Transcript Essentials of Biology Sylvia S. Mader

Essentials of Biology
Sylvia S. Mader
Chapter 31
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
31.1 Ecology of Communities
• A community is a collection of different
species of living organisms.
• In some communities, some populations
affect the evolution of other populations
(coevolution).
• An ecosystem consists of a community
and the physical environment.
Community Composition and
Diversity
• Two characteristics can be used to
describe a community.
– Species richness includes the variety of
different plant species in a community.
– Diversity includes the richness and relative
abundance of individuals of different species.
Ecological Succession
• As communities change over time, they
typically go through an ordered process of
change called ecological succession.
• The climax-pattern model of succession
maintains that the climate of an area leads
to the same stable climax community.
Two Types of Succession
• There are two types of succession.
– Primary succession occurs where soil has not
formed.
– Secondary succession occurs on a disturbed
site with soil (such as an old agricultural field)
that returns to a natural pattern of community
change.
Two Types of Succession (cont.)
Interactions in Communities
• The species in a community can interact in a
variety of ways.
– Competition occurs when species compete for the
same resource.
– In predation, one species preys upon another.
– In parasitism, one species is a parasite on another.
– In commensalism, one in which the interaction
benefits one species, but the other is not affected.
– In mutualism, the interaction benefits both species.
Interactions in Communities (cont.)
Interaction
Expected Outcome
Competition (-, -)
Abundance of both species
decreases
Predator abundance increases,
prey abundance decreases
Parasite abundance increases,
host abundance decreases
Predation (+, -)
Parasitism (-,-)
Commensalism (+, 0)
Abundance of one species
increases; the other does not
Mutualism (+, +)
Abundance of both species
increases
Ecological Niche
• The spatial location where a species is
found is called its habitat.
• The ecological niche of a species is the
combination of its role in a community, its
habitat, and interactions with other
organisms.
Competition
• Competition for limiting resources
contributes to the niche of each species
and community structure.
• The competitive exclusion principle states
that since no two species can occupy the
same niche, one species will eventually
die out.
Competition (cont.)
Competition (cont.)
• Competition for resources can also lead to
resource partitioning, meaning that the two
species utilize different aspects of the
niche so they can both survive.
• Character displacement can also occur as
organisms evolve different characters to
adapt to aspects of a niche.
Competition (cont.)
Mutualism
• In mutualism, both species benefit from
the interaction.
• Mutualism leads to an intricate web of
interdependency critical to community
structure.
Community Stability
• Communities rely upon one or more
species called keystone species that
stabilize the structure of a community.
Native Versus Exotic Species
• Native species are those indigenous to an
area.
• Invasive species, sometimes called exotic
species, are introduced into an area and
displace native species.
31.2 Ecology of Ecosystems
• The populations of an ecosystem are
described in terms of their food source.
• Autotrophs, also called producers,
produce their own food.
– Photoautotrophs use the sun to make their
own food.
– Chemoautotrophs obtain energy to make food
by oxidizing inorganic compounds.
31.2 Ecology of Ecosystems
(cont.)
• Heterotrophs (consumers) must consume
the nutrients synthesized by autotrophs to
survive.
– Herbivores graze on plants.
– Carnivores eat meat.
– Omnivores eat both plants and meat.
– Decomposers break down dead organic
matter (detritus).
Energy Flow and Chemical
Cycling
• The autotrophs and heterotrophs of a
community create a flow of energy and
nutrients through an ecosystem.
• As energy flows from one level of an
ecosystem to the next, a large fraction
(about 90%) is lost, generally as heat.
Energy Flow and Chemical
Cycling (cont.)
Energy Flow
• The energy flow through an ecosystem can be
illustrated as a food web or food chain.
– A grazing food web begins with plants.
– A detrital food web begins with detritus.
• The level of nourishment within a food web or
chain is called a trophic level.
• Since energy is lost as energy moves from one
trophic level to the next, the flow of energy can
be depicted as an ecological pyramid.
Energy Flow (cont.)
Energy Flow (cont.)
Chemical Cycling
• The pathways by which organisms move
nutrients within ecosystems create
biogeochemical cycles.
– For a sedimentary cycle, nutrients originate in
sediments or soils and cycle from autotrophs
to heterotrophs before being returned by
decomposers.
– In a gaseous cycle, the nutrient originates in
and is returned as a gas.
Chemical Cycling (cont.)
• A large fraction of nutrients may be found in
reservoirs that are unavailable to organisms.
• Organisms generally acquire nutrients from an
accessible source called an exchange pool.
• Human activities have both positive and
negative effects on the pools of nutrients.
Chemical Cycling (cont.)
Phosphorus Cycle
• Phosphorus in the environment is released as
rocks and weather, releasing phosphate.
• Producers such as plants and algae utilize
phosphate in their metabolism.
• Consumers acquire phosphate by eating
producers.
• Phosphate is returned to the ecosystem during
decomposition of producers and consumers.
Phosphorus Cycle (cont.)
Nitrogen Cycle
• Producers can use different forms of
nitrogen from the environment.
– Ammonium (NH4+) found naturally or derived
from N2 by nitrogen fixation
– Nitrate (NO3-), produced from ammonium by
nitrification
• In the nitrogen cycle, nitrification is
counterbalanced by denitrification and
nitrogen fixation.
Nitrogen Cycling (cont.)
Carbon Cycle
• There are two primary sources of carbon
for the carbon cycle.
– Gaseous or dissolved carbon dioxide
– Inorganic carbonate
• Much of the Earth’s carbon is tied up in the
bodies of organisms or in limestone and
carbonate shells.
Carbon Cycling (cont.)
31.3 Ecology of Major Ecosystems
• The Earth’s biosphere is composed of
both aquatic and terrestrial ecosystems.
– Aquatic ecosystems are both freshwater and
marine.
– The different terrestrial ecosystems are called
biomes.
Primary Productivity
• Ecosystems can be compared on the
basis of their primary productivity, which is
the rate by which producers capture and
store energy.
• Several factors influence the primary
productivity of an ecosystem.
– Temperature
– Moisture
– Nutrient availability
Primary Productivity (cont.)