Transcript Community ecology

Community ecology
Community ecology
• A biological community is an assemblage
of all the populations of organisms living
close enough together for potential
interaction. A community can be described
by its species composition.
• In other words, a community consists of all
the populations of different kinds of
organisms that interact in a particular
location.
Community ecology
• Ecologists define the boundaries of the
community according to the research
questions they want to investigate.
• All community boundaries are artificial.
However, defining boundaries – even if
they are artificial—is important, because it
allows us to focus on the changes that
occur in a particular area, recognize
patterns and trends, and make
predictions.
• Each community has a particular
combination of producers, consumers and
decomposers, which interact in many
ways.
• Within the community, each species is a
specialist in certain aspects of community
function. One of the ways that organisms
interact is by feeding on one another.
• Most organisms in a community participate
in several food chains. When we
recognize that many food chains in an
area overlap, we see a pattern of
interactions we can call a food web.
• The niche of an organism is its specific
functional role in its community.
• A complete description of an organism’s
niche involves a detailed understanding of
the impacts an organism has on its biotic
and abiotic surroundings, as well as all
the factors that affect the organism.
The niche of an earthworm includes how an
earthworm is affected by abiotic factors such
as the size of soil particles, soil texture,
moisture, pH, and temperature.
Its niche includes biotic factors such as parasites
that infect earthworms; birds, moles, and shrews that
eat earthworms; dead plant material that earthworms
use for food, and anglers who use worms as bait.
They transport minerals and nutrients from deeper soil
layers to the surface, bury seeds, incorporate organic
matter into the soil, and create burrows, which allow air
and water to penetrate the soil more easily.
• The habitat of an organism is the kind of
place or community in which it lives. Each
organism has particular requirements for
life and lives where the environment
provides what it needs.
• Habitats are usually described in terms of
a particularly significant feature.
Interactions
• Organisms engage in interspecific
interactions—relationships with
individuals of other species in the
community—that greatly affect population
structure and dynamics.
• In the table below, interspecific interactions
are classified according to the effect on the
populations concerned, which may be
helpful (+) or harmful (‒).
Competition
• Members of a population may compete for
limited resources such as food or space.
Interspecific competition occurs when
populations of two different species compete
for the same limited resource.
• In general, the effect of interspecific
competition is negative for both populations
(‒/‒). However, it may be far more harmful for
one population than the other.
• Interspecific competition is responsible for
some of the disastrous effects of introducing
non-native species into a community.
Mutualism
• Mutualism is a relationship in which two
species derive some benefit from each
other. Some mutualistic relationships are
so close that neither species can survive
without the other.
• Pollination is one of the most important
mutualistic relationships on Earth.
Mutualism
• Acacia trees in
Central America have
a mutualistic
relationship with
certain types of ants.
The trees provide
food and shelter to
the ants, and the ants
defend the tree from
insect herbivores.
Mutualism
• (a)The British soldier lichen in this photograph
consists of a mutualistic association between a
fungus and an alga.
• (c)Insects obtain nectar from plants; the plants
benefit by being pollinated. (Note the yellow pollen
on the bee.)
Commensalism
• Commensalism is a relationship in which
one organism benefits and the other is not
affected.
• The grey
Spanish moss
hanging on this
oak tree does
not harm the
tree but
benefits from
using the tree
surface as a
place to grow.
Parasitism
• Parasitism is a relationship in which one
organism is harmed (host) while the other
organism benefits (parasite). Parasitism
usually does not result in the immediate
death of the host.
• Generally, the parasite feeds on the host
for a long time rather than kills it.
Parasitism
• Parasites such as aphids, lice, leeches,
fleas, ticks, and mosquitoes that remain on
the outside of their host are called
ectoparasites or external parasites.
• The tick is an
external parasite that
sucks body fluids
from its host.
• An ectoparasite such
as a tick feeds while
attached to a host’s
external surface.
Parasitism
• Parasites that live inside the host’s body
are called endoparasites or internal
parasites. Familiar endoparasites are
roundworms and tapeworms.
• Tapeworms are internal parasites in the
guts of their host, where they absorb food
from the host’s gut.
Parasitism
• Parasites can have a strong negative impact
on the health and reproduction of the host.
Hosts have evolved a variety of defenses
against parasites.
• Skin is an important defense that prevents
most parasites from entering the body. Tears,
saliva, and mucus defend openings through
which parasites could pass, such as the
eyes, mouth, and nose. Finally, the cells of
the immune system may attack parasites that
get past these defenses.
Predation or Prey-Predator
• Predation is an interaction in which one
animal captures, kills, and eats another
animal.
• The organism that is killed is the prey, and
the one that does the killing is the
predator.
