1. Interactions in an Ecosystem
Chapter 14
Interactions in an Ecosystem

2. Animals and Their Habitats

3. 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?

4. 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

5. 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?

6. 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

7. Mutualism, Commensalism or Parasitism?

8. 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

9. 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

10. 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

11. 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

13. 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

16. Limits to Growth
Limiting Factor – a factor that causes population growth to decrease
Examples:

17. 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

18. Density-independent Factors
Affects all populations in similar ways, regardless of population size
Examples:

19. 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

20. 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?

22. 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

23. Age Structure Diagrams
Can be used to predict future population growth