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Marine Communities--Lecture Notes
Terminology Groups of organisms of
the same species form a "population." Several populations
can interact together to form a "community." In a basic
(yet somewhat erroneous sense), we can also call this larger mass
of interacting populations an "ecosystem." The boundaries
are arbitrary, but should be definable. For instance, one could assess
the interactions going on in a "pier piling community" and
distinguish it from the "nearshore community." The study
of these interactions between communities (or ecosystems) and the
environment is called "ecology." Key Factors In assessing a community, it is important to try to create a checklist of the LOCATION, the CRITTERS, and the various LIFESTYLES employed. Together, this database is used to figure a flowchart of energy through the community. In more detail, the location should describe whether the populations exists on the seafloor (benthic) or swims (nektic) or drifts (planktonic). Of course, these terms are broad and the actual location should be subdefined. Similarly, one could discuss the lifestyles as "predator" or "filter feeder," but more information would allow for more detailed scrutiny. Other important factors to consider are growth rates and competition amongst individuals and populations. Carrying Capacity and Succession Once the factors are identified, it is now time to analyze the community in a dynamic view, or to let time pass. To do this, it is critical to tease out the limiting factors on the various segments of the community. If there were no limiting factors, the growth rates of individuals and populations would increase exponentially. However, there are limiting factors and they retard the growth rates. For all populations, there is an upper limit of growth imposed by the various environmental factors. This upper boundary is called the "carrying capacity." If one population is no longer successful in its lifestyle, another population may move into that role. This is called "succession." Examples of Marine Communities For the following (and any) communities, you need to be able to identify the limiting factors; nutrient pathways; ecological niches (e.g., lifestyles); competition; and transendentiality (or how long will this environment last or does it change often?). 1. Hydrothermal Vents Draw a vent. Then we will answer the following questions. 1) What are the limiting factors? (e.g., high pressure, high salinity, drastic changes in temperature, below the photic zone; open ocean, dependent on influx of nutrients coming in from hydrothermal sources). 2) Draw the nutrient pathway (very generalized). Chemosynthesis of inorganic compounds fuel modified primary consumers which in turn feed secondary consumers whose bodies are recycled after death (not a closed system). 3) Now, what ecological niches are there to be filled? Primary producers, sessile benthic heterotrophs, mobile benthic scavangers or predators, mobile nektic predators, degrading bacteria. 4) What are the critters? Symbiotic tube worms and bacterial colonies, large clams, mobile spider crabs, bacterial mats, grazing fish. 5) Now, what are the more detailed pathways? Bacteria harbored within tube worms synthesize chemical compounds and transfer energy to tubeworms. Clams filter feed the rain of detritus which is also utilized by chemosynthetic bacterial mats. Mobile scavengers and predators move amongst the colonies grazing on the abundant sea life in a deep ocean world that would otherwise be nearly devoid of biomass. Other bacteria degrade the decaying organic matter. 2. Coral Reefs Draw a reef. Again, answer the following questions (this time due it on your own; class answers will be posted later). 1) What are the limiting factors? 2) Draw the nutrient pathway (very generalized). 3) Now, what ecological niches are there to be filled? 4) What are the critters? 5) Now, what are the more detailed pathways.
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