Global Biodiversity

We examine biodiversity at several levels. It has evolutionary and ecological aspects.

Populations of species sometimes include distinguishable subspecies with nonoverlapping geographic ranges. Subspecies typically differ morphologically or behaviorally. There may be many subspecies. Some people recognize 30 subspecies of cougars. There are 31 subspecies of the house sparrow. Often unclear just what constitutes a subspecies.

Evolutionarily Significant Unit: a geographically isolated portion of the species population that also has a high level of genetic difference from other subpopulations of the species, whether or not this difference is recognized taxonomically. The black sea turtle Chelonia mydas agassizii ?

Of particular interest are endemic taxa. Restricted to a particular region. One aspect of biodiversity that we are concerned with is the degree of endemicity of the biota of a region. If a region has high endemicity, then it has many taxa that are found nowhere else. Areas with high endemicity include oceanic islands, freshwater lakes in rift basins, and land areas bounded by mountain ranges.

Some long-isolated areas have particularly high levels of endemicity. Animal Info - Madagascar

Lemurs

Madagascar’s fossa

The Galapagos Islands

Marine iguana Galapagos tortoise Flightless cormorant

Darwin’s Finches

What is a species? Several concepts: Biological species – a group of actually or potentially interbreeding individuals that are reproductively isolated from other such groups. Phylogenetic species – a group of individuals that is distinct in its characteristics and has a common ancestry.

Application of the phylogenetic species concept will likely increase the number of recognized species, with some current some subspecies being elevated to species status.

So, how many species are there? Around 1.5 million described. Many more undescribed. How many remains in doubt. As many estimates as there are biologists. Terry Erwin fogged trees in the canopy of tropical forests. From 19 trees belonging to one species, he found 1,200 species of beetles. He estimated 162 to be restricted to that tree species. Through a series of extrapolations, he estimated that there were some 30,000,000 species of organisms on earth.

Biodiversity hotspots

Russia’s Lake Baikal

Nerpa

Baikal lake Web World - Ichthyofauna of Baikal lake Omul Golomyanka

African Rift Lakes Lake Malawi

There are at least 280 cichlids in Lake Malawi, perhaps as many as The Cichlid Fishes of Lake Malawi, Africa

California’s Vernal Pools

VernalPools.Org - California Vernal Pools

In addition to biodiversity hotspots, we can see some global trends in biodiversity: Diversity tends to be higher in the tropics than at higher latitudes. Why? In terrestrial habitats, diversity tends to be higher in mountainous regions. Why? In marine habitats, diversity tends to be higher in systems like coral reefs or mangrove swamps. Why?

There is also great variation above the species level. The variety of interactions leads to a great number of ecosystems. However, there’s not really a good way of recognizing distinct ecosystems. It’s probably pretty much continuous.

We do, however, need a way of designating ecosystems for conservation purposes. Several have been developed. Bailey developed a hierarchical system: Domains Divisions Provinces Baileys' Eco-Regions (July 1995)

Udvardy developed a classification of biogeographic provinces based on 14 major land and fw biomes and 8 biogeographic realms. Biomes are ecosystem types defined by dominant plant life forms, biogeographic realms correspond to major continental units. Altogether, his system identifies 193 biogeographic provinces. This has become the basis for global conservation planning. Udvardy's biogeographic regions

Measures of Diversity alpha diversity –describe (richness and evenness) beta diversity – degree of change in species from one community type to another. Changes from region to region. gamma diversity – for a region as a whole, the overall richness in species reflects the number of community types present, the alpha diversity of each, and the pattern of beta diversity (change) from one type to the next type.

Formula for one index of alpha diversity (Shannon Index)

What determines diversity? Who knows. Some ideas… Time Stability Productivity Habitat heterogeneity Predation, competition, etc.

Joe Connell developed the intermediate disturbance hypothesis.

Catastrophism hypothesis. How long has it been since the last catastrophe?