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 Niche 1. 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