Quantcast
Mongabay.com is considered a leading source of information on tropical forests by some of the world's top ecologists and conservationists. TROPICAL RAINFORESTS: Disappearing Opportunities

The Extinction Vortex



To clarify the concept of an extinction vortex, take a hypothetical example of a population ground-nesting jungle-fowl from Southeast Asia. Throughout their range, their native forests have been fragmented by logging and human development. Some fragments of forest are still large enough to support seemingly healthy, but small populations of jungle-fowl. In one location a population of 60 birds capable of reproduction, 30 females and 30 males, appears to be thriving. Every year an average hen successfully rears one chick that survives infancy, for a total of 30 new adult birds added to the population, while 30 birds (50% of the adult population) are consumed by predators or hunted by man.

Time Elapsed

Major Events Population

Initial

fragmentation

60

1 year

drought

42

2 years

flu

21

3 years

dogs

16

4 years

chance

8

5 years

 

5

:

 

 

11 years

 

3

12 years

 

2

13 years

 

0



The extinction vortex begins simply enough with an unusually long dry season. The drought takes its toll on the jungle-fowl population, especially the young. By the time monsoon rains begin, the population stands at 45: 20 females, 25 males. Over the course of the next year, the females have the same number of average young, one each, to give a total of 20. But 23 (about 50%) junglefowl are consumed in the course of the year leaving the population standing at 42: 17 females, 25 males.

At this time, peasants encouraged by a government settlement policy clear a patch of degraded forest land for subsistence agriculture. With them, the peasants bring livestock including chickens, closely related to jungle-fowl, and dogs. The chickens harbor an avarian flu, to which they are immune, which quickly spreads among the junglefowl population of the nearby forest fragment. The flu decimates the jungle-fowl; at year end 21 remain: 9 females, 12 males.

The presence of dogs increases predation of the jungle-fowl to 66% of the adult population every year so after another year the population stands at just 16: 6 females, 10 males.

The population of females is steadily declining either coincidently or perhaps because females are not as agile as males in escaping predators. In any case, demographic stochasticity spells the beginning of the end for the jungle-fowl. It might be the impact of the dogs disturbing nest sites or maybe just a stroke of bad luck for the jungle-fowl: only 3 females reproduce in the next year. By the end of the year the population is down to 8; 2 females, 6 males.

Now it is probably only a matter of time before the species goes extinct in the forest fragment. With the presence of dogs, the death rate of the jungle-fowl exceeds their birthrate. By the end of 5 years the population is down to 5: 2 females, 3 males. As the population density is low, predation rates by dogs drop slightly and the adult population of birds fluctuates between 4 and 8 for the next several years. However the species is on the brink of disappearing. All it takes now is one chance event.

The end comes quite rapidly. The population dips to 3, and the single remaining adult female is crushed by a tree limb that falls during a thunderstorm. Neither of her three chicks survive without her protection. The two male birds wander the forest looking for the mate they will never find. After the final male jungle-fowl is eaten by a python, the species is extinct from the forest patch.

The final death of the jungle-fowl of the Asian forest patch is not primarily responsible for the extinction of the species. The extinction of the jungle-fowl was made possible by its isolation. The small population became more susceptible to chance events that further reduced its size and made it more susceptible other factors.



Continued: Extinction


Other pages in this section:

Consequences of Deforestation
Erosion
Loss of Renewable Resources
Atmospheric Role
- - - - -
References
References
References
References
References
Local Climate Regulation
Loss of Species, Disease
Climactic Role
Extinction
- - - - -
Kids version of this section
- Why are rainforests important?
- Climate
- Home to wildlife
- Water cycle
- Erosion control
- Extinction


Selection of information sources








For kids

Tour: the Amazon

Rainforest news

Tour: Indonesia's rainforests

 Home
 What's New
 About
 Rainforests
   Mission
   Introduction
   Characteristics
   Biodiversity
   The Canopy
   Forest Floor
   Forest Waters
   Indigenous People
   Deforestation
   Consequences
   Saving Rainforests
   Amazon
   Borneo
   Congo
   New Guinea
   Sulawesi
   REDD
   Country Profiles
   Statistics
   Works Cited
   For Kids
   For Teachers
   Photos/Images
   Expert Interviews
   Rainforest News
  Forest data
   Forest loss tracker
   Global deforestation
   Tropical deforestation
   By country
   Deforestation charts
   Regional forest data
   Deforestation drivers
 XML Feeds
 Pictures
 Books
 Education
 Newsletter
 Contact

Nature Blog Network



 CONTENTS
Rainforests
Tropical Fish
News
Madagascar
Pictures
Kids' Site
Languages
TCS Journal
About
Archives
Topics | RSS
Newsletter




 Other languages
Arabic
Bengali
Chinese (CN) (expanded)
Chinese (TW)
Croatian
Danish
Dutch
Farsi
French (expanded)
German (expanded)
Greek
Hindi
Hungarian
Indonesian
Italian
Japanese (expanded)
Javanese
Korean
Malagasy
Malay
Marathi
Norwegian
Polish
Portuguese (expanded)
Russian
Slovak
Spanish (expanded)
Swahili
Swedish
Ukrainian



 WEEKLY NEWSLETTER
 Email:


 INTERACT
Facebook
Twitter
Contact
Help
Photo store
Mongabay gear




what's new | rainforests home | for kids | help | madagascar | search | about | languages | contact

Copyright Rhett Butler 1994-2015

Carbon dioxide (CO2) emissions generated from mongabay.com operations (server, data transfer, travel) are mitigated through an association with Anthrotect,
an organization working with Afro-indigenous and Embera communities to protect forests in Colombia's Darien region.
Anthrotect is protecting the habitat of mongabay's mascot: the scale-crested pygmy tyrant.

"Rainforest" is used interchangeably with "rain forest" on this site. "Jungle" is generally not used.