BIOS 230Properties of Populations

Lecture #21

Ecology

• Ecology is the scientific study of the distribution and abundance of organisms and the interactions that determine distribution and abundance.

Evolution provides the mechanism (natural selection) that explains why and how adaptation occurs

Ecology demonstrates how adaptations that arose by natural selection explain the distribution and abundance of organisms

Ecology and Evolution are Closely Connected

• The interactions that determine an organism's distribution and abundance include energy flow, growth, reproduction, predation, competition and many others.

• Biotic: living interactions• Abiotic: nonliving (physical and chemical) interactions

Ecology

Introduction to Ecology

• Biotic components:– Spruce trees, mosses,

understory layer, bacteria & fungi, bald eagle

• Abiotic components:– Sunlight, Nutrients, Water

• Ecosystems include many complex interactions

Spruce forest in coastal SE Alaska

The Hierarchy of Ecological Systems

Individual

Population

Community

Ecosystem

Landscape

Biome

Biosphere

Individual

Ramets and Genets

Is an individual a rametor a genet? Is the population size the number of ramets or genets?

Individual

Population

Community

Ecosystem

Landscape

Biome

Biosphere

A group of individuals of the same species that occupy a given area

Populations of different species interacting within an ecosystem

Incorporates biotic and abiotic components

An area of land or water composed of a patchwork of communities and ecosystems

A geographic region with similar geological and climatic conditions

The thin layer surrounding the Earth that supports all of life

Populations

• A population is a group of individuals of the same species that inhabit a given area– There is a potential for interbreeding among members of the

population (focus of Evolution)– Populations have sizes and spatial distributions that can be

characterized in different ways (focus of Ecology)

Populations

• Key characteristics:– Abundance– Density– Dispersion– Proportion of individuals of

various ages and stages– Birth, death, and movement of

individuals Monarch Butterfly Danaus plexippus

Population Distributions

• The distribution of a species or population describes its spatial location– Influenced by the occurrence of suitable environmental conditions– Influenced by interactions with other species– Different ways to describe distribution

• The broadest description of distribution is geographic range. Geographic range is the area that encompasses all individuals of a species

Geographic Range of the Whale Shark

Geographic range provides only limited information about distributions, at the broadest geographical scale.

Geographic Range of Orangutan

• Historical distribution throughout Southeast Asia, southern China and on the island of Java.

• Current distribution only on islands of Borneo and Sumatra

• Tropical rainforests at altitudes of less than 3,281 feet above sea level.

• Native to North and South America

• No longer in South America

• Introduced (1800s) to Hawaii, South Pacific, Australia

Introduced

Population Distributions

• Individuals are not distributed evenly throughout their geographic range

• Individuals can only occupy areas that can meet their requirements

• Many factors influence distributions within the geographic range

Population Distributions• Crude density is simply the

number of individuals per unit area

• But population density can vary from location to location

Density = 5 individuals/m2 Density =

2 individuals/m2

Density = 0 individuals/m2

A hypothetical population with uneven distribution

Abundance = total number of individuals

(red dots)

Population Distributions

• Dispersion refers to the evenness of the population's distribution through space. There are three population disperson patterns– Random—an individual’s position is independent of others– Uniform—results from negative interaction among individuals– Aggregated (or clumped)—results from patchy resources, social groupings

Uniformly distributed shrubs in the Kara Kum desert of central Asia

Population Distributions

• Spatial distributions may vary at different spatial scales– The shrub Euclea in the savanna ecosystems of Southern Africa

are clumped under Acacia trees, – The Acacia trees are uniformly spaced– Spatial pattern of Euclea is aggregated at one scale and uniform

at another scale

Spatial distribution of Euclea divinorum in African savannas. Individuals are aggregated under the canopy of Acacia trees, which are uniformly distributed themselves.

Population Abundance

• Abundance is the number of individuals in the population and defines its size

• Abundance is a function of:– Population density, or the number of individuals per unit area– The area over which the population is distributed

Estimating Abundance

• Abundance can rarely be directly measured

• In most cases, abundance must be estimated by sampling a portion of the population

• Sampling methods for plants and sessile animals– Counting the organisms in a subsample (quadrats)– Abundance estimates may be skewed by a clumped spatial

distribution

Estimating Abundance - Plants

Abundance estimates may be skewed by an aggregated (clumped) spatial distribution

Estimating Abundance for Mobile Animals: Mark-Recapture Method

• Want to know N, total population size

• Capture animals and mark them, release back to population

• Wait, let animals re-assimilate into population

• Now capture new sample and count the number marked

• Assume that the ratio of marked to sampled individuals in second sample represents the ratio for entire population

• Capture 100 robins, mark and release all, wait• Capture new sample of 50 birds; 10 are marked• Marked ratio is 10/50• In whole population we marked 100 out of N, or 100/N• So 10/50 = 100/N• N=500

Mark-recapture study of squirrels on UIC campusWe trap 10 squirrels, put tags in their ears, and release them back on campus. One month later, we capture 20 squirrels, and 4 have tagged ears. What is your estimate of the population of squirrels on campus?

A. 20B. 40C. 50D. 80E. 200

10/N = 4/20

N = (10 X 20)/4

N = 50