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Friday, June 8

  1. page Community Ecology edited ... Species Diversity and trophic structure Two fundamental features of community structure are s…
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    Species Diversity and trophic structure
    Two fundamental features of community structure are species diversity and feeding relationships. Species diversity is the variety of life forms that make up the community. It is dependent on both the species richness and the
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    relative abundance of different species. Species richness is defined as the total number of different species in the community. Relative abundance is the proportion each species represent of the total individuals in the community. Diversity can be compared using a diversity index, which is based on species richness and relative abundance. One commonely used index is the Shannon diversity index (H) which states:
    H = –(pA ln pA + pB ln pB + pC ln pC + …)
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    Bottum-Up and Top-down models
    The bottom-up model proposes V --> H linkages, in which the presence or absence of mineral nutrients (N) controls plant (V) numbers, which control herbivore (H) numbers, which control predator (P) numbers. Basically:
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    top-down model postulatesstates that it
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    uptake of nutrients during growth and reproduction. Simplified, the model is N <-- V <-- H <-- P.
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    nutrients during growth and reproduction. Simplified, the model is N <-- V <-- H <-- P.
    Biomanipulation can help restore polluted communities by using the top-down model.
    In a Finnish lake, blooms of cyanobacteria (primary producers) occurred when zooplankton (primary consumers) were eaten by large populations of roach fish (secondary consumers).
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    Disturbance influences species diversity and composition
    A long time ago, ecologists agreed with the fact that communities are in a state of equilibrium, but the nonequilbrium model states otherwise. the nonequilibrium modeldescribes communities as contantly changing after being buffeted by disturbances.
    A disturbanceisdisturbance is an event
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    intermediate disturbance hypothesissuggestshypothesis suggests that moderate
    •High levels of disturbance exclude many slow-growing species
    •Low levels of disturbance allow dominant species to exclude less competitive species
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    after a disturbance.
    Primary succession occurs where no soil exists when succession begins.
    Secondary succession begins in an area where soil remains after a disturbance.
    Human Disturbance
    Humans have the greatest impact on biological communities all over the world. Humam
    disturbance to communities reduce species diversity. Humans turn tropical forests ito vast barren areas for lumber, cattle grazing, and farmland. The boats that drag nets on the seafloor to scrape up life forms in the ocean is a major disturbance in marine ecosystems.
    Biogeographic factors affect community diversity
    Latitude and area two key factors that effect a community's species diversity. {Capture4.JPG}
    Species richness is especially great in the tropics and generally declines along an equatorial-polar gradient.
    Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate.
    Temperate and polar communities have started over repeatedly following glaciations
    The greater age of tropical environments may account for the greater species richness
    In the tropics, the growing season is longer such that biological time is faster
    Climate is likely the primary cause of the latitudinal gradient in biodiversity.
    Two main climatic factors correlated with biodiversity are solar energy and water availability.
    They can be considered together by measuring a community’s rate of evapotranspiration.
    Evapotranspiration is evaporation of water from soil plus transpiration of water from plants.
    The species-area curve tells the idea that, all other factors being equal, a larger geographic area has more species.
    A species-area curve of North American breeding birds supports this idea.
    Island Equilibrium Model
    Species richness on islands depends on island size, distance from the mainland, immigration, and extinction.
    The equilibrium model of island biogeography that species richness on an island levels off at a dynamic equilibrium point.
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    Pathogens
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    Pathogens alter and drastically change communities. For an example. coral reef communities are being hit by the white-band disease, which is decimating them. Zoonotic pathogens have been transferred from other animals to humans. The transfer of pathogenscan be direct or through an intermediate species called a vector. Many of today’s emerging human diseases are zoonotic. Avian flu is a highly contagious virus of birds. Ecologists are studying the potential spread of the virus from Asia to North America through migrating birds.
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Thursday, June 7

