9 – Population Dynamics

4 Determinants of population size

Birth, Death, Immigration, and Emigration.

Population dynamics

Changes in population size and their implications for extinction, conservation, and resource management.

What is the "numerical response" in dispersal?

A change in predator numbers in response to prey density.

3 Drivers of dispersal

Climate change, food availability, and transport (e.g., water currents).

Dispersal in flowing systems

Colonization and upstream movement counter downstream drift to maintain populations.

Subpopulation

A part of a larger population sustained via immigration.

Metapopulation

A group of subpopulations that are all connected. Key determinant of local population size in metapopulations;Isolation by distance.

Factors that increase population size

Births and Immigration.

Factors that decrease population size

Deaths and Emigration.

Type I Survivorship Pattern

High survival among young; common in large vertebrates, some plants, and protists.

Type II Survivorship Pattern

Constant survival rates regardless of age; common in birds and turtles.

Type III Survivorship Pattern

High mortality among young; common in fish, marine invertebrates, and some plants.

Age distribution

The proportion of individuals of different ages within a population.

What can age distribution reveal?

Temporal climate variation and the effects of environmental conditions on demographics.

Example: Drought impact on age distribution

A 1977 drought's effect on high mortality can remain visible in population data 10 years later.

Definition: Life table

A list of survivorship and mortality (deaths) within a population.

Cohort life table

Follows a specific group from birth to death; easy to interpret but hard to collect.

Static life table

Records the age at death for many individuals; requires age estimation.

4 Metrics provided by life tables and fecundity schedules

Net reproductive rate ($R_0$), Geometric rate of increase ($\lambda$), Generation time ($T$), and Per capita rate of increase ($r$).

Ecological uses of life tables

Estimating survival, predicting population declines, and managing endangered species.

Societal uses of life tables

US SSA budgeting for mortality and translational geroscience to maximize human lifespan.