Chapter 14

Interactions in an Ecosystem

Animals and Their Habitats

Biotic vs. Abiotic Factors

• An ecosystem is made of both biotic and abiotic factors.

• What biotic factors might scientists find in a Spectacled Bear’s habitat?

• What abiotic factors might be in a Spectacled Bear’s habitat?

• How do these factors differ for Polar Bears?

Habitat vs. Niche

• Habitat – describes the organism’s environment• Niche – describes how the organism interacts

with its environment– Includes both biological and physical conditions in

which an organism lives and how the organism uses those conditions for survival

– It can include its place in the food web, preferred temperature, and abiotic factors

– It is specific to each organism

Competitive Exclusion Principle

• This fundamental rule of Ecology states that no two species can occupy the same niche in the same habitat at the same time

• Why?

Symbiosis

• Symbiosis – any relationship where two species live in close contact

• Mutualism – both species benefit from the relationship

• Commensalism – one species benefits and the other is neither helped nor harmed

• Parasitism – one species harms the other

Mutualism, Commensalism or Parasitism?

How Populations Grow

• Important characteristics of populations: geographic distribution, density, growth rate

• Population density – number of individuals per unit area

• Population dispersion patterns: clumped, uniform and random

Survivorship Curves

• Survivorship curves are generalized diagrams showing the number of surviving members over time from a measured set of births.

• Type 1 – large mammals, low infant mortality, large number of elderly

• Type 2 – birds, small mammals, reptiles, equal survivorship rate through out ages

• Type 3 – fish, amphibians, plants, high mortality, high birth rates

Population Growth

• Populations fluctuate depending on different ecological pressures: births, deaths, immigration, emigration, etc.

• Immigration – individuals moving into an area• Emigration – individuals moving out of an area

Exponential Growth

• Occurs when the individuals in a population reproduce at a constant rate

• Typically occurs when a population has abundant space and food, and is protected from predators and disease

• Characterized as “unrestricted growth” meaning there are no external pressures placed on the population

• Will cease when carrying capacity is reached

Logistic Growth

• Begins as exponential growth• Population growth slows as a population

reaches its carrying capacity – the largest number of individuals an environment can support

• Birth rate may decline, death rate may increase, immigration or emigration may be fluctuating

Limits to Growth

• Limiting Factor – a factor that causes population growth to decrease

• Examples:

Density-dependent Limiting Factors

• These factors depend on population size• Competition – what happens when the

population increases, but resources stay the same?

• Predation – natural way of controlling population; predator-prey relationship is fluctuating

• Parasitism and Disease – may become more prevalent during high population density; limits population size similarly to predation

Density-independent Factors

• Affects all populations in similar ways, regardless of population size

• Examples:

Ecological Succession

• Ecosystems change in response to human as well as natural disturbances.

• What happens to an area after a forest fire? After a volcanic eruption?

• Primary succession – succession the occurs where no soil exists and usually begins with pioneer species

• Secondary succession – when change to the land occurs without removing the soil

Human Population Growth

• Human populations are affected by the same type of factors as other populations

• Because of technology, we have been able to increase our population size quickly

• Some say we have reached or even exceeded Earth’s carrying-capacity

• At the moment, we are still experiencing exponential growth

• Do you think we will experience logistic growth at some point?

Patterns of Population Growth

• Demography – the study of human populations• Scientists try to predict how human

populations will change over time based on birth rates, death rates and age structures

• Population growth has slowed in the US, Japan and Europe in the last 100 years

• Scientists refer to this as the demographic transition

Age Structure Diagrams

• Can be used to predict future population growth