Biology 10, Las Positas College
Community Ecology & Biodiversity
Chapter 40

I-Community Ecology

A-Overview
B-Interspecific Interactions
C-Disturbances
D-Human Impact

II-Biodiversity

A. Conservation
B. Humans vs Biodiversity

 

I-Community Ecology

A-Introduction
Population = individuals of the same species.
Community = grouping of populations of different species living together in a particular area at a particular time.

Influenced by habitat which includes physical and chemical conditions, such as topography, soil, weather -> availability of food and other resources -> adaptive traits of species -> interactions among species. Independent factors = arrival and disappearance of species and physical disturbances in habitat.

Habitat = actual area in which organism resides.

Niche = role of organism within an ecosystem. Refers to the organism's use of the biotic and abiotic resources in its environment. = space, food, temperature, appropriate conditions for mating, requirements for moisture.

Community Depends Upon

Diversity – the variety of different species = species richness & the relative abundance of the different species

Prevalent form of vegetation – types & structural feature of plants, -> kinds of animals in community

Stability – community’s ability to resist change & return to its original species composition after being disturbed. Depends on community & on disturbance.

Trophic structure – feeding relationships among species making up the community.

B-Interspecific Interactions

1. Competition - Organisms of different species that live near one another strive to obtain the same limited resources. Can be through behaviors or merely by being there.

Competitive Exclusion – some species are so much more adapted to environment that they entirely eliminate other species.

Ecological Niche – competition often results in niche subdivision, i.e. competitors use slightly different resource.

Resource Partitioning – two species use same resources, but different segment of it.

2. Predation - An organisms of one species kills and eats an organism of another. Includes animals eating animals, animals eating plants and plants eating animals.

Controls numbers
Provides evolutionary pressure
Plants and herbivore are in constant evolution to try to protect themselves and get enough nutrients to survive.

Other factors, such as competition, weather, etc. also influence predator, prey numbers.
Predation can -> species diversity in community. Prevents well-adapted species from becoming dominant and killing everything.

3. Symbiotic Relationships

a. Parasitism - An organism of one species (the parasite) lives in or on another (the host). The parasite benefits from this relationship, whereas the host is usually harmed.

b. mutualism – two species live together in close association, both benefiting from the relationship

C-Disturbances – natural & unnatural that change a biological community.

Succession - the dynamic process of change during which a sequence of communities replaces one another in an orderly and predictable way.

1. Primary succession - takes place in areas not previously supporting organisms. Lakes formed from the retreat of glaciers, or volcanic islands.

Plants and animals form climax community (a community in which the mix of plants and animals becomes stable; the last stage of succession).

2. Secondary succession - in areas that have been disturbed and that were originally occupied by organisms. . Also may take place after natural disasters such as forest fire or a volcanic eruption producing ash.

Cyclic nondirectional changes – repetitive changes in a habitat

Keystone species

Restoration Ecology

D-Human Impact

Land use – farming, logging, grazing etc. -> changed mix of organisms
Introduced species – may be more adapted to environment and kill natives -> change in mix of organisms

II-Biodiversity

A. Conservation

1. Endangered Species

An endangered species has so few individual survivors that the species could soon become extinct over all or most of its natural range.

Causes

1. habitat loss & fragmentation
occurs when a large, continuous area of habitat is reduced in area & divided into two or more isolated areas.

Problems:

1. a decrease in the sustainable population size for many species when an existing population is divided into two or more isolated subpopulations
2. Increased surface area or edge, which makes some species more vulnerable to (1) predators, (2) competition from nonnative & pest species, (3) wind, (4) fire
3. Creation of barriers that limit the ability of some species to (1) disperse & colonize new areas, (2) find enough to eat, (3) find mates.

2. overharvesting

2. Conservation

Sensible & careful use of natural resources by humans.

Process -> conservation & solving environmental problems

1. Identify resources.
2. Identify problems.
3. Look for solutions.
4. Implement solutions.

Bioeconomic Analysis

Lists costs & benefits of activity to economy & environment.
Most things cost more than we think because we do not include environmental cost.

Methods of discouraging environmental degradation:

1. phase in government subsidies & tax breaks that encourage environmentally beneficial behavior
2. phase out government subsidies & tax breaks that encourage environmentally harmful behavior
Ex: cattle grazing on public land

Paul Hawken’s motto for an environmentally sustainable economy: "Leave the world better than you found it, take no more than you need, try not to harm life or the environment, and make amends if you do."

B. Humans vs Biodiversity

People will only conserve if they can see benefits.

2 success stories

1. Strip logging

2. Ranching & Riparian Zones