Ecology hw trophic - homework questions with answers PDF

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Gina Schipani 11/1/16 Ecology Homework

Questions: 1. What is a parasite? What are the general consequences of a parasitic interaction to the parasite and the host species? 

A parasite is an organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense.

2. According to the article, what are some reasons parasites are often challenging to observe? 

Parasites live secretively being invisible to the outside world with some exceptions like tapeworms, parasites tend to be very small.

3. What is a “free-living” species (provide a definition)? 

An organism that is not directly dependent on another organism for survival.

4. Are parasites important in shaping community structure? If so, provide at least two general examples of how they shape community structure. 

“Parasites also influence host behavior and fitness, and can regulate host population sizes, sometimes with profound effects on trophic interactions, food webs, competition, biodiversity and keystone species. These interactions suggest that parasites are integral components in shaping community- and ecosystem structure.”

5. What type of trophic interaction is displayed in Figure 1? 

Secondary consumer.

6. Why are predators on islands in the Gulf of California more abundant on islands with sea bird colonies? 

“Predators on islands in the Gulf of California, including lizards, scorpions and spiders, are one- to two orders of magnitude more abundant on islands with sea bird colonies because they feed on bird ectoparasites.”

7. What is trophic transmission? What are some consequences to a host species from the trophic transmission of a parasitic species? 

Trophic transmission is in which the parasite manipulates the behavior of its host to increase transmission success to higher trophic levels. Parasites that use trophic transmission have complex life cycles, requiring more than one host species to procreate. Parasites that infect new hosts through trophic transmission frequently alter their host's behavior or morphology in ways that increase predation risk, thereby aiding the parasite in reaching the next host in its life cycle

8. Why were parasites typically excluded from food webs? If parasites are included in food webs and other studies on trophic interactions, could they be considered keystone species? Why or why not? 

Integrating parasites into food webs also suggests that the classical Eltonian pyramid may need to be revised: if parasites feed at a trophic level above their hosts, parasites would occupy the pinnacle of this new pyramid, which would be a significant departure from the traditional placement of top predators at the peak of the food chain. I don’t feel that they can be considered a keystone species because yes they help some species but they also harm too, and species can still live without them.

9. Why are mid-trophic levels of food webs most susceptible to natural enemies when including parasites in food webs? 

Incorporating parasites into food webs reveals that mid-trophic levels are most susceptible to natural enemies because this group is at risk from both predators and trophically transmitted parasites.

10. How can parasitic interactions influence biodiversity? 11. Parasites can influence biodiversity when they alter the outcome of competitive interactions between host species, a phenomenon termed parasite-mediated competition. In some cases, this occurs when a tolerant host species amplifies a parasite's abundance, causing an indirect negative effect on a second, less tolerant host species. Parasites can also positively contribute to biodiversity by allowing a competitively inferior species to coexist with a dominant species. 12. According to the article, what type of species are Diadema urchins? What were the ecological consequences to coral reefs from the microbial pathogen (parasite) infection of these urchins? 

“Diadema urchins in the Caribbean experienced a massive die-off associated with microbial pathogens, eliminating the keystone roles of urchins as grazers and bioeroders on coral reefs. Reefs in affected regions became overgrown with algae that displaced mature corals and prevented new coral settlement. In the most extreme examples, algal cover jumped from near 1% prior to the disease outbreak, to 95% in the following two years. Nearly twenty years later, Diadema populations recovered on some Jamaican reefs, and a shift back to a coral-dominated ecosystem has begun.”...