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.

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.

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.

Egg-laying mammals are rare, and are called monotremes (order monotremata). Marsupials are mammals that bear live young who continue to develop in a pouch. Most mammals are placental (such as humans), with live births and a placenta that facilitates nutrient and waste exchange between the mother and the fetus. Prokaryotes are microscopic single celled organisms lacking distinct nuclei and organelles. Autotrophs are organisms who make their own food (organic raw material) from inorganic energy sources.