55 introduction the species that live together in a particular area constitute an ecological...

55 Introduction

• The species that live together in a particular area constitute an ecological community.

• Each species interacts in unique ways with other species in its community and with its physical environment.

• The species that form an ecological community, together with the physical environment, constitute an ecosystem.

55 Quiz

• Explain what species richness is and how it is linked to primary productivity.

55 Communities: Loose Assemblages of Species

• Ecologists ask the following questions:

What patterns exist in ecological communities and ecosystems?

How does the physical environment influence those patterns?

What are the relative roles of historical accident and current interactions?

How does evolution influence the assemblage of species that live together?

55 Process and Patternin Communities and Ecosystems

• Organisms need energy inputs, water, and minerals for metabolism and growth.

• The sun is the source of energy, either directly or indirectly, for almost all organisms.

• About 5% of solar energy is captured by photosynthesis.

What happens to the rest?


• The rate at which plants assimilate energy is called gross primary productivity.

• Some energy is used for their own metabolism; the rest is stored or used for growth or reproduction.

primary production.

• The energy available to organisms that eat plants is called net primary production.

• Gross – Amount used = Net

Figure 55.3 Energy Flow through an Ecosystem


• Where is primary production at it’s maiximum?

Where the conditions allow for growth for extended times.

Tropics -Warm and wet.

• Where is it less? Cooler climates, high altitudes.

Figure 55.4 Primary Production in Different Ecosystems (Part 2)

Figure 55.5 Net Primary Production of Terrestrial Ecosystems


• Organisms in a community can be categorized into trophic levels depending on how they get their food.

Primary producers-Autotrophs/photosynthesizers.

Primary Consumers-Heterotrophs/Eat plants (herbivores)

Secondary Consumers- Eat primary consumers.

Examples??????


• Detritivores or decomposers consume dead organisms.

• Organisms that eat foods from primary producers and another trophic level are omnivores.

• A sequence of linkages in which a plant is eaten by an herbivore, and so on, is called a food chain.

• Food chains are usually interconnected to make a food web, because most species eat or are eaten by more than one species.

Figure 55.7 Food Web of Isle Royale National Park


• Energy pyramids show how energy decreases as it flows from lower to higher trophic levels.

10% rule What happens to the rest?

Lost as heat, waste, etc.

Figure 55.8 Pyramids of Biomass and Energy


• Much of the energy in biomass is consumed by detritivores.

• Detritivores, such as bacteria, fungi, worms, mites, and insects, transform the remains and waste products of organisms into CO2, water, and minerals.

• Continued ecosystem productivity depends on rapid decomposition of detritus.

Recycling of nutrients and energy.


• Species whose influences on ecosystems are greater than would be expected on the basis of their abundance are called keystone species.

• They may influence both the species richness of communities and the flow of energy and materials through ecosystems.

• Beavers, for example, create habitats for other species by cutting down trees and building dams.


• Large grazing mammals, such as bison, change the structure and composition of vegetation.

• Bison prefer grasses to forbs (small broad-leaved plants). When bison are excluded from an area of prairie, grasses dominate the ecosystem. When bison are present, they eat the grasses and make space for forbs.

• Bison urine is broken down quickly, providing nitrogen for plant uptake. Plants in areas grazed by bison have higher leaf nitrogen levels and grow faster.


• Sea star Pisaster ochraceous of the North American Pacific coast.

Eats mussels to make room for other species.

Sea stars removed 28 species of animals and algae

disappeared.

55 Disturbance and Community Structure

• Ecological succession is the sequence of changes in the species composition of a community over time.

• Primary succession begins with the establishment of organisms on newly available sites that previously had no organisms.

• Secondary succession begins when organisms reestablish themselves on disturbed sites where some organisms survived the disturbance.

55 Disturbance and Community Structure

• The changes that take place when all or part of the dead body of an animal or plant is decomposed are examples of secondary succession.

• The needle litter under pine trees is decomposed by a succession of fungal species.

• Each group of fungi gets energy by decomposing certain compounds and converting them to other compounds that are used by the next group of fungal species.

55 introduction the species that live together in a particular area constitute an ecological...

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