BSCI103 - Population Ecology

Population ecology

The study of how and why populations change.

Population

A group of individuals of the same species in the same area.

Population dynamics

How populations change over time.

Density

Number of individuals per unit area (e.g., aphids per leaf, humans per square meter).

Clumped dispersion

The most common dispersal pattern, where organisms occur in 'patches' because resources tend to be clumped.

Uniform dispersion

When dispersal is driven by interactions between individuals (such as competition for resources), leading to even spacing (e.g., plants producing chemicals that kill competitors, territorial animals).

Random dispersion

The presence or absence of an organism is due to random processes and a uniform presence of resources (e.g., many wind

Life tables

Used to keep track of survivorship (the chance of individuals to survive to various ages). This is based on the difference between the number of individuals living and dying within a given age interval.

Type I survivorship curve

Chances of survival are very high until advanced age; the usual curve for organisms with few progeny (like humans or elephants).

Type II survivorship curve

The probability of dying is relatively constant at all ages; seen in some invertebrates, lizards, and rodents.

Type III survivorship curve

The probability of dying is very high at low age, but then it lowers when the individual becomes old; a common pattern seen in invertebrates with extremely large progeny.

Population growth models

Ecologists have developed models to understand and eventually protect or control species, based on how species live and reproduce under different conditions.

Exponential Growth Model

Assumes the species can reproduce with no limitation in their environment (growth under ideal conditions), creating a J

Exponential Growth examples

Seen in bacteria when given endless resources, or in the uncontrolled transmission and growth in cases of infectious diseases (such as outbreaks of COVID

Logistic Growth Models

Species usually experience limitations in their environments, so this model takes into account the effect of limiting factors.

Carrying capacity (K)

The number of individuals of a species that a given place has enough resources to support.

Logistic Growth curve

This model adds onto the Exponential Growth model, but controls for the limiting capacity of the environment, leading to an S

Logistic Growth formula

G = rN * (K

Factors limiting population growth

Density

Population cycling

A common pattern where some populations cycle between booms and busts (e.g., snowshoe hare and lynx), with predators often tracking prey, and prey related to resources like food.

Sustainable resource management

A practical application of population ecology, including fisheries, limiting harvest of fish to certain size classes or seasons.

Integrated pest management

A practical application using a variety of population regulation tactics to reduce pests, such as resistant plants, biological control, insecticides, and crop rotations.

Human population growth trends

The human population is growing but the rate is slowing. The rate grew with better medical care and food access, decreasing early mortality and increasing life expectancy. The rate slows as family size declines, and as women's status and education increase (birth rate declines but survival increases).

Age structure & population momentum

Can be used to predict population momentum, specifically the increased number of women in childbearing age, which can predict population growth in other sections of the population in future years.

Age structure & economic trends

Can reveal economic trends, such as an increase in the elderly population in the US and other countries due to increased longevity, which leads to changes in how social security and other services should function.

Ecological footprint

A measure representing the amount of land required to provide raw materials for one individual (the natural resources needed for sustaining the population).

Ecological footprint (consumption)

The US and Western Europe are the greatest consumers of resources, which is limited by the carrying capacity of our environment. Our societies are consuming more than what environmental resources can support, which can lead to events that will reduce population unless voluntary actions are tak