how to count species of small size?

sampling and extrapolation

random dispersion

individuals in a pop were distributed unpredictably

clumped dispersion

individuals grouped together

causes for clumped dispersion

social groups, spotty resources, low dispersal, (cant move fast), mating behavior, predation/defense

uniform dispersion

individuals in a population repel each other bc resources are in short supply

age structure

statistical desc of the relative numbers of inds in each age class

3 categories of age structure

prereproductive, reproductive, postreproductive

generation time

average time btwn birth of rganism and birth of its offspring

sex ratio

num of females in pop bigger impact on pop growth than males

demography

study of processes that change pop size and density over time

use of demography

to predict future pop growth

life table

shows pop demographic characteristics

life table marking cohort

taking group of similar age individuals at birth and monitoring survival til they die

life table age specific mortality

proportion of inds alive at beginning of an age interval that died during

life table age specific fecundity

average number of offspring made by surviving females during each age interval

how is energy stored in the body

as starch, glycogen or fat

3 functions of energy for

maintenance, growth, reproduction

semelparity

give birth once

iteroparity

give birth multiple times in life

disadvantage of early reproduction

early reproducers may be smaller and weaker bc didnt spend energy on growth/maintenance

disadvantage of late reproduction

if delay reproduction, could die before next breeding season

r ?

per capita growth rate

logistic model of exponential growth assumes

population’s per capita growth rate (r ) decreases as population increases

why does pop grow slow when pop size is small and when it is large?

small: few individuals are reproducing

large: per capita population growth rate is low

why does pop growth quickly at intermediate pop sizes?

sizeable num individuals are breeding and per capita pop growth rate is high

intraspecific competition

dependence of two or more inds in a pop on the same resource

limitations of a model depicting intraspecific competition

the assumption survivorship and fecundity respond immediately to changes in pop density

density-dependent

influence increases and decreases with the pop density

effects of crowding

• decreases individual growth rate, adult size, and survival of plants & animals

• less energy for reproduction bc trying to survive

• affects developmental and behavioral changes

intraspecific competition

comp btwn pops of diff species

what are density-dependent factors in regulating pop size?

• Intraspecific competition (resource limitation) is the primary factor

• predation

• disease, including parasitism

Density independent factors examples

fires, earthquakes, climate change

r selected life history

function well in changing environments

• small, short gen times, produce in a single reproductive event, grow exponentially when conditions are favorable

k selected life history

more stable environments

• large, long gen times, produce offspring repeatedly during lifetime

• often affected by density dependent factors

metapopualtion

a group of neighboring pops that exchg individuals

what maintains a metapopulation

disperal and gene flow between local populations

source populations

stable/inc in size—possible source of immigrants to other populations

sink populations

decrease in size—receive available immigrants

population densities in the far north

flucturate between species specific lows and highs in a multi year cycle

intrinsic control

as an animal pop grows inds

• undergo hormonal changes that inc aggression

• reduce reproduction

• foster dispersal

extrinsic control

relationship between a cycling species and its food/predators

3 reasons for humans not being affected by density dependence

1. expanding geographical range to all globe through tech

2. industrialization can sustain necessities to large populations

3. public health advancements

what is ecological footprint

sum total of all resources we use

life history traits

• age maturity

• life span/longevity

• fecundity (num offspring per reproductive episode)

• gestation

• parity (number of episodes per reproduction)

• parental investment

survivorship curve

the probability of surviving changes with age/stage

survivorship curve Type I

human (high prob surviving young low prob surviving old)

survivorship curve Type 2

squirrels (equal prob dying young vs old)

survivorship curve Type 3

sea turtles (prob dying young much higher)

growth rate

number of new individuals born minus the number of individuals dead in a given amount of time.

geometric growth model

• assumes constant ratio per generation (give birth at same time)

  • very unrealistic

  • assumption of unlimited growth

  • stair-step graph

exponential growth model

• assumes unlimited growth

• r = per capita growth rate

  • if r>0, the pop grows, if r<0, the pop declines

  • under ideal conditions, r = r_max = intrinsic rate of increase

    • The shorter the generation time, the higher r_max

logistic growth model

• incorporates resource limitation, most realistic

• produces S-shaped curve

• growth is fastest at N=K/2

• low density = slow growth, high density = limited

• populations fluctuate around K

why K and why R

K selected species are around carrying capacity

R selected species because of r = per capita growth rate

in what context may carrying capacity be overshot and why

in lab cultures

• individuals store internal energy reserves & keep reproducing even as resources decline

• reproduction lags behind limitation creating an overshoot

• followed by a rapid pop decline

density independent factors include and affect what parts of population

• devastating event or temp change, climate change

• affect all members of population, no matter how fit they are

geometric model growth rate

The population increases by a constant proportion over a fixed, discrete time interval, such as an annual breeding season

exponential model growth rate

The population's per capita growth rate is constant, causing the population to grow at an accelerating rate over time

logistic model growth rate

The per capita growth rate decreases as the population size approaches the maximum limit that the environment can sustain

geometric growth timing

Occurs in populations that reproduce in discrete periods, with generations that may not overlap

exponential growth timing

Occurs in populations that reproduce continuously

logistic growth timing

Occurs in populations that reproduce continuously, but whose growth is constrained by environmental limits.

geometric growth environmental factors

Assumes that resources are unlimited and environmental conditions are ideal

exponential growth environmental factors

Assumes unlimited resources and ideal environmental conditions, which does not happen indefinitely in nature

logistic growth environmental factors

Incorporates the concept of carrying capacity (K), the maximum population size an environment can sustainably support

example uses for geometric growth

• Rapid, unchecked increase

• Ideal for seasonal reproduction: This model is useful for describing populations that reproduce at fixed, discrete intervals, like many insects that have one or two breeding seasons per year.

example uses for exponential growth

• Pioneer species: This model can represent the initial population explosion of a pioneer species colonizing a new, uninhabited area with no natural predators or resource limitations.

• Bacterial cultures: Bacteria grown in a lab under ideal conditions with a constant, plentiful supply of nutrients will reproduce continuously, showing a classic J-shaped exponential growth curve.

• Early human population: The early period of human population growth is sometimes described as exponential, as growth accelerated over centuries with increasing advancements in medicine and agriculture. 

example uses for logistic growth

• Natural ecosystems: This model provides a more realistic description of natural populations because it accounts for environmental limitations. A small population may grow exponentially at first, but growth slows as it nears the environment's carrying capacity due to factors like resource scarcity, increased competition, or predation.

• Invasive species: The logistic model can describe how an invasive species population, with an initially rapid growth rate, eventually levels off as it saturates the environment and depletes available resources.