47.1 THE NICHE IS THE ECOLOGICAL ROLE PLAYED BY A SPECIES.
47.2 COMPETITION, PREDATION, AND PARASITISM ARE ANTAGONISTIC INTERACTIONS IN WHICH ONE SPECIES BENEFITS AT THE EXPENSE OF ANOTHER.
47.3 IN MUTUALISMS, THE BENEFITS TO BOTH SPECIES OUTWEIGH THE COSTS OF PARTICIPATION.
47.4 COMMUNITIES ARE SHAPED BY THE EVOLVED FEATURES OF ORGANISMS, WHICH SHAPE THE INTERACTIONS WITH OTHER ORGANISMS AND WITH THE PHYSICAL ENVIRONMENT.
47.5 THE CYCLING OF MATERIALS AND THE FLOW OF ENERGY THROUGH ECOSYSTEMS REFLECT WAYS IN WHICH ORGANISMS INTERACT IN COMMUNITIES.
47.6 BIOMES ARE BROAD, ECOLOGICALLY UNIFORM AREAS CHARACTERIZED BY THEIR CLIMATE, SOIL, AND PLANT SPECIES.
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Choose an organism, such as an oak tree, and define its niche.
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The niche of an oak tree depends of several pieces of information, including: what type of climate/environment/resources can support an oak tree; what other types of vegetation are found alongside oak trees (and how these different plant species interact); and what organisms either feed on oak tree products, or require oak trees for shelter. An oak tree is found in a deciduous forest, which contains nutrient-rich soil and experiences a moderate climate and defined seasons. These trees provide shade, which creates an appropriate environment for underlying vegetation (i.e., ferns, shrubs). Oak trees also provide nesting spots for a variety of birds and mammals, and provide food for a variety of insects (which feed on oak leaves) and vertebrates (i.e., squirrels eat acorns).
Give an example of an antagonism and a mutualism, and in each case, describe the benefits and costs to the participants.
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The relationship between aphids and the bacteria that colonize them is an example of mutualism. Here, the bacteria benefit because they are provided with a safe environment within the aphids, and aphids benefit because their nutrient-poor diet is supplemented with products from the bacteria. Conversely, any predator-prey interaction is an example of antagonism. For example, take the relationship between seals and killer whales. Here, a killer whale benefits by gaining energy from the seals it eats (energy which is used for reproduction or other necessary life activities). Conversely, a seal that is consumed is certainly negatively affected. Once killed, the seal no longer has the opportunity to mate and reproduce, and cannot continue to spread its genetic information to the next generation.
Name three factors that help determine the species composition of a community.
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A community encompasses all of the species within a given habitat. The composition of a given community can be shaped by: 1) inter- and intraspecific competition; 2) the frequency of disturbances (like fires) occurring within an environment; and 3) seasonal changes which result in different weather patterns, as well as species’ migration.
Describe how a physical disturbance, such as a drought, can affect community composition.
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When a disturbance occurs in a given environment, it can drastically alter the composition of that area’s community. A drought can seriously reduce the population size of species not equipped to deal with the scarcity of water. This may have a similar effect as when a wildfire clears a portion of a forest. Such a change allows for new species (adapted for dry conditions) to enter and colonize an area, leading to the process of ecological succession. If droughts are common in a specific region, these disturbances can select for organisms that can tolerate a lack of water and dry conditions. This, in turn, can limit the species diversity in a given community.
Explain what is meant by “ecological succession” and give an example.
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Ecological succession describes the temporal colonization of a new habitat by different species. Each species changes that habitat, making conditions favorable for a new species to move in. A prime example of ecological succession is what occurs after a new island is formed by volcanic activity. Initial colonization by lichen (and associated invertebrates) leads to soil formation and subsequent colonization by grasses and shrubs, which eventually make way for larger trees.
Describe how herbivores can affect the abundances of organisms at higher and lower trophic levels.
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Herbivores occupy the trophic level between primary producers (i.e., plants) and predators. If there is an ample supply of vegetation, herbivores consume this plant material and reproduce. This increase in herbivore numbers provides food for predators at higher trophic levels, and results in an increase in the predator population. If herbivores exhaust the resources provided by primary producers, their numbers decrease, resulting in less food for predators and a smaller predator population. In this manner, changes in an herbivore population can influence predator and primary producer populations at different trophic levels.
Choose five biomes, describe their climate and vegetation, and explain why they differ from one another.
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Biomes include: 1) rainforests—characterized by copious amounts of rain, warm temperatures, and a diverse array of plant and animal life; 2) deserts—regions with limited precipitation, a high rate of evaporation (in some cases), and vegetation that is equipped for the long-term storage of water (i.e., cacti); 3) taiga—forests that experience a brief summer season, occur in cold climates, and are characterized by a large proportion of conifers and shrubbery; 4) deciduous forests—which experience a range of seasons and moderate rainfall, and support several different tree species; and 5) the savannah—which experiences definitive wet and dry seasons and is primarily inhabited by tall grasses.
Interestingly, the vegetation that exists in these five different biomes is constrained, in part, by evaporation and transpiration rates (which are dependent on factors such as temperature and annual precipitation). Consider the Sahara Desert in Africa. The high temperature of this desert, paired with the limited amount of rainfall, means that most water in the Sahara will evaporate pretty quickly. Any plants in the Sahara should be able to survive in an environment where water is scarce, and must maintain low transpiration rates (thus conserving precious water). These conditions limit which plants can inhabit the Sahara Desert. In other terms, since the Sahara Desert has a high evapotranspiration ratio (the comparison of the rate of evaporation to the rate of transpiration), only certain types of vegetation can survive in this environment.
Describe the general pattern of diversity from the equator to the poles. Provide two hypotheses to explain this pattern of diversity.
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Generally, greater species diversity is observed at latitudes close to the equator. This is particularly evident if we compare the species observed in rainforests (latitudes of 0–10°) to those seen in tundras (latitudes at 65° or higher) or at the northern/southern poles. Rainforests demonstrate a huge array of life, with hundreds of species of trees, insects, and other animals observed in a small area. Conversely, the tundra can only support a limited number of plants capable of surviving in a few inches of topsoil (i.e., shrubs).
Two theories can explain this difference in species diversity observed near the equator versus higher latitudes. At higher latitudes, plants and animals must survive changes in temperatures (sometimes extreme) and seasons. Few species can survive in these climates, effectively limiting species diversity. In addition, higher latitudes are relatively “new” habitats compared to those observed at the equator. The covering of northern latitudes by glaciers during the ice ages, and the subsequent recession of these glaciers, has only recently opened up these environments to colonization by new species. Regions near the equator, however, have experienced the same environmental conditions for longer periods, allowing for more species to evolve and thrive.