Wildlife Management Exam 3 - Population Dynamics

Why is it necessary for wildlife biologists to understand population dynamics for effective management?

• identify when issues (population declines) occur so adaptive management can happen

• Identify when success (population increase) occurs to justify management practices

• Ensure long term viability of wildlife populations

Define population.

group of individuals of the same species in an area where they can interact (birth/death rates, abundances, and age structures are relevant)

Define population growth rate, open population, closed population

how number of individuals in population changes (increase/decrease/no change) through time

• open population: ones where immigration/emegration occurs (what actually happens in life)

• closed population: immigration/emigration does not occur (theoretical, only happens when species are in an area that they cannot navigate across/disperse)

  • used only to estimate populations within a certain time frame (breeding season)

Define carrying capacity.

maximum population size that can be sustained in an area

Define negative feedback.

increase/decrease in one factor causes corresponding decrease/increase in another (stabilizing)

• fluctuations in carrying capacity (drop in one causes increase in another to keep carrying capacity stable)

Draw a logistic population growth curve

Define limiting factors. Why do you need to identify them?

environmental variables limiting population growth

Ex. food, cover, water, space

• need to identify them as otherwise you are putting resources/$$ into a target species, but you will not get the tarted effect of growing the population due to the limiting factors.

Why would high/low oscillations in negative feedback be problematic?

Species could easily go extinct if something were to happen

• weather can strongly impact: especially ground nesting birds like turkeys

What are population dynamics driven by?

BIDE parameters:

• Births (+)

  • recruitment: number of new juveniles added to the population (as not all born will survive, this is more accurate)

• Immigration (+)

  • enter population

• Deaths (-)

  • survival rate: 1- mortality rate

• Emigration (-)

  • leave population

*Immigration and emigration are dictated by dispersal (permanent movement from one population to another)

What is the equation to calculate future population size?

N_t+1 = N_t + B + I – D – E

N_{t+1 future population size}

N_{t population size at that time}

_{**Note that if your population census was done every 10 years than your future calculations will be based on 10 year intervals.}

What is age structure?

proportion of individuals of certain ages in a population

• Ex. 30% 1 yr olds, 40% 2 yr olds, 10% 4 yr olds

• Higher survival for adults than fawns

What facilitates estimation of abundance and density?

vital rates

Define abundance and density.

Abundance: number of individuals in a population

Density: abundance per unit area

• gives us a standard comparison to make (ex. between years, different sites) (allows you to scale observation to a common amount of space)

What is the equation for population growth rate?

population growth rate = changes in abundance or density through time

What is the geometric growth rate or discrete growth rate? What about the exponential growth rate or instantaneous per capita growth rate?

Geometric growth rate/discrete growth rate

λ = N_t+1 / N_t where t = time (e.g., a given year)

Exponential growth rate/instantaneous per capital growth rate

λ = e^r where e = 2.718 or r = ln(λ) where ln = natural logarithm

• this is key to understanding population dynamics (J shaped curve)

Lamda vs r

Lambda:

• easier to understand

• good when communicating with mangers/general public

• discrete time steps not realistic (populations change in a continuous basis, not these descrete steps)

• <1 decrease, >1 population increase

r

• less intuitive by easier to work with mathematically

• easy to compare among species

• can be averaged across time intervals

• negative = decline, positie = increase

• good when communicating with researchers/biologists. preferred for population ecologist

Is population growth ever exponential?

No! Except for human population (technology, modern medicine) and some types of bacteria

What is the importance of variation/uncertainty in population dynamics?

• process variation: variability in population processes (birth rate, etc.) resulting from nature/management

  • Two types: natural variation (uncontrollable random events -weather), deterministic factors (associate with management activities to increase/decrease population - ex. trapping predators to increase waterfowl chick survival)

• Sample variation/observation error

  • secretive wildlife, imperfect detection

Equation for projecting population change for single or multiple steps

Single steps:

N_t+1 = N_t λ or N_t+1 = N_t (e^r)

Multiple steps:

N_T = N₀ (λ^T) or N_T = N₀ (e^r*T) where N₀ = starting abundance and T = number of time steps

What are factors that affect population dynamics which slow/reduce growth

• stochastic/random factors: genetics, envirometnal

• deterministic factors: habitat, predation, disease

• Density dependance: positive or negative (too many inviduals, browse line, etc.)

**these 3 factors create environmental resistance