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