Definition

What is biodiversity?

Biodiversity, shorthand for biological diversity, can be defined as the variety and variability of life at all its hierarchical levels, from genetic diversity within the same species to diversity between species and through arrays of higher taxonomic levels. Biodiversity also includes the variety of ecosystems, which comprise both the communities of organisms within particular habitats and the physical conditions under which they live.

Biodiversity thus has three complementary levels:

• Genetic diversity that deals with the variety of genetic information between individuals within and between populations. 
• Taxonomic diversity (often referd to as species diversity or organismal diversity) that deals with the variation between species and higher taxonomic categories 
• Ecological diversity that encompasses the broad differences between ecosystem types, and the diversity of habitats and ecological processes occurring within each ecosystem type.

Biodiversity clearly is a multidimensional concept that can only be fully protected if understood over space and time.

Why study biodiversity?

The reason for studying biodiversity is two-fold:

• Man has (and always has had) an inherent desire to understand the past, present and future of the diversity of life that surrounds him. 
• Man has an extrinsic drive to understand how biodiversity functions and evolves because his ever-growing impact on nature clearly adversely impacts biodiversity and ecosystem functioning. This in turn leads to dramatic lowering of ecosystem services, that is, the free profits ecosystems provide to humans 

Understanding how biodiversity functions on the local, regional and global level is thus at the same time scientifically daunting and crucial to maintain human well-being.

How to study biodiversity?

Biodiversity is to be studied both on a temporal and spatial scale; both at the level of genetic diversity, the level of taxonomic diversity and the level of ecosystem diversit

Understanding of all these different, intermingled components of biodiversity demands quantifications: measurements. However the inherent complexity of biodiversity makes that no single adequate biodiversity measurement exists. For now it suffices to note that measurements generally have two components: (i) number and variety of entities; (ii) relative abundance or evenness of distribution of the entities.

On the spatial scale three levels are generally considered:

• Alpha diversity: the diversity within local assemblage, community or habitat
• Beta diversity: rate and extent of turnover of alpha biodiversity (for instance changes between communities, changes along a gradient,…) 
• Gamma diversity: diversity within a geographical area = sum alpha + beta.

On the temporal scale, biodiversity needs to be understood through geological and ecological windows.

Course

Biodiversity, the Tapestry of Life

La Biodiversité, la Fresque de la Vie

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