The State of Things

A recent study (Junker et al., 2012) has detailed recent decline in suitable environmental conditions for African great apes.  As I have discussed in the past, habitat loss is a serious challenge that may lead the extinction of the great apes.  However, this study has shown conclusively that habitat loss is a larger problem than previously believed and is causing great ape populations to collapse at a faster rate than previously predicted.

Pan-African data

The three species of African great ape (i.e., chimpanzees, gorillas and bonobos) have suffered disproportionately from the affects of habitat loss, and certain geographical regions of Africa have seen greater habitat loss and faster great ape population decline than others.

Gorillas have been hit the hardest.  Since 1995 cross river gorillas have lost 59% of their habitat, eastern gorillas have lost 52% of their habitat and western gorillas have lost 31% of their habitat.  These data reveal that for gorillas, continental location seems to mean very little.  Whether in the east (52%) or west (59% and 31%) of Africa, habitat loss has been incredibly disastrous and rapid.

However, there is significant variation between the effects of this habitat loss on overall subspecies population totals.  Although all subspecies have suffered massive population decline (about half since the 1980s), two of the four subspecies may be on the verge of extinction.  There are currently 95,000 and 5,000 western lowland and eastern lowland gorillas respectively.  These totals are low enough to warrant an “endangered” status from the IUCN.  However, there are only 700 and 300 mountain and cross river gorillas remaining in the wild, which has caused several conservationists to believe they are beyond saving.

The reasons for the disproportionate population decline seems to be because both of these subspecies only live in mountain environments.  This increases the likelihood that their populations would be isolated and fragmented as a result of habitat loss.  For subspecies with such low total populations, genetic isolation due to fragmentation could cause genetic bottleneck too small to survive.  Even the most optimistic researchers have found it hard to argue against the likelihood that they will not be extant in 2020.

For bonobos and chimpanzees the data does not paint as bleak a picture, but still quantifies the plight of species struggling to deal with our increased presence.  Bonobos have suffered a 29% reduction in habitat and chimpanzees have suffered in between 11-17% reduction in habitat over the past 20 years.  The toll on overall population size has been shocking.  There are fewer than 50,000 bonobos and approximately 250,000 chimpanzees remaining in the wild.  This may not seem as bad as gorilla population decline, but it is important to remember that in the 1960s there were close to 2 million chimpanzees.

Although both chimpanzees and bonobos are more ecologically flexible than gorillas, habitat loss still poses extreme challenges to their continued existence.  Less habitat means less resources, increased fragmentation, more contact with humans (which increases the likelihood of zoonotic disease transmission) and less space to hide from poachers.  In essence, habitat loss compounds other problems that are causing chimpanzee and bonobo population to collapse at alarming rates.  In some areas of Africa populations have collapsed by more than 90% due to human-contracted disease (e.g., Ebolavirus) and increased hunting.

These data reveal more clearly than ever that great ape protected area establishment and proper management are more important than ever.  If we don’t act soon, we may be the only member of the Hominidae family remaining by 2100.

References

Junker et al., 2012.  Recent decline in suitable environmental conditions for African great apes.  Diversity and Distributions, 18: 1077-1091.

 

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About Cadell Last
Hello. I'm probably drinking coffee and reading.

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