  1. page Community Ecology edited ... The addition of pike perch (tertiary consumers) controlled roach populations, allowed zooplank…
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    The addition of pike perch (tertiary consumers) controlled roach populations, allowed zooplankton to increase and ended cyanobacterial blooms.
    Disturbance influences species diversity and composition
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    by disturbances. A
    A
    disturbanceis an
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    of disturbance.
    •High levels of disturbance exclude many slow-growing species
    •Low levels of disturbance allow dominant species to exclude less competitive species
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    a disturbance
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  2. page Community Ecology edited ... Bottum-Up and Top-down models The bottom-up model proposes V --> H linkages, in which the …
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    Bottum-Up and Top-down models
    The bottom-up model proposes V --> H linkages, in which the presence or absence of mineral nutrients (N) controls plant (V) numbers, which control herbivore (H) numbers, which control predator (P) numbers. Basically:
    ...
    <-- P.
    Biomanipulationcan

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    Biomanipulation can
    help restore
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    top-down model. In
    In
    a Finnish
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    (secondary consumers). The
    The
    addition of
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    cyanobacterial blooms.
    Disturbance influences species diversity and composition
    A long time ago, ecologists agreed with the fact that communities are in a state of equilibrium, but the nonequilbrium model states otherwise. the nonequilibrium modeldescribes communities as contantly changing after being buffeted by disturbances. A disturbanceis an event that changes a community, removes organisms from it, and alters resource availability. Fire is a significant disturbance in most terrestrial ecosystems. The intermediate disturbance hypothesissuggests that moderate levels of disturbance can raise greater diversity than either high or low levels of disturbance.
    •High levels of disturbance exclude many slow-growing species
    •Low levels of disturbance allow dominant species to exclude less competitive species
    Ecological succession is the sequence of community and ecosystem changes after a disturbance

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  4. page Community Ecology edited ... Two fundamental features of community structure are species diversity and feeding relationship…
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    Two fundamental features of community structure are species diversity and feeding relationships. Species diversity is the variety of life forms that make up the community. It is dependent on both the species richness and the
    {Capture.JPG}
    ...
    which states:
    H = –(pA ln pA + pB ln pB + pC ln pC + …)
    where A,B,C are the species, p is the relative abundance of each species, and ln is the natural logarithm.The higher H is, the more diverse the community is.
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    microbial diversity.
    Diversity and Community Stability
    Ecologists change diversity in experimental communities to study the potential benefits of diversity. For example, plant diversity has been manipulated at cedar Creek Natural History Area in Minnesota for two decades!
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    --More resistant to invasive species, organisms that become established outside their native range.
    Trophic structure
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    a community. In any biological system—a habitat (a pond, an oak forest, a high plains desert, a shallow underwater reef, etc)--whatwhat defines different
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    a pyramid. Food energy is transferred from primary producers to primary consumers. then from primary consumers the secondary, tertiary, and quaternary consumers. Food chains link trophic levels from producers to the top carnivores. A food web is a series of food chains. Specifically, A food web is a model that shows all the possible feeding relationships between organisms living in an ecosystem.
    Food webs can be simplified by:
    –-Grouping species with similar trophic relationships into broad functional groups
    -–Isolating a portion of a community that interacts very little with the rest of the community
    Food chain length
    Each food chain in a food web is usually only a few links long. Two hypotheses attempt to explain food chain length: the energetic hypothesis and the dynamic stability hypothesis. The energetic hypothesis states that the length is limited by ineficient energy transfer. The dynamic stability hypothesis proposes that long food chains are less stable than short ones. Out of both the hypothesizes, most research and data support the energetic hypothesis. Certain species have a very large impact on community structure because they are highly abundant.
    Species with a large impact
    Dominant species are those that are most abundant or have the highest biomass. Because of this, dominant species exert powerful control over the occurrence and distribution of other species. For example, sugar maples have a major impact on shading and soil nutrient availability eastern North America affecting the distribution of other plant species. There is no definite explanation for why species become in control in a community, but there are hypotheses. One hypothesis suggests that dominant species are most competitive in exploiting resources. Another hypothesis is that they are most successful at avoiding predators.
    Keystone species display strong control on a community by their ecological roles or niches. In comparison to dominant species, they are not necessarily abundant in a community.
    Ecosystem engineers (or also called foundation species) cause physical changes in the environment that affect community structure. The effects of ecosystem engineers can benefit a community or give it drawbacks. As an example, beavers build damns and create ponds, which transform areas of a forest into wetlands.
    Bottum-Up and Top-down models
    The bottom-up model proposes V --> H linkages, in which the presence or absence of mineral nutrients (N) controls plant (V) numbers, which control herbivore (H) numbers, which control predator (P) numbers. Basically:
    N --> V --> H --> P. In comparison, the top-down model postulates that it is mainly predation that controls community organization. Predators limit herbivores, which limit plants, which limit nutrient levels through the uptake of nutrients during growth and reproduction. Simplified, the model is N <-- V <-- H <-- P.
    Biomanipulationcan help restore polluted communities by using the top-down model. In a Finnish lake, blooms of cyanobacteria (primary producers) occurred when zooplankton (primary consumers) were eaten by large populations of roach fish (secondary consumers). The addition of pike perch (tertiary consumers) controlled roach populations, allowed zooplankton to increase and ended cyanobacterial blooms.

