The louse is one of these organisms which benefits at the expense of its host.

What is a parasite
It's the ecological term that describes the grass in this food web based on its role in making glucose that feeds the rest of the organisms.

What is a producer
This element makes up the majority of Earth's atmosphere.
What is nitrogen
In primary succession, this abiotic factor must develop before most plants can grow.
What is soil

It's the term that describes the 2,000 individuals within this species that this habitat can support.

Category: Human Impact
In ecosystems, this process causes the concentration of toxins like DDT to increase at each successive trophic level, often most severely impacting top predators such as bald eagle.
The chicken eats parasitic insects that could harm the pig, while the pig offers protection from predators of the chicken in this type of relationship.
What is mutualism
It's the name of each organism in the food web that could be classified as a primary consumer.

What are grasshopper, mouse, and rabbit
It's a term that describes carbon in it's energy-rich form buried for eons deep underground that is often extracted by drilling wells.
What are fossil fuels (oil, natural gas, coal, etc)
This type of succession occurs after a disturbance like a wildfire, where soil remains intact.
What is secondary succession
It's the endearing term given to a victim of a parasitic (or viral) infection.
What is a host
Ostriches have good hearing; gazelle have excellent vision. For this reason they often graze together to avoid predation. While they both benefit, they also consume the same foods, so they're considered this.
What are competitors
It's the color that represents a food chain that ends with a tertiary consumer.

What is blue
Responsible use of this lawn-enhancing chemical product is necessary to prevent too much nitrogen from entering water reservoirs that can trigger this fish-killing algae blooms.
What is fertilizer
These hardy organisms, such as mosses and lichens, are the first to colonize barren environments.
What are pioneer species
It describes an interaction where one organism kills and eats another
What is predation (or predator/prey relationship)
No harm, no "fowl". This tree doesn't seem to mind the presence of the nest as it offers a good habitat for the bird that built it. An example of this.

What is commensalism
It's the name given to the organisms not pictured in the food web, such as mushrooms and bacteria, based on their heterotrophic role in recycling nutrients.

What are decomposers
It's the respective molecular forms that carbon and nitrogen are found in the atmosphere.
What are CO2 (carbon dioxide) and N2 (nitrogen gas)
During secondary succession, this category of plants containing xylem and phloem tissues can become established relatively quickly since nutrient-rich soil is available.
What are vascular plants
This term describes the role or space a species occupies within its ecosystem
What is niche
Ectoparasites include fleas and ticks that are found outside the body. This term describes the other types, like tapeworms which live inside the body.
What are endoparasites
It's the amount of energy passed to the hawk through the yellow food chain when the grasshopper consumes 200,000 kilocalories of energy.

What is 200 kilocalories
This process, carried out by certain prokaryotes like Rhizobium in legume root nodules, converts atmospheric nitrogen gas into ammonia, making nitrogen available for plant use.
What is nitrogen fixation
This stage of succession represents a stable, mature community that undergoes little change in species composition.
What is a climax community
The position an organism occupies in a food chain
What is it's trophic level