1. Population and Community Ecology
Chapter 35

2. Population Density
Ecologists often describe a population in terms of its density.
Population density is the number of individuals of a particular species per unit area or volume.

3. exponential growth
the population multiplies by a constant factor at constant time intervals.

4. Carrying Capacity
In nature, a population may start growing exponentially, but eventually one or more environmental factors will limit its growth.
The population then stops growing or may even begin to decrease. Space is one example of a limiting factor, a condition that can restrict a population's growth.
Other limiting factors include disease and availability of food.

5. Carrying Capacity
When such environmental factors limit a population's growth rate, the population is said to have reached its carrying capacity.
The carrying capacity is the number of organisms in a population that the environment can maintain
As a growing population approaches carrying capacity, the birth rate may decrease or the death rate may increase (or both), until they are about equal.

6. Competition
This competition within a single species limits the growth of the population.
Within a community, interspecific competition (competition between species) takes place when two or more species rely on the same limited resource.

7. Niches
Within a community, each species has a unique living arrangement called its niche.
A niche includes an organism's living place (habitat), its food sources, the time of day it is most active, and many other factors specific to that organism's way of life.
The local loss of a species due to competitive exclusion is most likely to occur if two species have niches that are very similar.

8. predation an interaction in which one organism eats another.
Predators – animals that hunt and eat other animals.
Prey- animals that get eaten by the predator.

9. Symbiotic Relationships
A symbiotic relationship is a close interaction between species in which one of the species lives in or on the other.
There are three main types of symbiotic relationships: parasitism, mutualism, and commensalism.

10. Parasitism is a relationship in which one organism, the parasite, obtains its food at the expense of another organism, the host.
Examples include blood-sucking mosquitoes, tapeworms that live and feed in the intestines, wasps laying eggs on caterpillar

11. In mutualism, both organisms benefit from the symbiotic relationship.
Clownfish and sea anemones present an example of facultative mutualism. The clownfish benefits by having a protected home territory.

12. Commensalism
is a relationship in which one organism benefits, while the other organism is neither harmed nor helped significantly.
This shows the symbiotic relationship commensalism, the bird gets food from the back of the cow but the cow is not affected

13. Ecological Succession
Communities may change drastically as a result of a disturbance.
A variety of species may colonize the disturbed area.
These species may be replaced as yet other species move into the area later.
This process of community change is called ecological succession.

14. Primary Succession
When a community arises in a lifeless area that has no soil, the change is called primary succession.
Examples of such areas are new islands created by erupting volcanoes, or the bare rock left behind a retreating glacier.

15. Primary Succession
Autotrophic microorganisms are first organisms to appear.
Then lichens and mosses.
Soil develops gradually from the action of these early colonizers and from their decomposed remains.
Once soil is present, grasses, shrubs, and trees grow.
Primary succession from barren ground to a community such as a deciduous forest can take hundreds or even thousands of years.

16. Secondary Succession
When a disturbance damages an existing community but leaves the soil intact, the change that follows is called secondary succession.
An example is a forested area that has been cleared for farming.
Grasses may grow from seeds carried by animals or the wind.
They may be replaced by shrubs, and eventually by trees similar to those in the original forest.