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    7:12 pm
  5. page Community Ecology edited ... An interaction where a herbivore eats parts of a plant or alga is called Herbivory. The plants…
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    An interaction where a herbivore eats parts of a plant or alga is called Herbivory. The plants (prey) being eaten cannot obviously run away from predators so they may have thorns or poison in them. Predators develop features to help them find and eat plants. Many herbivourous insects have chemical sensors to help them differentiate between toxic and non-toxic plants.
    Symbiosis
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    one another.
    Parasitism is a type of symbiotic relationship between organisms of different species in which one, the parasite, benefits from a prolonged, close association with the other, the host, which is harmed. In general, parasites are much smaller than their hosts, show a high degree of specialization for their mode of life and reproduce more quickly and in greater numbers than their hosts. Classic examples of parasitism include the interactions between vertebrate hosts and such diverse animals as the tapeworms, flukes, Plasmodium species and fleas.
    Endoparasites are parasites that live within the body of their host (tapeworms or other parasitic worms) and ectoparasites are parasite that live on the external surface of a host (ticks, lice, or fleas). Some parasites change the behavior of the host to increase their own fitness. Tapeworm, for example, live inside the intestines of humans and farm animals. They obtain digested food and shelter from their hosts so the hosts are likely to suffer from malnutrition. Ticks that live on moose take blood from the moose which makes them weaks, causing hair loss. Now the moose can die from cold weather or predation by wolves.
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    Facilitation describes an interaction where one species can have positive effects on another species without direct and intimate contact. For example, the black rush makes the soil more hospitable for other plant species.
    Species Diversity and trophic structure
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    and the relative
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    relative
    abundance of
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    Relative abundance isis the proportion
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    a diversity index.index, which is based on species richness and relative abundance. One commonely
    ...
    diversity index (H) which states:
    H = –(pA ln pA + pB ln pB + pC ln pC + …)
    where A,B,C are the species, p is the relative abundance of each species, and ln is the natural logarithm.The higher H is, the more diverse the community is.
    Determining the number and abundance of species in a community is difficult, especially for small organisms. Molecular tools can be used to help determine microbial diversity.
    Diversity and Community Stability
    Ecologists change diversity in experimental communities to study the potential benefits of diversity. For example, plant diversity has been manipulated at cedar Creek Natural History Area in Minnesota for two decades!
    Communities with higher diversity are:
    --More productive and more stable in their productivity.
    --Better able to withstand and recover from environemntal stresses
    --More resistant to invasive species, organisms that become established outside their native range.
    Trophic structure
    Trophic structure is the feeding relationships between organisms in a community. In any biological system—a habitat (a pond, an oak forest, a high plains desert, a shallow underwater reef, etc)--what defines different trophic structures (or systems) is the amount of energy available to the organisms in the different trophic levels. The available energy of all/any trophic structures is almost always represented by a pyramid.

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