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Community Ecology. Intro to Chapter. Mutualism : worker Acacia ant & Acacia tree (Costa Rica). How does the plant attract the "right" ants?. Commensalism : plant feeds larvae of ant. 55 Community Ecology. 55.1 What Are Ecological Communities?
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Intro to Chapter Mutualism: worker Acacia ant & Acacia tree (Costa Rica) How does the plant attract the "right" ants? Commensalism: plant feeds larvae of ant
55 Community Ecology • 55.1 What Are Ecological Communities? • 55.2 What Processes Influence Community Structure? • 55.3 How Do Species Interactions Cause Trophic Cascades? • 55.4 How Do Disturbances Affect Ecological Communities? • 55.5 What Determines Species Richness in Ecological Communities?
55.1 What Are Ecological Communities? all the species that live and interact in a given area
Gleason & Clements, 1920s - 1930s debated the nature of communities Henry Gleason argued that plant communities were loose associations of species each species was distributed based on its environmental requirements.
Frederick Clements argued that plant communities were tightly integrated “superorganisms.” Communities in similar areas would have the same species. Who was right?
Figure 55.1 Plant Distributions along an Environmental Gradient, Whitaker’s Study—Oregon Mts. Different combinations of plants occurred in different locations (Gleason)
Ecological Communities don’t move together as a unit-- Each species has unique interactions with its environment. So why do we care? understand how these “loose assemblages of species” function... interactions with us among other things!
Trophic Levels of Community Members based on their source of energy autotrophs Photosynthesizers or primary producers that get their energy directly from sunlight. heterotrophs consume, directly or indirectly, the energy-rich molecules made by the primary producers.
Trophic Levels: Consumers Herbivores eat plants, and constitute the ____________ level. Organisms that eat herbivores are ________________. Organisms that eat secondary consumers are ____________. ________________ eat dead bodies and waste products. (specific name)
Trophic Levels, cont. Organisms that get their food from more than one trophic level are _________. Trophic levels are not clearly distinct—so why do we use them? useful way of thinking about energy flow in a community
Food Chain vs Food Web Linear sequence in which a plant is eaten by an herbivore, which is eaten by a secondary consumer, etc. Food chains are interconnected to make food webs.
Figure 55.2 Food Webs Show Trophic Interactions in a Community
Most comm have only 4-5 trophic levels: WHY? Energy is lost between trophic levels. What kind of diagram shows this? Pyramids of energy –or- Pyramids of biomass (weight of living matter)
Figure 55.3 Diagrams of Biomass and Energy Distributions Pattern? Energy decreases from lower to higher levels
Energy diagrams are variable-- A forest has high biomass in the producer level Much energy is stored as wood (difficult to digest) that is unavailable to most herbivores. Photo 55.1 Cloud forest in Costa Rica.
What about in aquatic ecosystems? Primary producers: bacteria & protists High rates of cell division support a high biomass of herbivores, and result in an inverted biomass distribution.
Examples of Detritivores? bacteria, fungi, worms, mites, insects What do they eat/how? transform detritus (dead remains and waste products) into free mineral nutrients that can be taken up and used again by plants. How does this help nutrient cycles? Continued ecosystem productivity depends on the decomposition of detritus.
Categories of species interactions: Predation or parasitism: one participant is harmed, the other benefits. Competition: two organisms using same resource that is insufficient to supply needs of both. Mutualism: both species benefit.
Plant-animal mutualism: Pollination of a night-blooming cactus by a bat
Categories of species interactions: Commensalism: one participant benefits and the other is unaffected. Amensalism: one participant is harmed, and the other is unaffected. These interactions may increase or decrease the range of conditions over which a species can exist…how?
Animal-animal mutualism: rattle ants & small oak blue caterpillar
Parasites Parasites are usually _____________ than their hosts, and live _________ or ___________ the host. They often feed on the host without killing it. Microparasites are much smaller: bacteria, viruses, protists.
Predators typically larger, live outside the bodies of their prey. Predators of animals typically kill their prey Herbivores are predators of plants, and often do not kill the plants. Predators can reduce the size of prey populations, but predator-prey relationships are usually more complex.
Predator and prey population densities can oscillate together. Growth of predator population nearly always lags growth of prey population. WHY? As predator population grows, it reduces size of prey population, then predators run out of food and population crashes.
Figure 55.4 Hare and Lynx Populations Cycle in Nature (Part 1)
Figure 55.4 Hare and Lynx Populations Cycle in Nature (Part 2) online simulation
Testing the Model To test whether oscillations of snowshoe hare and Canadian lynx populations were due only to the interactions between the species, enclosures were built to exclude lynx, but not hares. Population cycles of the hares were influenced by food supply as well as predators.
Figure 55.5 Prey Population Cycles May Have Multiple Causes (Part 1)
Figure 55.5 Prey Population Cycles May Have Multiple Causes (Part 2)
Predators may restrict range of prey species. The Megapode Bird Story (nests) Megapodes are birds that do not incubate their eggs but instead lay them in a large mound of decomposing plants; heat from the decomposition warms the eggs. Megapodes have colonized many islands but are absent wherever there are Asian mammalian predators that eat eggs.
Figure 55.6 Megapode Distributions are Limited by Mainland Predators
Prey have evolved lots of adaptations! WHY? Make them more difficult to capture, subdue, or eat Like What? Includes toxic hairs, tough spines, noxious chemicals, camouflage, and mimicry So, have predators evolved? YES!!! Predators, in turn, have evolved more effective ways to capture prey
Mimicry is well studied—2 types? Batesian mimicry: a palatable species mimics an unpalatable or noxious species. Müllerian mimicry: two or more unpalatable or noxious species converge to look alike.
How do they persist in the ecosystem? Batesian mimicry can be maintained if the mimic is less common in the environment than the unpalatable species. In Müllerian mimicryall species in the system benefit when an inexperienced predator eats one individual, and learns to avoid individuals of all the species.
How do microparasite populations persist??? New hosts must become infected before the current host dies. Microparasites can invade a host population with many susceptible individuals Microparasite population decreases as more hosts become immune
Examples of microparasite modes of infection? breath, body fluids, water, animal vectors Infected hosts can sometimes continue to infect others, even after death. Cholera? caused by the bacterium Vibrio cholerae bacterium is ingested from water supplies thousands are released when the victim defecates.
How can competition for resources influence abundance & distribution of species? Interference competition: one species interferes with the activities of another. Exploitation competition: one species reduces the availability of a resource.
