Ecosystem Interactions

Honors Biology Chapter 14

Where & how organisms liveRange- geographical reach

Habitat- where

Ecological Niche- how

Niche includes food, abiotic conditions, behavior

• Competition results when species, in the same community, overlap in use of resources– Strong selective force– Competitive exclusion

• Banishment/extinction

• Evolution• Niche partitioning

Niche (resource) partitioning

Ecological Equivalents – same niche…different communities

Convergent evolution’s fingerprint

Predation – Another interaction with highly selective outcomes

Symbiosis – a kinder interaction, tho’ not without an evolutionary punch

Mutualism – both benefit

Parasitism – parasite benefits, host harmed

Commensalism – one benefits, the other unaffected

Population Dynamics

• Population: all the individuals of a species that live together in an area

• Demography: the statistical study of populations, make predictions about how a population will change

Population Dynamics

• Three Key Features of Populations

• Size

• Density

• Dispersion

• (spatial distribution)

Three Key Features of Populations

1. Size: number of individuals in an area

Influences on Population SizeSurvivorship Reproductive Strategies

1. R Strategists short life span, small

body, reproduce quickly, many young, little parental care

2. K Strategists long life span, large

body, reproduce slowly, few young, parental care,

Three Key Features of Populations

2. Density: measurement of population

per unit area or unit volume

Formula: Dp= N/S

Pop. Density = # of individuals ÷ unit of space

Human Population Density

Three Key Features of Populations

3. Dispersion: describes their spacing relative to each other

• clumped

• uniform

• random

Clumped for protection, resources,mating or social interaction

Uniform dispersion due to intraspecies competition / territoriality

3. Dispersion: describes their spacing relative to each other

Three Key Features of Populations

Random dispersion implies absence of interaction - rare. Mature communities.

Patterns of Dispersion

Population Growth Patterns• Growth Rate: Birth Rate (natality) -

Death Rate (mortality)

• How many individuals are born vs. how many die

• Birth rate (b) + Immigration rate (i) − death rate (d) = rate of natural increase (r).

• Total Growth must add immigration & subtract emigration statistics

Population Growth Patterns

Exponential – J shaped curve Logistic – S curve

Population Growth PatternsThe “Boom Bust” Curve

World Human Population Growth

Other Factors Affecting Population Growth

• Age Structure

POST-REPRODUCTIVE

REPRODUCTIVEPRE-REPRODUCTIVE

Age Demographics for Three Countries

Immigration and Emigration Can Strongly Effect Population Dynamics

Estimated rates of US population growth with or without immigration.

Immigration & Emigration Influences on Total Rate of Growth

Demographic TransitionThe move from “Developing” to “Developed”

Country

Other Factors Affecting Population Growth

• Carrying Capacity- the maximum population size that can be supported by the available resources

– There can only be as many organisms as the environmental resources can support

Carrying Capacity

Carrying Capacity (k)

Time

J-shaped curve (exponential growth)

S-shaped curve (logistic growth)

#

Other Factors Affecting Population Growth

• Limiting Factors - any biotic or abiotic factor that restricts the existence of organisms in a specific environment.

Two Types of limiting Factors

1. Density-dependent factors- increase effect as population size increases. (disease, competition, parasites)

 4. Density-independent factors- affecting populations regardless of

their density (temperature, storms, habitat destruction, drought)

Gradual, sequential change in an area that regenerates or creates a community an area

Succession at Mt. St. Helens.

Ecological Succession

Succession after the Yellowstone fires.

Primary succession: occurs where life has not previouslyexisted

Retreating Glaciers at Glacier Bay Alaska

Primary Succesion – Very Slow

Secondary Succession – Faster (soil already present)

Mount St. Helens

Succession• Climax Community theoretical end-point of

succession. Stable community.