WLM Lec 10: Intro to Wildlife Pop. Dynamics

what is usually the focus of wildlife management?

populations

biologist regular monitor...

the habitat conditions in which populations exist

population ecology

an attempt to explain phenomena, such as population cycles, and the underlying causes for the regulation of animal numbers

population

group of organisms, usually the same species, occupying a defined area during a specific time

desnity

number of individuals per unit area

birth rate

number of births per thousand, hundred, or individual per year

age structure

distribution of numbers of individuals of various ages

sex ratios

proportion of male to female sexes in a population

fecundity

number of eggs per female, or number of sperm per male

fertility

percentage of eggs that are fertile

production

number of offspring produced during a period of time

recruitment

the number of new individuals of breeding age in a population

population patterns

all living organisms need resources to survive, and those resources are not unlimited, so most populations are limited at some point

4 factors of population growth

birth rate, death rate, immigration, emigration

death rate

how many individuals are being removed from a population

immigration

how many individuals join a population

Emmigration

how many individuals leave a population

general growth equation

dN/dT = rN

exponential population growth

a population's growth rate increases over time, in proportion to the size of the population

key to exponential growth

number of organisms added to the population increases as the population gets larger

exponential growth formula

dN/dt = rmaxN

logistic population growth

as populations rise in exponential growth, resources are depleted, resulting in slowed growth

key to logistic growth

infinite resources do not exist in the real world

logistic growth formula

dN/dT = rmax ((K-N)/K) N

positive density-dependent factors influencing population growth

Allee effects; predatory vigilance, looking for food, breeding opportunities, group care of young

negative density-dependent factors influencing population growth

negatively impact populations when more individuals are present; group is more detectable to predators, more competition for food and mating opportunities, easier spread of diseases

density-independent factors

happen to populations regardless of how many individuals are there; stochastic events

stochastic factors

random factors that affect population

demographic stochasticity

Random variations in birth and death rates that occur in a population from year to year

genetic stochasticity

accumulations of mal-adaptive alleles or loss of adaptive alleles

environmental stochasticity

unpredictability of major weather events; droughts, floods, fires, etc.

extrinsic factors

factors that influence individual survival externally to them; like predation

intrinsic

factors that influence individual survival internally; genetic factors like genetic diseases or mal-adapted alleles

deterministic factors

habitat quality, predation, disease, interspecific interactions (competition among populations), anthropogenic effects

Lynx-Hare field study

predator-prey interactions; rise in the lynx populations causes a fall in the hare population. The fall in the hare population causes a fall in the lynx population, and subsequently a rise in the hare population. (cycle continues)

how does existing habitat influence birth and death rate?

rate = births - deaths

how does movement impact populations?

rate = (births - deaths) + (immigration - emmigration)

influences on birth and death rates

1. age of sexual maturity for both sexes

2. length of gestation

3. sex ratio

4. mating system

5. number of females that breed at each age

6. number of young per female at each age

7. influence of nutritional condition on reproduction

primary sex ratio

sex ratio at fertilization (50:50)

secondary sex ratio

the sex ratio at birth or hatching, usually approximates 50:50 but may show the first indication of sex-specific mortality

tertiary sex ratio

sex ratio pre-sexual maturity; more sex specific mortality

quaternary sex ratio

sex ratio of adults; sex ratio of most concern due to being linked with productivity

Mating Systems

- monogamy

- polygamy

- promiscuity

monogamy

one mate at a time

Seasonal monogamy

pair bond is formed for a breeding season

true monogamy

having only one mate for one's entire life

Polygamy

having more than one mate at a time

polyandry

One female, several males.

polygyny

One male, several females.

promiscuity

indiscriminate mating; mainly seen in widespread, solitary species (e.g. rabbits, most large cats)

Age specific birth rates

- age often heavily influences reproductive success

- age-specific birth rate separates birth rate by age class

reproduction in short life history species

as females get older, they give birth to more younger

reproduction in long life history species

females have a prime age for reproduction, which decreases as time goes on

mortality

death rate of a population

additive mortality

mortality that actively reduces population size; often density independent, exerts more influence on smaller populations

compensatory mortality

- focuses on multi-causal reasons for mortality

- Ex: if an organism has a disease but is eaten by a predator, it is likely that the organism still would have died to the disease

- often density dependent

Type I survivorship curve

extremely high survival until the individual reaches old age

Type I species

long life history individuals (ex: elephants, humans, many dinosaurs)

Type II survivorship curve

constant mortality across life

Type II species

short life history species that are small in size (ex: rodents and small birds)

Type III survivorship

low survival in young individuals and then become relatively constant in older individuals

Type III species

species born relatively vulnerable, but have high survival at larger sizes (ex: larger reptiles like sea turtles, crocodilians)

Life tables

systematic means of describing mortality as it affects various age groups in a population

Metapopulations

a group of spatially distinct populations that are connected by occasional movements of individuals between them allowing them to function as one big population

theory of biogeography

a theory that demonstrates the dual importance of habitat size and distance in determining species richness

source populations

Populations that occupy and disperse away from high quality habitat patches

Sink populations

Populations that occupy low quality habitat patches; colonized from source populations

ecological traps

areas of low-quality habitat that reduce survival and reproduction

Connectivity

- keeping metapopulations connected to one another

- overpasses and underpasses

problem with population data

obtaining accurate information about animal numbers and densities is one of the biggest wildlife management hurdles

sampling theory

collected data must represent the population at large

population census

the official count of a population

population estimate

an approximation of the true population size based upon sampling a portion of the population

population index

a quantitative measure of a population that doesn't generate exact numbers, but compares abundance over a given time

sources of data

- collection of fish scales by wildlife officials

- submission of wings or tails from game birds

- banding programs

- Christmas Bird count

- Breeding Bird survey

- check stations for big game hunters

- Migratory Bird Harvest Information Program