Community Ecology

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Community Ecology

• Divya Patel, Nastassja Kosinski, Amanda Manzione,
  Renée Buttel

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Concept 53.1- A community's interactions include
competition,predation, herbivory, symbiosis, and
disease.
Competition (-/-) Competition for resources between plants, between animals, or between decomposers when resources are in short supply. An ecological niche is the sum total of a species use of the biotic and abiotic resources in its environment. The competitive exclusion principle states that two species cannot coexist in the same community if their niches are identical. Character Displacement is the tendency for characteristics to be more divergent in sympatric (geographically overlapping) populations of two species than in allopatric (geographically separate) populations of the same two species.
Predation (/-) An interaction between species in which one species, the predator, eats the other, the prey. Because of predation, many species have developed special adaptations, such as various forms of mimicry and coloration.
Herbivory (/-) An interaction in which a herbivore eats a part of a plant or an alga. Because of herbivory many plants and algae have developed many chemical toxins and physical defenses (spines and thorns), while many herbivores have developed the ability to distinguish the difference between nutritious and malnutritious plants.
Parasitism (/-) A type of symbiotic relationship in which the symbiont (parasite) benefits at the expense of the host by living either within the host (endoparasitism) or outside the host (exoparasitism). Parasitoidism is a type of parasitism in which an insect lays eggs on or in a living host the larvae then feed on the body of the host eventually killing it.
Disease (/-) Pathogens (disease- causing agents) can be bacteria, viruses, or protists, but fungi and prions can be pathogenic also. Pathogens inflict lethal harm on their hosts. Pathogens are very much like parasites.
Mutualism (/) A symbiotic relationship in which both participants benefit. Mutualistic relationships sometimes involve the evolution of related adaptations in both species, with changes in either species likely to affect the survival and reproduction of the other.
Commensalism (/0) An interaction between two species in which one of the benefits, but the neither harms nor helps the other. There few if any cases of pure commensalism.

• Interspecific Interactions and Adaptation-
  Evidence for coevolution, involving reciprocal
  genetic change by interaction populations, is
  scarce. However, generalized adaptations of
  organisms to other organisms in their environment
  is a fundamental feature of life.
• Populations are linked by interspecific
  interactions that affect the survival and
  reproduction of the species engaged in the
  interaction.

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Concept 53.2- Dominant and keystone species
exert strong controls on community structure

• Species Diversity- Species diversity measures the
  number of species in a community- its species
  richness- and their relative abundance.Species
  richness is the total number of different species
  in the community. Relative abundance is the
  proportion each species represents of the total
  individuals in the community. Measuring species
  diversity is easier said then done, there are
  very few methods used to accurately measure
  species diversity. Measuring species diversity is
  important not only for understanding community
  structure but also to conserve biodiversity.
• Trophic Structure- The structure and dynamics of
  a community depend to a large extent on the
  feeding relationships between the organisms- the
  trophic structure of the community. A food chain
  is the transfer of food energy up the trophic
  levels from its source in plants (primary
  producers) to primary consumers to secondary and
  tertiary consumers. A food web is the connection
  of many food chains it is the elaborate,
  interconnected feeding relationships in an
  ecosystem. The energetic hypothesis suggests that
  the length of a food chain is limited by the
  inefficiency of energy transfer along the chain.
  The dynamic stability hypothesis proposes that
  long food chains are less stable than short
  chains.
• Species with a Large Impact Dominant species
  and keystone species exert strong controls on
  community structure. Dominant species are the
  most abundant species in a community and their
  dominance is achieved by having high competitive
  ability. Keystone species are usually less
  abundant species that exert a disproportionate
  influence on community structure because of their
  ecological niche. Ecosystem engineers, also
  called foundation species, exert influence on
  community structure through their effects on the
  physical environment.
• Bottom-Up and Top-Down Controls- The bottom-up
  model proposed an unidirectional influence from
  lower to higher trophic level, in which nutrients
  and other abiotic factors are the main
  determinants of community structure, including
  the abundance of primary producers. The top-down
  model proposes that control of each trophic level
  comes from the trophic level above, with the
  result that predators control herbivores, which
  in turn, control primary producers.

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Concept 53.3- Disturbance influences species
diversity and composition

• Disturbance- Increasingly, evidence suggests that
  disturbance and nonequilibrium rather than
  stability and equilibrium are the norm for most
  communities. According to the intermediate
  disturbance hypothesis moderate level of
  disturbance can foster higher species diversity
  than can low or high levels of disturbance.
• Human Disturbance- Humans are the most widespread
  agents of disturbance, and their disturbance to
  communities usually reduces species diversity.
  Humans also prevent some naturally occuring
  disturbances, such as fire, which can be
  important to community structure.
• Ecological Succession- Ecological succession is
  the sequence of community and ecosystem changes
  after a disturbance. Primary succession occurs
  where no soil exists when succession begins
  secondary succession begins in a are where soil
  remains after a disturbance. Mechanisms producing
  community change during succession include
  facilitation and inhibition.

