Maintaining Biodiversity

Have we overstated the tropical biodiversity crisis?William F. LauranceTrends in Ecology & EvolutionVol. 22: 65-70 February 2007

Extinction rates are likely to be higher in biodiversity hotspots

Fig 55.4

Terrestrial Biodiversity Hotspots

the 16 hotspots that sustain tropical forest have already lost, on average, 90% of their forest cover

Are we on the verge of a massive die-off of tropical species?

Changes in Extinctions and Diversity

Increased rural density leads to decreased forest.

This is because rural slash-and-burn farmers cause most forest loss.

The good news?

About 21–24% of species in the Asian tropics and 16–35% of species in the African tropics are threatened with possible extinction.

Rural populations are expected to decline.

Substantial areas of agricultural land are likely to be abandoned, because the population growth rates of many developing nations are slowing and because of increasing urbanization.

This could enable significant forest regeneration, which could help buffer species losses from deforestation.

Human vs Natural Disturbances

Rainforest clear cutting

Not all habitats are equal

A third to a half of all old-growth species avoid younger (<30-year-old) regrowth.

In many tropical regions, future pressures on forests will be determined more strongly by industrial drivers, globalization and macroeconomic forces than by local population density.

Rural populations are expected to decline, but increased urban population will demand more resources.

The precautionary principle maintains that one should err on the side of caution in conservation matters.

We need to evaluate critically the degree to which regenerating and degraded habitats, which are increasing dramatically at the expense of old-growth forests, can sustain tropical biodiversity

How many animals do we need to save?

How Many Animals Do We Want to Save? The Many Ways of Setting Population Target Levels for ConservationERIC W. SANDERSONNovember 2006 / Vol. 56 No. 11 BioScience 911

ExtinctionVortex

A population of a few individuals cannot survive

Can a number of individuals be set?

Can a number of individuals be set?

Fewest number of individuals for an area, but fewest number for what?

Can a number of individuals be set?

Extreme examples:

•Ecotourism want the largest possible population

•Mining or Agriculture would like none or somewhere else…NIMBY

What are the consequences of setting the wrong number?

What are the consequences of setting the wrong number?

•Too high

•Too low

Can a number of individuals be set?

•Scientists are reluctant to set a specific number

•Policymakers want information from scientists

What are the consequences of setting the wrong number?

Subjective values meets objective science

http://www.forwolves.org/ralph/historical.html

Yellowstone area wolf packs 2004

How many wolves should be in Yellowstone NP

How many tigers does the world need? None?

What criteria do we use to set limits?•Money•Land•Development

What criteria do we use to set limits?•Money•Land•Development

Who benefits?•Animals- what is the minimum number for sustainable survival

What criteria do we use to set limits?•Money•Land•Development

Who benefits?•Animals- what is the minimum number for sustainable survival•Ecosystem- What is the minimum number to maintain a healthy ecosystem?

What criteria do we use to set limits?•Money•Land•Development

Who benefits?•Animals- what is the minimum number for sustainable survival•Ecosystem- What is the minimum number to maintain a healthy ecosystem?•Humans- How many do we need to derive some beneifit?

Bonuses due... now