Biodiversity: Genetic, Species, Structural and Ecosystem Diversity

Welcome to Grade 11 Biology

Picture a hike in Algonquin Park in late September. Sugar maples are turning red, a loon calls from the lake, moss covers a fallen log, and bracket fungi stick out of a dead birch. Under your boots, a single handful of soil holds millions of bacteria. All of this variety has one name: biodiversity.

This unit is about that variety. How do biologists describe it, name it, sort it into groups and measure it? Why does it keep ecosystems working? And how are people, including you, changing it? We start with the words biologists use to talk about it.

Four ways to describe biodiversity

1. Genetic diversity is variety within one species. Every lake trout has the same basic body plan, but trout from different lakes differ in their genes. Some grow faster; some tolerate warmer water. A species with high genetic diversity has more "options" when conditions change.
2. Species diversity is the variety of species in one area. It has two parts: richness (the number of species) and evenness (how evenly individuals are spread among those species).
3. Structural diversity is the variety of physical layers and structures in an ecosystem. A mature mixed forest has tall canopy trees, younger understory trees, shrubs, ferns and wildflowers, fallen logs and standing dead trees (snags). Each structure is a different place to live, feed or nest.
4. Ecosystem diversity is the variety of ecosystems in a region: Ontario has boreal forest, tundra near Hudson Bay, Great Lakes shorelines, wetlands and the Carolinian forests of the far south.

Why structure matters

More layers mean more niches. A woodpecker needs a snag to drill a nest hole. A salamander needs a moist log. An ovenbird nests on the forest floor, while a scarlet tanager forages high in the canopy. Remove the layers and those species have nowhere to live, even if the trees themselves are still standing.

Compare a natural mixed forest with a plantation, where trees of one species were planted in rows at the same time. The plantation may have just as many trees, but they are all the same height and age, so there are fewer layers and fewer niches.

Morphology: describing the form of an organism

Biologists describe living things by their morphology: shape, size, body parts and the way those parts are arranged. Good morphological descriptions use precise words and measurements instead of opinions.

• Not "a big leaf" but "a simple leaf, about 12 cm wide, with five pointed lobes and a smooth margin between the lobes."
• Not "a weird bug" but "an insect with three body sections, six jointed legs, two pairs of wings and long, thread-like antennae."

Morphology is one of the main kinds of evidence used to classify organisms, which you will do all through this unit. (DNA evidence is the other main kind; you will see it in the phylogeny lesson.)

How many species are there?

Scientists have formally described and named roughly 1.2 to 2 million species, depending on how the count is done. But most species have never been described. A widely cited 2011 study estimated that Earth may have about 8.7 million species of eukaryotes (organisms with a nucleus), and the number of bacterial and archaeal species is far less certain still. Most undescribed species are small: insects, mites, fungi, nematode worms and microbes, especially in tropical forests, soil and the deep sea.

So when you say a place has "20 species," you really mean "20 species that we found and could identify with our method." That is an important idea for reporting results honestly (A1.8).