Unit 3: Populations (3.1 - 3.4) Population Ecology & Growth

generalist species

Species with a broad ecological niche. They can live in many different places, eat a variety of foods, and tolerate a wide range of environmental conditions. Examples are flies, cockroaches, mice, rats, and human beings. .

specialist species

Species with a narrow ecological niche. They may be able to live in only one type of habitat, tolerate only a narrow range of climatic and other environmental conditions, or use only one type or a few types of food. Example: panda

population density

The number of individuals in an area of a specific size (# of individuals/area unit)

K-selected species (K-strategists)

Species that tend to be large, have few offspring, invest lots of time and energy caring for offspring, take a long time to mature, and have long lifespans. (most mammals)

r-selected species (r-strategists)

Species that tend to be relatively small, have many offspring, invest minimal energy and time caring for offspring, mature early, have short lifespans. (most reptiles, amphibians, and insects)

biotic potential (intrinsic growth rate)

The maximum rate at which a population could increase under ideal conditions (like unlimited food & space)

survivorship curve

Graph showing the number of survivors in different age groups for a particular species.

Type I survivorship curve

most individuals survive infancy, live out their life span, and eventually die of old age (e.g., humans).

Type II survivorship curve

individuals die at a constant rate throughout throughout their lifetime (e.g., birds, rodents).

Type III survivorship curve

most individuals die young, with only a few organisms surviving long enough to reproduce and beyond. (oysters, plankton, insects, lots of plants)

J-shaped curve (exponential growth)

Growth where there is unlimited resources and no competition. Population grows without limit

S-shaped curve (logistic growth)

Growth where there are limited resources and the population eventually reaches a carrying capacity

cohort

A group of individuals of the same age. (ex: males 0-5 years old)

Overshoot

when a population becomes larger than the environment's carrying capacity

die-off/dieback

rapid population decline usually experienced after the overshoot of the carrying capacity

causes of dieback

overshoot, famine, drought, disease

carrying capacity (k)

the limit of how many individuals in a population a given ecosystem can sustain (due to limited resources such as food, shelter, water, etc.)

population growth rate

how fast a specific population grows in a specific period of time (births-deaths/total population size)

density dependent factors

limiting factors of population growth that depends on population size (competition for food, limiting nutrients, water, space, mates, etc.)

density independent factors

events that limit population growth regardless of their size (natural disasters like fires, tornados, floods, etc.)

sex ratio

the ratio of males to females in a population. skewed sex ratios (too many males, not enough females) can slow population growth

population age structure

a description of how many individuals fit into particular age categories in a population. The older a population's age structure is, the lower its growth generally, since individuals are past reproductive age.