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relationships between the species that creates robustness. So, mathematical

scientists have developed measures that account for the spatial distribution of

species.

That doesn’t capture everything, though, because those species also have

to occur in appropriate numbers. A forest that is almost all pine, with a few trees

from a variety of other species sprinkled evenly throughout, isn’t biodiverse, even

though it may contain a large number of species that are well distributed. But

equal numbers of individuals of different species also may not be appropriate:

You don’t want to have the same number of lions as zebras. So, mathematical

scientists have helped to develop measures that capture the appropriateness of

the distribution of individuals among species. Developing these preliminary ideas

further will require close collaboration with biologists to produce new and more

intricate methods designed to handle problems that address the wide variety of

criteria that will enter into a more sophisticated definition of biodiversity.

Such more sophisticated measures can be derived by examining the

entire food web. By mapping out the relationships of who eats whom and

analyzing the resultant graph, teams of mathematical scientists and ecologists

can ask questions like: If you were to eliminate a group of animals, would the

network structure collapse? Which species are critical to the overall robustness

of the connections in the food web? Is present biodiversity a good predictor of

future biodiversity?

Each of these questions captures a different aspect of biodiversity, and all

of them are relevant in different contexts. Scientists have sensibly abandoned the

idea that they may find the one true perfect definition, and instead they use each

definition to get a different view of the overall issue of diversity. That raises the

challenge, however, of finding systematic ways of combining the measures.

Furthermore, current measures are rather crude, capturing only the least subtle

aspects of biodiversity.

Biodiversity not only indicates the health of ecosystems that we depend on

but also directly contributes to human well-being. Wild varieties of domestic crops

provide a wealth of genes with valuable properties like pest-resistance, greater

hardiness, or faster growth. Many of our pharmaceutical drugs are derived from

wild plants. Recent work has also shown that humans are more susceptible to

disease spread when biodiversity decreases. For example, forest fragmentation