1. Chapter 4 Section 2 What Shapes an Ecosystem?
Objectives:
Explain how biotic and abiotic factors influence an ecosystem
Identify the interactions that occur within ecosystems
Describe how ecosystems recover from a disturbance

2. Biotic and Abiotic Factors
Ecosystems are influenced by a combination of biological and physical factors.
The biological influences on organisms within an ecosystem are called biotic factors.
Includes the entire cast of characters with which an organism might interact.
For example: birds, trees, etc.

3. Biotic and Abiotic Factors
Physical, or nonliving, factors that shape ecosystems are called abiotic factors.
For example: temperature, precipitation, humidity, wind, nutrient availability, soil type, sunlight, etc.

4. Biotic and Abiotic Factors
Together, biotic and abiotic factors determine the survival and growth of an organism and the productivity of the ecosystem in which the organism lives. (KEY CONCEPT)

5. The Niche
A niche is the full range of physical and biological conditions in which an organism lives and the way in which the organism uses those conditions. (Its job)
The combination of biotic and abiotic factors in an ecosystem often determine the number of different niches in that ecosystem.

6. The Niche A niche includes: an organism's place in the food web
range in temperatures that an organism needs to survive
type of food an organism eats
how it obtains this food
which other species use the organism as food
when and how an organism reproduces

7. Community Interactions
Community interactions, such as competition, predation, and various forms of symbiosis, can powerfully affect an ecosystem. (KEY CONCEPT)
Symbiosis = interaction between two different organisms living in close physical association, typically to the advantage of both

8. Community Interactions
Competition
Occurs when organisms of the same or different species attempt to use an ecological resource in the same place at the same time.
Resource: any necessity of life (i.e. water, nutrients, light, food, or space)

9. Community Interactions
Competition (continued)
Direct competition in nature often result in a winner and a loser - with the losing organism failing to survive.
competitive exclusion principle: no two species can occupy the same niche in the same habitat at the same time.

10. Community Interactions
Predation
predation: an interaction in which one organism captures and feeds on another organism
predator = the organism that does the killing and eating

11. Community Interactions
Symbiosis
symbiosis “living together”: any relationship in which two species live closely together
3 classes of symbiotic relationships:
mutualism
commensalism
parasitism

12. Community Interactions
mutualism: both species benefit from the relationship
commensalism: one member of the association benefits and the other is neither helped nor harmed
parasitism: one organism lives on or inside another organism and harms it.
The parasite obtains all or part of its nutritional needs from the other organism
mutualism = insects pollinate flowers, flowers give them food
commensalism = barnacles on a whale
parasitism = a tick

13. Ecological Succession
Ecosystems are constantly changing in response to natural and human disturbances. As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community. (KEY CONCEPT)
ecological succession: The series of predictable changes that occurs in a community over time

14. Ecological Succession
Primary Succession
primary succession: succession that occurs on surfaces where no soil exists.
pioneer species: the first species to populate the area

15. A volcanic eruption destroys the previous ecosystem
The first organisms to appear are lichens
Mosses soon appear, and grasses take root in the thin layer of soil
Eventually, tree seedlings and shrubs sprout among the plant community

16. Ecological Succession
Secondary Succession
Components of an ecosystem can be changed by natural event, such as fires, or by human activities, such as farming.
secondary succession: occurs when a disturbance of some kind changes an existing community without removing the soil

17. 4-2 Section Assessment
What is the difference between biotic factor and an abiotic factor?
Name three types of community interactions that can affect an ecosystem.
What is the difference between primary succession and secondary succession?
How is an organism’s niche determined?