11/7 Population Ecology 3

Demography

the tracking of vital statistics of a population over time (birth rates, death rates, immigration rates, and survival to reproduction)

What is a life table?

An age-specific summary of the survival pattern of a population

Why is a life table useful?

It's useful for understanding population dynamics, predicting growth/decline, identifying high-risk life stages (like infancy or old age). 

Survivorship Curve

a graphic way of representing the data in a life table

Survivorship

how many of the original group has made it to the next class

What are the three kinds of survivorship curves?

Type I, Type II, Type III

Type I

Young-Middle Age = high survivorship, Old = low survivorship

Type II

steady survivorship

Type III

Young = low survivorship, Adult-Old = high survivorship

What are life history trade-offs?

When organisms must split energy across survival, reproduction, and growth

Example 1 of Life History Trade-Offs

Produce a moderate number of large seeds that provide a large store of energy. Most survive.

Produce a large number of small seeds. At least some of them will survive.

Example 2 of Life History Trade-Offs - Frequency of Reproduction

Semelparity and Iteroparity

Semelparity

reproduce once, high number of offspring 

Iteroparity

repeated reproduction after a certain age, lower number of offspring

Examples of life history traits

mating strategy, birthing interval, gestation time, parental investment (reproduction); size at birth, size at sexual maturity, max size, rates/patterns of growth (growth); longevity, predation, seasonal environments, feeding ecology (survival)

Why does the environment have an effect on life history traits?

Because species must adapt to the conditions of the environment.

How do environmental stability and predictability differ?

Environmental stability refers to the lack of change in an environment over time, while environmental predictability refers to the extent to which future conditions can be foreseen, regardless of whether the environment is changing or not.

What are r vs K selected species?

• r-selected: prioritize high reproductive rates (high r); unstable and unpredictable environments

• K-selected: often quality > quantity because near carrying capacity (K); because density may matter a lot, offspring need best chance of survival; mostly stable and predictable environments

What is bet hedging? 

• Making a variety of offspring types to try to maximize the number that survive

• A strategy for highly variable environments (unstable and unpredictable)