Factors that make Species Prone to Extinction
Small Population Size and Limited Distribution
 Especially true for island species – any change in habitat or a small dip in their
population can eliminate them.
 Widespread and common species are less likely to be wiped out.
o E.g. the slender-billed grackle, a bird which once occupied a single marsh
near Mexico City was driven to extinction.
 Species with small populations also tend to have low genetic diversity – inability to
adapt to changing conditions can prove fatal.
o Many large cat species are in this category – cheetah, snow leopard, and
tiger
Habitat Specialists
 organisms with a special diet or habitat requirements
 if their specific resource or habitat is put under threat so are they
 Some animals can only live on certain tree species
o E.g. the palila bird (a Hawaiian honeycreeper) is dependent on the mamane
tree for food and is losing habitat as these trees are cut down.
o E.g. giant panda which is dependent on bamboo
o E.g. koala which is dependent on eucalyptus
Low Reproductive Capacity
 Species that live for a long time tend to have a low reproductive rate making them
vulnerable to extinction
 A change in habitat or the introduction of a predator could cause a drop in population
leaving too few reproductive adults to support and maintain the population
 A slow reproductive rate means that any loss in numbers brings about a fast decline
o E.g. Steller’s sea cow was heavily hunted and unable to replace its numbers
fast enough
 Animals with long gestation times are also prone to low rates of reproduction and it
can take many years to recover population numbers.
o E.g. elephant: gestation time – 22 months
o E.g. rhino: gestation time – 16 months
 Some animals are only fertile for a small window of time
o E.g. giant panda: only fertile for 72 hours once a year
Poor Competitors
 Flightless and slow-moving birds are helpless under the pressures of hunting and
predation.
 Lack of mobility and poor defensive instincts make them sitting targets.
 Animals that evolved in the absence of predators are prone to extinction once a
predator (including man!) is introduced.
o E.g. the dodo on Mauritius had no predators and therefore did not need to fly
o E.g. other flightless birds: the great auk & the great elephant bird
Large Mammals
 Ready and significant source of meat
 Vulnerable to over-hunting
o E.g. whales hunted with harpoons
 Animals of large size also require large amounts of food and habitat
 If their habitat is reduced or fragmented, these animals find it difficult to find sufficient
food or space to survive.
 Most of the large mammals on earth are now endangered
o E.g. elephants, rhinoceros, many antelope species and the large cats
Valuable Products
 Wild animals and plants which have a value as food, pets, ceremonial objects or
marketable products are at risk from humans
o E.g. Animals valued as bush meat: monkeys, forest antelope, chimpanzees
and gorillas hunted for markets in west and central Africa
o E.g. many bird species with elaborate and colorful plumage are hunted for their
feathers: birds of paradise and the Huia bird of New Zealand.
o E.g. animals with products considered to be medicinal: rhinoceros horn
Altruistic Species
 Altruism is a selfless concern for the welfare of others.
 Some species have developed altruistic tendencies that helped preserve positive
bonds between animals and frightened off predators
o E.g. dodo, carrier pigeon, Carolina parakeet, and Steller’s sea cow
 When confronted with humans with guns, animals which come to the aid of hunted
mates are easily killed.
o E.g. wolves, gorillas, whales, elephants all refuse to leave their wounded
companions and are often killed themselves.
Clumping
 Species that require large numbers of their own kind for protection or to locate food
are vulnerable to extinction
o E.g. passenger pigeons could only survive amongst large numbers of their
own species, flocking and searching food sources
 When numbers in the flock are reduced, they split up and the separated populations
declined faster and became extinct
Position in Food Chain
 top predators are sensitive to any disturbance in the food chain and any reduction in
numbers of species at lower trophic levels can have disastrous consequences
 Also due to the 10% rule of energy loss through an ecosystem, large fierce animals
tend to be rare and are particularly sensitive to hunters and reductions in population
size
Irrespective of human interference any animal or plant which is rare has a restricted
distribution, a highly specialized habitat or niche, low reproductive potential or at the top of
the food chain is prone to extinction.