Saving Species

What does it take to save rare species from extinction?

Extinction Rates

• The Sixth Mass Extinction:– Current extinction rates are 100 times greater

than background– Previous mass extinction rates were between

about 5-10 times greater than background– Background rate: 1-2 species per year– Modern rate: 3 species per hour!

Risks to rare species

• We know about the “extinction vortex” and the many threats faced by rare species

• If we agree that at least some of these rare species should be saved – it is our responsibility to try to do so – then…– We must protect populations in order to save species

Population Size

• How big must a population be to be “save-able?”

• “Minimum Viable Population” (MVP) analysis– Definition: The smallest population size that

can be predicted to have a very high chance (e.g. 99%) of persisting into the foreseeable future (e.g. 1000 yrs)

Desert Bighorn Sheep

Figure 3.1 in Primack – How big do populations of Bighorns need to be for long-term survival?

(figure from Berger 1990)

Habitat Size

• How big must the habitat area available be in order for a population to survive?

• “Minimum Dynamic Area” (MDA)– This will depend very much on the size of the

species and its territorial restrictions

African Lions

• Large carnivores, such as lions, need huge areas to support viable populations

• Reserves of 10,000 km2 needed!

• To support small mammals in Africa, reserves of 100-1000 km2 necessary

Multiple Ways to Preserve Rare or Endangered Species

• What approaches can you think of that might be necessary under different conditions?

• Retain or improve habitat (remove threats) – for some species this is enough

• Captive breeding with reintroduction into good habitat

• Off-site conservation

Habitat Improvement or Preservation

• For some species, it is enough to simply remove an external threat that was driving population sizes down

• If the habitat is relatively intact, once the threat is removed the species will recover

Bald Eagle

http://www.npca.org/wildlife_protection/wildlife_facts/baldeagle.html

Threat: DDT

The Great Whales

Threat: Over-hunting

Habitat Improvement or Preservation

• For other species, the main threat to their existence may be habitat loss or fragmentation

• Creating habitat reserves may be a successful way to help the species recover and maintain viable population sizes

• …but this is not always easy… (more on this topic next week); and it’s easier for the “charismatic mega-fauna” than for other species

African Elephant

Fig. 3.8 in Primack – What habitat area appears to be necessary for long-term survival in this species?

Hawaiian Monk Seal

Primack Fig. 3.7 - What human impact was removed to improve Monk Seal habitat?

Northern Spotted Owl

A famous example of how hard it can be to set aside habitat for the preservation of a species…

Captive Breeding for Reintroduction to the Wild

• In some cases, populations have been driven so low that there is no hope of a species surviving without human intervention (Wilson’s “100 Heartbeats Club”)

• Several examples of successful captive breeding programs

• BUT this can only work if measures have been taken to insure that the habitat is preserved or restored in preparation for re-release– Sometimes controversial

Peregrine Falcon

A famous success story – initial threat: DDT; Habitat: abundant!

California Condor

http://www.fws.gov/hoppermountain/cacondor/condormanagement.html

Population declined in wild to 22 individuals; after captive breeding now up to 289. Visit the site linked below…

Whooping Crane

Video clip…

Yellowstone Wolves

Often a species that is threatened in one part of its range can be reintroduced from another part of the range where it is still abundant.

Off-Site Conservation

• Some species have declined to such low population levels, and they or their habitat are so threatened in the wild that the only way to preserve them is in captivity

• The species can be maintained in zoos, aquaria, botanical gardens, seed banks…

• Very expensive – only done as a last resort• Risk: may lose habitat in the meantime; for

some, they will never be reintroduced…

Przewalski’s Horse

The last takhi seen in the Gobi region was in the 1960s. The 1,200 some horses alive today are descendents of 12 individuals captured and bred in zoos.