habitat: the area where an animal, plant or microorganism lives and finds the nutrients, water, sunlight, shelter, living space and other essentials it needs to survive. Habitat loss, which includes the destruction, degradation and fragmentation of habitats, is the primary cause of biodiversity loss.
Halichondria: a sponge genus from New England.
heat-trapping gas: any of several dozen gases in Earth's atmosphere that absorb infrared energy radiated back from Earth. The two major gases are water vapor and carbon dioxide; others include methane, chlorofluorocarbons and nitrogen oxides.
herbivores: animals that eat mainly plants.
herbivorous: plant and algae eating, non-meat eating.
hermaphrodites: animals or plants having both male and female reproductive organs.
heyday: the period of greatest prosperity or productivity.
hormones: chemical substances secreted by organs or parts of the body, especially the endocrine glands, into the bloodstream. Each hormone has a specific regulatory or functional effect.
hybrid-electric vehicle (HEV): a vehicle with a dual power system, usually a conventional internal combustion engine that runs on gasoline and an electric motor powered by batteries. HEVs are more fuel-efficient and emit fewer pollutants than conventional vehicles.
hydroelectric: relating to electric energy produced by moving water.
hydrogen sulfide: a colorless gas that smells like rotten eggs and can result from the breakdown of organic matter by bacteria in the absence of oxygen.
hydrologist: a scientist who specializes in the dynamics of watershed functions and land use.
hypothesis: a statement consisting of an action (that can be tested) and a predicted result. Making a hypothesis is part of scientific inquiry.