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Interactions in an Ecosystem
Chapter 14 Interactions in an Ecosystem
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Animals and Their Habitats
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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?
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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
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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?
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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
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Mutualism, Commensalism or Parasitism?
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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
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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
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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
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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
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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
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Limits to Growth Limiting Factor – a factor that causes population growth to decrease Examples:
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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
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Density-independent Factors
Affects all populations in similar ways, regardless of population size Examples:
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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
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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?
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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
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Age Structure Diagrams
Can be used to predict future population growth
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