REG-32806 Summary
Week 1 - Monday
Three types of biodiversity
- Genetic
- Species
- Ecosystem
Diversity equals stability. For example, if
you have a monoculture of pine trees and a
mountain pine beetle, than if a plague
happens, all the trees are likely to die. This
can have disastrous consequences for the
ecosystem. If there were more tree species,
than at least part of the forest might survive
and grow back more easily, increasing
stability.
Causes for species extinction
- Anthropogenic factors
o Poaching
o Farming
o Pollution
o
- Invasive species
- Diseases
- Habitat loss
- Climate change
Current extinction rates
• 25% of mammals, 13%
of birds, >21 000 plants
& other organisms
• Similar rate as other 5
global mass-extinctions
,Week 1 – Tuesday [OVEREXPLOITATION]
Overexploitation of resources is on of the main threats to biodiversity. A famous example is
the exploitation of American Bison. In the 19th century people thought that there were so
many bison that they could easily hunt them by the millions for their meat and their skin.
Within 30 years their populations dropped from 30 million to about 100 animals. This was
literally an extermination.
One of the demands was the bison hide. In 1870 they invented an industrial method
for tanning buffalo hides. They needed leather belts for the machinery, thus bison hides were
used. The shoes of military were made of bison hides. In the 1870s the Sioux were defeated.
They longly resisted the expansion of white colonists, but after their defeat the colonists could
easily travel through the country, also because of the extension of the northern pacific
railroad. The few bisons that remaind were preserved and are now bred to increase their
population.
This near extermination of bison eventually led to the rise of conservation movements in
America and the development of national park systems.
Tragedy of the commons. is a situation in a shared-resource system where individual users, acting
independently according to their own self-interest, behave contrary to the common good of all
users by depleting or spoiling the shared resource through their collective action.
- Incompletely defined and enforced property rights
- Users do not consider social benefits and costs
- Benefits are for individual, negative effects for all
- Harmful effects on third parties (depletion of wildlife)
,Overexploitation happens in many parts of the world and the underlying problem is that often
it is thought that natural resources are almost indepletable. For example the oceans seem so
vast and full of fish that the fishery industry is booming and regulations on fishing are
insufficient.
- Fishing
- Hunting and poaching (for meat, ornaments, medicinal purposes)
o The relationship between fishing and bushmeat hunting is that in many coastal
countries where the oceans have been depleted of fish, people turn to
bushmeat (bushmeat is a general term for meat originated from wild animals)
to suffice in the food demand
- Forest loss (is different from exploitation, as the forest is removed rather than ‘used’)
o For timber, fuelwood, charcoal, room for agriculture or livestock
It is noticable that with the ‘colonisation’ of
continents by early humans, the number of
large mammal species that went extinct
increased significantly.
Theory 1: Humans originated in Africa and
migrated to different parts of the world and
subsequently started hunting the local
fauna, leading to the extinction of many
species.
Theory 2: Because of climate change,
migration of humans to different parts of
the world was facilitated through newly
formed land bridges and changing
environmental conditions. This coincided
with the impact of these environmental
,factors on animal species that might have played a role in their extinction.
The number of species threatened is highest in
developing countries. This has multiple reasons: the
demand for alternative foodsources from the wild is
higher in countries that have little access to sustainable
agriculture. Also, there is high demand from western
culture for luxury products that originate from wildlife
in developing countries, this facilitates illegal wildlife
hunting by poachers that need to make a living.
Developed countries e.g. Europe, America, etc. already
have exterminated many species in the far past, there
used to be thousands of species that have gone extinct
when western countries started to develop.
Hunting threat to species is proportional to body size. Interestingly, the largest proportion (in
terms of biomass) is the small animals with a body weight between 0.1 and 10kg. But if we
look at the percentage of actual species threatened by hunting practices, it’s the large
mammals that are under severe pressure. This has to do with the large number of small
species compared to the relatively limited number of megafauna species: lot of small species
like rodents, bats, e.g. but only few large species like rhino, giraffe, antilope.
, Pet trade also puts a huge threat to wildlife, particularly bird species are popular pets. Parrots
most threatened by pet trade.
The spatial effect of wild animal hunting is clear
form these graphs. The X-axis shows the travel
time / distance from the access point of a hunter.
The further away from the ‘hunting-grounds’ of a
hunter, the more species can be found. The
closer to the hunting grounds, the lower the
abundance of wild animals.
Calculations have been made and this correlates
to a total of 33% of brazilian rainforest affected
by hunters.
A large factor that contributes to the extent of
wildlife hunting is supply, demand and prices. In
places where poultry farming is high the prices
for poultry are low (large supply). In places where
poultry is not supplied on a large scale, the prices
are higher and therefore local people might shift
to bushmeat as a means to suffice in demand and
keep it financially profitable.
In short, people in the city eat chicken because
it’s cheap. People near forest eat bushmeat
because poultry is too expensive.
Cascading ecosystem effects of hunting:
LARGE PREDATORS
- Loss of predators due to prey depletion
- Loss of top-down control by large
predators to keep ecosystem healthy
- Ecological release of small mammals
- Less seed dispersal (more food abundant
for rodent species) resulting in increased rodent populations
SMALL MAMMALS
- Less consumption of vegetation and invertebrates
- Less soil disturbance
- Prey depletion