• Predators benefit from the relationship
because they obtain a source of food;
obviously, prey organisms are harmed.
• Most predators are relatively large,
compared to their prey, and have specific
adaptations to aid them in catching prey.
Herbivory
• Herbivory is consumption of plant parts or
algae by an animal. Although herbivory is
not usually fatal, a plant whose body parts
have been eaten by an animal must
expend energy to replace the loss.
Herbivory
• Consequently, numerous defenses against
herbivores have evolved in plants. Thorns
and spines are obvious anti-herbivore
devices, as anyone who has plucked a
rose from a thorny rose-bush or brushed
against a spiky cactus knows.
Conservation Biology
• Conservation biology is a goal-oriented science
that seeks to understand and counter the loss of
biodiversity.
• Some conservation biologists focus on protecting
populations of threatened species.
• This approach requires an understanding of the
behavior and ecological niche of the target
species, including its key habitat requirements and
interactions with other members of its community.
• Threats posed by human activities are also
assessed.
• With this knowledge, scientists can design a plan
to expand or protect the resources needed.
Overview: Striking Gold
• Scientists have described over 1.7 million of
the world's species of animals, plants and
algae, as of 2010.
Overview: Striking Gold
Overview: Striking Gold
• Tropical forests contain some of the greatest
concentrations of species and are being
destroyed at an alarming rate
• Humans are rapidly pushing many species
toward extinction
To learn about others, visit the International Union for
Conservation of Nature and Natural Resources web
site at
www.iucnredlist.org
The Loss of Biodiversity
• Loss of biodiversity
includes the loss of
ecosystems, species,
and genes. While
valuable for its own
sake, biodiversity
also provides food,
fibers, medicines,
and ecosystem
services.
• Ecosystem Diversity : The world’s
natural ecosystems are rapidly
disappearing. Nearly half of Earth’s forests
are gone, and thousands more square
kilometers disappear every year.
• Aquatic ecosystems are also threatened.
For example, an estimated 20% of the
world’s coral reefs, ecosystems known for
their species richness and productivity
have been destroyed by human activities,
and 15% are in danger of collapse within
the next two decades.
Bison
• As natural ecosystems are lost, so are
essential services.
• Water purification is one of the services
provided free of charge by healthy
ecosystems. As water moves slowly
through forests, streams, and wetlands,
pollutants and sediments are filtered out.
• Whether taken from surface waters such
as lakes or subsurface sources
(groundwater), the drinking water supplied
by public water systems typically has
passed through this natural filtration
process.
• Species Diversity : When ecosystems
are lost, populations of the species that
make up their biological communities are
also lost.
• Nations have enacted laws to protect
biodiversity, and an international
agreement protects some 33,000 species
of wild animals and plants from trade that
would threaten their survival.
• Species loss also has practical
consequences for human well-being.
• Many drugs have been developed from
substances found in the natural world,
including penicillin, aspirin, antimalarial
agents, and anticancer drugs.
• Dozens more potentially useful chemicals
from a variety of organisms are currently
being investigated.
• Genetic Diversity : The genetic diversity
within and between populations of a
species is the raw material that makes
micro-evolution and adaptation to the
environment possible—a hedge against
future environmental changes.
• If local populations are lost and the total
number of individuals of a species
declines, so, too, do the genetic resources
for that species. Severe reduction in
genetic variation threatens the survival of
a species.
Causes for loss of biodiversity
• Habitat destruction
Human alteration of habitats poses the
single greatest threat to biodiversity throughout
the biosphere. Agriculture, urban development,
forestry, mining, and environmental pollution
have brought about massive destruction and
fragmentation of habitats. Deforestation
continues at a blistering pace in tropical and
coniferous forests
Fig. 56-2
• Invasive species
Invasive species, which disrupt communities by competing with, preying on, or
parasitizing native species. The lack of
interspecific interactions that keep the
newcomer populations in check is often a
key factor in a non-native species becoming
invasive
• Over-exploitation
Over-exploitation of wildlife by
harvesting at rates that exceed the ability of
populations to rebound. Such
overharvesting has threatened some rare
trees that produce valuable wood, such as
rosewood. Animal species whose numbers
have been drastically reduced by excessive
commercial harvest, poaching, or sport
hunting include tigers, whales, rhinoceroses.
• Pollution
Pollutants released by human activities
can have local, regional, and global effects.
Some pollutants, such as oil spills,
contaminate local areas.
• Pollution
Recently, scientists have recognized a
new type of aquatic pollutant: plastic
particles that are small enough to be eaten
by zooplankton. Many body washes and
facial cleansers include plastic “microbeads”
to boost scrubbing power. Too small to be
captured by wastewater treatment plants,
these microparticles enter the watershed
and eventually wash out to sea.