As you probably know, a simple definition of biodiversity is how many species live in a particular area. Lots of things can influence biodiversity. For example, an area in the pine forests of northern North America will probably have a lot fewer species than the same size area in the tropical rainforests of Brazil.

One reason is that fewer species may have adaptations that let them live in the harsh climate of the far north. If most of the trees are the same kind, there will be fewer types of animals that can live on them. For example, if there are many types of trees—as in the rainforest, each might have a lot of specialized insects and other animals living on it. If almost all the trees are blue spruce trees, there will only be animal species that specialize in, or at least do okay on blue spruce.

Another reason has to do with productivity (how much photosynthesis is going on). If there’s plenty of water and sunlight, a lot of photosynthesis can happen (if it’s not limited by other things, such as nutrients). In cold places, the water may be frozen for months, making for a short growing season. This matters because less plant material to eat means fewer consumers. Fewer individuals can mean fewer species because there’s a minimum sustainable population size for any species.

The size of the habitat also matters. If it takes 100 square miles to support a mountain lion, you need a lot of habitat to support a sustainable mountain lion population. Deforestation decreases the size of available habitat and also breaks it up (fragments it) into small pieces that may not support the animals.

There’s an excellent video of this concept at this link. It’s called Ants to Grizzlies. Which species do you think are harmed more by deforestation, ants or grizzlies?