Biodiversity - Week 6

Hotspots are areas with high densities of biodiversity that are significantly threatened by human impacts. The biodiversity component is generally measured in species richness, though sometimes numbers of endemic or rare species are used. Hotspots are hot due to their anthropogenic and biogeographic histories. Species richness is highest in the tropics where the habitat is highly varied because it was not glaciated. Endemic species are found mainly in archipelagos, areas with a wide range of altitudes, and narrow annual temperature ranges where there is high allopatric specieation. Threatened species are found in areas of high human impact. Areas of high human impact tend to coincide with those of high diversity. Hotspots seem to provide an opportunity to support the most species at the lowest cost. By saving the 25 hotspots list in Myers et. al. 2000 44% of species of vascular plants and 35% of species in four vertebrate groups would be conserved in 1.4% of the land surface. Myers hotspots are areas of high species richness and have lost 70% of its primary vegetation.

There are shortcomings in the hotspot theory for conservation. Hotspots don’t measure ecosystem functioning or species other than vascular plants and don’t take into account the intrinsic value of nature, provide for the needs of larger animals, and are all areas of high human impact. Areas that have already lost 70% of the primary vegetation are likely to have an extinction debt. These areas may currently appear stable but actual contain a large number of the relic and ghost species brought up in The End of the Wild. The Ceballos and Ehrlich article looks at the congruence of hotspots measures of species richness, endemism, and endangerment for nomarine mammals. They found that these measures were noncongruent with only 1% of cells and 16% of speices common to all three types of mammalian hotspots. They found that using complementarity represents the maximum number of species in the minimum number of cells. Kareiva and Marvier add that perhaps focus should be placed on maintaining functioning ecosystems throughout the world, not only in the tropics, especially as this may add variety to plant and animal species lineages for future evolutionary breakthroughs. They propose, additionally, a performance based system for determining areas of conservation rather than species lists.

In class we examined factors that should be considered when determining where to focus conservation efforts.

Suggestions from the readings and the class include sites….

With high endemism

That are species rich

With rare or endangered species

With high and varied ecosystem services

With high ecosystem function

That are highly sensitive to species loss

That are future areas of threat (as opposed to those already in crisis)

That can be used to give people experiences achieved through diversity

With high beta diversity

In cost effective areas

With the greatest potential to produce novelty (evolutionary potential)

That are resilient and/or stable in the face of environmental change

There are many factors to consider when deciding what areas to conserve. One additional consideration is using a performance based conservation plan, rather than one relying on species lists. While the authors of this weeks articles and the students and professors of the Ecology Seminar disagree on what to conserve and how to conserve it, there is a common message that biodiversity is threatened and action in the form of research and conservation must be taken.