2. Density-dependence and its consequences in wildlife population dynamics and management

Question 1

Density/population dynamics

Answer 1

Density = abundance / unit area

Population dynamics –> changes in wildlife population over time (not static)

Density dependence process occurs when population growth rates are regulated by the density of a population

Population changes due to
birth < death
Immigration < Emigration

If the death rate increases or the birth rate decreases as a consequence of population density increase, we define these changes as being density dependent ,

Question 2

Growth models

Answer 2

Exponential growth model (Unlimited) - constant rate of increase determined by the given environmental resources

Logistic growth model (limited) - Growing number of animals exhausts resources, leading to increased competition, declining resources per capita, faster spread of disease and parasites
-Stars with exponential phase of rapid growth rate
- Transition phase: Slow, yet high growth rate vs time
- Plateau phase: population remains stable over time, slight oscillations in numbers

Question 3

Carrying capacity (K)

Answer 3

Environmental resistance limits the population growth and determines the carrying capacity of the habitat

K: max population size that can be sustained in that specific environment, given food, habitat, water, and other resources available.

K can be affected by:
-Food shortage or prey
-Predation/ parasitism
-Disease
- Accumulation of waste
- Shortage of space of territory

Question 4

Density dependence effects

Answer 4

Density dependence is stronger at higher densities. Growth is unaffected at low densities, but depressed at high densities. In many cases this leads to regulation of population around the maximum density (K).

Other negative density dependent phenomena are infectious diseases and parasitism, which may cause outbreak at high host population densities

Positive:
-Many annual herding

Negative:
-Influence weaker indiv (young/ old),
-conflicts for food, territory, and reproduction opportunities
- Slower development, less weight gain, and smaller average reproduction

Question 5

Limitation and limiting factors

Answer 5

Limitation:
-Affect morality
Affect birth rate

Limiting factors:
-determine equilibrium population size limitation

**Regulation:
- Regulation is the effect of density dependent factors after disturbance
- Population is always disturbed and never reach equilibrium

**Types of competition
- Exploitation competition: Species compete indirectly through their mutual effects on the available shared resources
-Interference competition: Species compete directly for access to a resource
-Allelopathy: A form of interference competition in which indiv of one species release toxins that harm other species

**Competition in general features
- Effects of competition are unequal or asymmetrical
- Competition will reduce the amount available to each species
- Competing species are more likely to coexist when they use resources in different ways

Question 6

Application of management

Answer 6

-Population control in higher densities
-Ungulates can cause a lot of damage to the environment
-Too high # of predators can decimate prey populations

Examples:
*Red deer on Island of Rum
-No predators
-populations increasing
- When populations reached K:
=Drop in reproduction
=Bad antler and later casting
= lower proportion of animals changing to winter coat