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Concept 53.4- Biogeographic factors that affect
community diversity

• Research done by Charles Darwin and Alfred
  Wallace proved that tropical habitats support
  many more species than temperate and polar
  regions. An example of this is that there are 711
  different types of tree species in Malaysia while
  there are only 50 tree species in the area north
  of the Alps in Western Europe.
• Species richness in equatorial-polar gradients
  are affected by evolutionary history and time.
• As time passes, more speciation events will
  occur, causing species diversity to increase.
• Tropical habitats are older than both polar and
  temperate regions, proving that species richness
  is more abundant in the tropics than at an
  equatorial-pole gradient.
• Biodiversity is affected by climate. Solar energy
  and water are two components of climate that
  effect biodiversity.
• The species area curve was recognized by
  Alexander von Humboldt in 1807. This curve states
  that the larger area, the greater the number of
  species.
• The amount of species living on an island is
  based on the rate of immigration and the rate of
  extinction. These rates are affected by the size
  of the Island, the amount of species living on
  the island, and the distance from the island to
  the mainland. Larger islands have lower
  extinction rates because they contain more
  resources and more diverse habitats.
• The island equilibrium model was creates by
  MacArthur and Wilson. This model shows that when
  the rate of immigration is equal to the rate of
  extinction, an equilibrium will be reached. The
  islands size and distance from its mainland
  effect species richness( at equilibrium). Many
  scientist have questioned the accuracy of this
  model.

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Concept 53.5- Contrasting views of community
structure are the subject of continuing debate

• The integrated hypothesis was created by F.E.
  Clemens, of the Carnegie Institute of Washington,
  in the early 1900s. This hypothesis states that
  a community acts as a superorganism, as a result
  of required biotic interactions .
• Then, H.A. Gleason, of the University of Chicago,
  created the individualistic hypothesis. This
  hypothesis states that species with the same
  abiotic needs live in the same area.
• These hypotheses are similar because they state
  that communities interact.
• These hypotheses differ because the integrated
  hypothesis states that species depend upon their
  interactions with other species and he
  individualistic hypothesis states that each
  species lives in an environment where the abiotic
  factors that it needs are present.
• American scientists Paul and Anne Ehrlich
  proposed the idea that all species in a community
  depend upon and affect one another.
• The rivet model proposed the idea that species in
  a community interact with species in the web of
  life. Increasing or decreasing the population of
  one species will greatly affect the population of
  another species.
• The Redundancy model was created in 1992 by Brian
  Walker, an Australian Ecologist. This model
  proposed the idea that most species are not
  associated with one another and that decreasing
  or increasing the population of one species will
  not greatly affect the population of another
  species.

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What is DDT?

• DDT is a pesticide that was released to the
  public after WWII.
• Unfortunately, during that time and even today,
  many people are unaware of the side effects of
  DDT in the environment especially on factors such
  as herbivory, predation, and interspecific
  competition.
• Thanks to the work of many researchers and
  publicists, such as Rachel Carson, people today
  are becoming aware of the effects of DDT and now
  DDT is banned for use.

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Herbivory

• Herbivory an interaction in which an herbivore
  eats parts of plants or alga
• DDT is sprayed all over plants for the purpose of
  killing unwanted insects. Because DDT is sprayed
  on plants, herbivores that eat those plants will
  take in the DDT. If the herbivores take in the
  DDT in large consumptions, then they will be
  unable to carry out necessary life functions,
  like reproduction, and eventually become extinct.
  Hence there wouldnt be anymore interaction
  between the involved plant species and their
  herbivore predators.
• Global warming also affects herbivory. Global
  warming is when the global temperature increases.
  Many organisms, especially plants that cannot
  disperse rapidly over long distances, would
  probably not be able to survive the high rates of
  climate change projected to result from global
  warming. If plants, dont survive, then neither
  will the herbivores, which are dependent on them.

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Predation

• Predation An interaction between species in
  which one species, the predator, eats the other,
  the prey.
• Predation is also affected severely by DDT. After
  DDT was released to the public, one of the first
  signs that DDT was a serious threat to the
  environment was when the population of various
  bird species, such as pelicans, ospreys, eagles,
  all birds that feed on herbivores that feed on
  plants. The accumulation of DDT in the tissues of
  these birds interfered with the deposition of
  calcium in their eggshells, a trend that may have
  already occurred because of environmental
  conditions. When these birds tried to incubate
  their shells, the weight of the parents broke the
  shells of the affected eggs, resulting a decline
  of reproduction rates. Basically, this shows how
  the interaction between predators (birds) and
  their preys (herbivores) leads to the decline in
  the population of the predator (and in some cases
  even the prey) species.
• Predation is affected by acid precipitation. In a
  study in Norway, it was found that fish were
  dying in ponds and lakes because of acid rain
  from pollutants. This would cause the whole lake
  and pond ecosystem to suffer not only due to the
  acid precipitation, but the loss of one species
  would indicate the loss of the predator species
  and eventually the elimination of certain food
  chains.

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Interspecific Competition

• Interspecific Competition competition for
  resources between plants, between animals, or
  between decomposers when resources are in short
  supply.
• DDT affects interspecific competition.
  Competition can limit herbivore numbers because
  competition may maintain herbivore numbers below
  what the vegetation could feed. But as mentioned
  earlier herbivore numbers can be easily reduced
  through DDTs affect on herbivory. This will
  immediately affect competition. The worse part is
  that competition includes more than one species,
  so if an herbivore species, which was controlled
  by the competing species is eliminated, then the
  competing species will have nothing to compete
  for and one of two things will happen
  (1)competition will end and the competing will
  find different, new preys or (2) the competing
  species will die of starvation. Basically, DDT
  has an indirect relationship with competition,
  but it still affects the outcome of interspecific
  competition.
• Competition is affected by the overloaded global
  carrying capacity because as we approach or
  exceed the carrying capacity the amount of
  available resources will not suffice for the
  amount of organisms. Hence competition will be
  brought to a new level and many species may face
  competitive exclusion.