Ecology and Evolution exam 3

Life History Traits

timing, amount of resources allocated to growth, maintenance, and reproduction

Life History Strategy

Specific ways organisms manage growth, maintenance, and reproduction to maximize lifetime reproductive success (fitness)

What are the three main functions energy can be allocated to for the optimal life strategy?

Growth, Maintenance(survival), Reproduction

What are Optimal Life History Strategies constrained by?

Trade-offs

Life History trade-off

Allocating more energy to one function means there is less energy to allocate to a different function

Semalparous

Annual plants, produce once in a lifetime then die

Iteroparous

Perennial plants, produce many times in a lifetime

Where do semelparous plants allocate most of their energy?

Reproduction

Where do iteroparous plants allocate most of their energy?

Maintenance (survival)

Senescence

The deterioration of biological function with age

Mutation accumulation hypothesis for senescence

Alleles that cause late-onset disease maintained at higher frequency than alleles causing early-onset disease

Antagonistic pleiotropy hypothesis for senescence

Mutations that cause benefit earlier in life will spread, even if it causes disease later in life

Menopause

The end of a females fertility but survivorship continues on

What other animals besides humans go through menopause (have a post-reproductive life span)?

whales

Fecundity

People have more kids when post-reproductive mother is alive

Lifetime reproductive success (number of kids raised to reproductive age)

People successfully raise more kids when post-reproductive mother is alive

Grandmother hypothesis

Selection favors menopause because females that live beyond their reproductive lifespan have more surviving grandchildren (because they help their own children have more children)

Why do women go through menopause?

The cost of menopause is offset by the benefits of the increased number and survival of grandchildren

Population growth models

Using mathematical equations to project future populations growth/decline

Annual population growth rate

N(t+1) / N(t)

t=time

N =population size at time called lambda (λ)

t in subscript

λ>1

population is growing

Log scale

Each interval = equal ratio of change (x10)

Linear scale

Each interval = equal amount of change

When population growth rate is constant

straight line on a log scale (because population growth is multiplicative)

Linear scale is good for...

Showing raw amount of change across time

Log scale is good for...

showing rate of change across time

What kind of growth occurs when lambda is constant?

Geometric population growth

Geometric population growth equations

N(t+1) =λN(t)

N(t)=N(0) x λ^t

t in subscript

When is lambda good/not good

Good: measuring actual population growth from censuses at discrete time periods

Not good: mathematical models to explore different population dynamics

How do you find the rate of change at a single point in time?

Tangent line. (dN/dt)

Exponential population growth

same as geometric population growth, but for case where reproduction occurs continuously

Exponential population growth equations

dN/dt = rN

r=exponential growth rate

Nt = N0 x e^rt

t and 0 in subscript

λ=e^r

r

per capita growth rate that a population is capable of.

Per capita growth rate of a population

the rate of growth per individual (1/N x dN/dt)=r

Population regulation

The limit to population growth

Density independent factors that limit population growth

Effects on birth and death rates unrelated to the number of individuals in the population

Density dependent factors that limit population growth

Factors that affect birth and death rates differently as population size changes

Logistic population growth

Population increases rapidly, then stabilizes at the carrying capacity(k).

K

maximum population size that can be supported indefinitely by the environment

Logistic population growth model

models density dependent population growth

Logistic growth equation

dN/dt = rN(1 - N/k)

In logistic growth when N«k

population grows almost like exponential growth

In logistic growth when N is close to k

population stops growing

Carrying capacity

when birth rate = death rate

when dN/dt = 0

per capita growth rate is 0

Maximum sustainable yield

real-world application of the logistic growth model

What is a use of maximum sustainable yield

harvesting goal of fisheries

Why is human population growth rate declining even though death rate is declining

birth rate is declining

Demographic transition

birth rate decline happens after death rate declines

General demographic rule in humans

1) initial, stable population

2) death rate decline, causing population to grow

3) birth rate declines

4) Birth rate = death rate again

Extinction vortex

once a population starts to decline, at a certain point they can get into a spiral they can't get out of

Causes of extinction vortex (population decline)

Inbreeding depression: increases expression of deleterious traits

Variability (stochasticity) of population growth rate: increases chance of extinction (environmental and demographic)

Allee effects: can cause further decline due to positive density dependence

Inbreeding depression

A small population size increases the probability of two deleterious recessive mutations coming together in homozygous state

Genetic rescue

counteracting inbreeding depression with gene flow

Environmental stochasticity

environment can fluctuate randomly, causing variability in population growth

Examples of environmental stochasticity

changes in food abundance, changes in water availability, and changes in temperature

Demographic stochasticity

random chance can also cause variation in death and birth rates

why does population size fluctuate a lot

demographic stochasticity

Demographic stochasticity can cause populations to shrink even when

mean population growth rate is stable (or even positive) which is dangerous for small populations

Allee effects

growth rate can decrease as population density decreases

Potential causes of allee effects

1) animals that live in groups lose benefits of grouping

2) When populations get super small, individuals can't find mates

3) When a species becomes rare, other species that it interacts with go away

Population viability analysis

predicting extinction risk given various causes of populations fluctuations