Ecology - SAT Subject Test in Biology

The chaparral biome is known for being rather dry and for having these characteristics. They are different than deserts, as deserts do not have a rainy season. While savannas are often warm, they have a longer 6-8 month rainy season.

Abiotic factors are non-living and molds are living.

Ecosystems are composed of communities and communities are composed of populations. A biome is a larger unit than an ecosystem, as it includes multiple ecosystems.

The characteristics listed describe a savanna. Deserts can also have pronounced periods of rain and dryness but are not dominated by grasses and not populated by large migratory animals. Tropical rainforests and deciduous forests are dominated by trees and tundras tend to be colder and may not receive much rainfall, but often have moist soil due to low evaporation rates.

The taiga biome is the largest biome in the world and is characterized by short, rainy summers coupled with long, freezing winters. Due to its extremely cold temperatures, the taiga's flora or plant life consists of mostly coniferous trees that can survive on the scarce nutrients available in the cold climate of the biome. In contrast, the tundra is frozen year-round and permafrost prevents any trees from growing. Deciduous forests, as the name suggests, sports mainly deciduous trees as its plant life. The alpine biome consists mostly of the areas right below the snow lines of mountains and is generally dry year-round. The chaparral is a relatively small biome that is characterized as being mostly hot and dry year-round, with mild winters.

R-strategists are known for producing large numbers of offspring, though few live to maturity. This is a result of low parental investment, competition, etc. Despite such a large number of offspring, the gestation period for these species is generally shorter than that of K-strategists. For instance, the gestation period of mice is much shorter than the nine months seen in humans.

External process also affect the ecosystem. For example, climate is a very important external factor that will affect temperature and precipitation within the ecosystem.

"k" and "r" refer to two different reproductive strategies. K-strategists tend to occupy a more stable environment and have a larger body size as adults and at birth, fewer offspring, longer life spans, more efficient use of energy, later age of reproduction, slower maturation, more parental care, and longer gestation times. The question asked which characteristic is not generally true of k-strategists, and the correct answer is "shorter life spans," which describes r-strategists instead.

Density-dependent factors are factors that affect population growth only when the population reaches a certain level, and are strongest in a large, dense population and weakest in small, scattered populations. Disease, parasitism, competition, and predation all vary with population density. Natural disasters are the one choice that are density-independent, meaning they affect all populations similarly regardless of size/density.

Abiotic factors are the non-living components of an ecosystem. Biotic factors are living things, such as vegetation (the correct answer because it is the only living thing among the answer choices and therefore NOT abiotic).

This is an example of ecological succession. While climax community may seem like a reasonable answer, the text describes the entire process from barren rock onwards and does not specifically state that new species are no longer appearing on the island and that the community is stable. Evolution occurs within a species, and while the species on the island may change, the species themselves are not described as changing. This question mentions nothing about genetics, thus we cannot determine whether or not a population bottleneck (a reduction in population that is sudden and reduces genetic diversity) is occurring and we have no evidence that one is.

A primary consumer is any animal that consumes primary producers (autotrophs). Autotrophs consist of any creatures that create their own energy (in the form of sugars) from sunlight. Grass and algae would be considered autotrophs. Deer are the only animals shown here that consume autotrophs and are, therefore, primary consumers.

A mushroom is a decomposer and not a producer. All of the other options are photosynthetic producers.

A primary consumer is a herbivore that consumes only producers or autotrophs. For this question, rabbits only eat plants and so they would be considered the primary consumers. Grass and other organisms that can manufacture their own food are classified as primary producers. Snakes and hawks hunt other animals (such as rabbits) for food, so they must be at least secondary consumers. Fungi break down dead organisms for nutrition and are thus classified as decomposers.

Lack of competition and predators allow invasive species to thrive and increase in population number. While diet may affect a population's success in inhabiting a new environment, it is not necessarily a reason for increased success in invasive species.

This is an example of commensalism as one species benefits (the remora) and the other species is not affected (the shark). The remora gains food and has to use little energy to obtain that food whereas the shark does not notice the small remora riding on its skin. The remora does not prey on the shark, the two are not in competition with each other because the remora consumes discarded food, and the remora does not harm the shark, so it is not a parasite.

The term refers to all living organisms and can directly or indirectly lower the fitness of the other individual. A competitor may or may not go extinct. It is also possible that one species or community will exploit a slightly different niche over time to avoid competition or lessen its effects or the affect of competition may be enough to reduce population numbers but not cause the species to go extinct entirely.

Mutualism, parasitism, and commensalism are all symbiotic relationships (close, long-term interactions between two species). Parasitism correctly describes a symbiotic relationship in which one organism benefits and another is harmed (for example, giardia is a parasite found in contaminated water that can live in human intestines and cause gastrointestinal distress). Mutualism describes a relationship in which both species benefit from the interaction. Competition describes an interspecies (or intraspecies) relationship in which two species (or two members of the same species) occupying the same habitat compete for resources and the fitness of one species is harmful to the other (for example, two male deer competing to establish a dominance hierarchy or an invasive plant species taking nutrients from a native species). Commensalism describes a relationship in which one organism benefits and another organism neither benefits nor is harmed (for example, a cattle egret eating insects as it follows grazing cattle). Divergent evolution is not an interspecies relationship but an evolutionary concept by which the accumulation of differences between groups can lead to the formation of new species, often due to species diffusion to different, isolated environments.

A mutualistic relationship is a type of interspecies interaction in which both of the participating organisms gain some sort of benefit. In this case, the bee benefits by receiving food from the flower in the form of nectar. The flower, in turn, is provided with a means of pollination when the bees transport pollen from flower to flower as they gather nectar. Barnacles and whales is an example of commensalism, since the barnacles benefit without either helping nor harming the whales. Dogs and fleas is and example of parasitism, since the dog is harmed while the fleas benefit. Ospreys and fish is an example of a predator-prey relationship, as the osprey hunts the fish for food. Algae and sunlight is not a viable choice for a mutualistic relationship as the sun is not an organism.