Ecosystems and Living Organisms

Chapter 4

Communities Different populations of organisms that

live and interact together in the same place at the same time Vary in size No true boundaries

Example Rotting Log Organisms in Communities and

Populations compete for resources

Ecosystem The sum of a community and the abiotic

environment. i.e many populations + soil, water,

weather, terrain, etc.

Succession: How Communities Change The stages of community development Colonization and replacement Change in species diversity and abundance Leads to climax vegetation and stability??

Primary Succession Pioneer Community New soil/uninhabited environment Lichens = break down rocks into soil Then mosses, ferns, grasses, shrubs, trees

Secondary Succession After major disturbance where plants once

were Light seeded plants; shade intolerant;

small, fast growing, highly reproductive plants and animals

Animals undergo succession with plant communities

Keystone Species A species in an ecosystem that affects

many other species so that it cannot be readily lost or replaced. Usually affect some type of resource Do not have to be high in numbers Example: gopher tortoise/wolves/panthers

Interactions among organisms Symbiosis

Result of coevolution Types of symbiotic relationships

Mutualism Lichen (algae and fungus)

Commensalism Gray whale and barnacle

Parasitism Mosquito and human Pathogen = causes death and/or disease

Interactions among organisms Predation

Predator (larger, more complex) Prey (might be plants)

Result of Coevolution Selective forces Results of random mutations

Methods of predation Pursuit Ambush

Methods of protection for prey Plant defenses

Spines, thorns, etc. Excretions Toxins Allelopathy (black walnut & cherrybark oak)

Animal defenses Fight or flight Warning coloration Camoflague Poison glands Shells, herds, etc.

Competition Use of common essential & limited resource Intraspecific competition –within a

population Interspecific competition – between

populations Sometimes subtle and complex Organisms that compete may also benefit

each other

The Ecological Niche1. Producer, Consumer or Decomposer?

2. Predator and/or prey?

3. Symbiotic relationships?

Ecological niche – Role in the ecosystem and in habitat

Niches Fundamental niche –

Potential idealized niche

Realized niche – Niche that an organism actually uses

This difference is due to competition

Limiting Factors Any resource that restricts the ecological

niche of an organism Usually simple

Minerals Salt concentration in water Amount of precipitation Temperature Graph p. 77

Competitive Exclusion One species is excluded from part of a

niche because of competition with another species (interspecific competition).

No two organisms can occupy the same niche

Coexistence is possible if niches are reduced

Gause study

Resource partitioning Reduction in competition for resources that

occurs as a result of each species’ niche differing from the others in one or more ways

Species Diversity The number of species present in a community High diversity: tropical rain forests

Low diversity: isolated islands, mountaintops

1. Abundance of potential ecological niches The greater the complexity of the

community, the more potential niches available

More niches available, the more organisms The more organisms, the more diversity

2. Location at the margins of adjacent communities Species diversity is greater at the margins

of adjacent communities Ecotone – A transitional zone where two

or more communities meet Edge effect - The change in species

composition at ecotones

3. Geographical isolation The more isolated the community, the less

diverse it will be Cannot be readily replaced Contain fewer potential niches Island biogeography

4. Dominance of one species over another When one species uses more than its share

of resources It out competes other species Kangaroo rats

5. Environmental Stress The more environmental stress, the less the

species diversity Polluted stream vs. clear stream Urban vs. rural areas Temperature

6. Geological history The older the community, the higher the

species diversity Glaciers Volcanoes Islands Continental Drift

Ecosystem Services Provided by the ecosystem

Clean air, water Fertile soil

The more diverse an area, the better the ecosystem services

Community Stability The ability of a community to withstand

environmental stresses and disturbances The greater the species diversity, the more

stable the community and the less important the species American Chestnut