Lecture 23 summary

Lecture 23
Biodiversity II

There have been 5 mass extinctions in the earth’s history
We are presently going through the 6th mass extinction—this time brought on by human activities:

The spread of humans and their hunting activities
Conversion of habitat to agricultural production
The Industrial Revolution

6 major causes of biodiversity loss
ancient humans and their spread is associated with extinctions of large
animals on most continents—could be an interaction between
hunting, climate change, and community structure

commercial hunting—over fishing is major threat to ocean species

poaching is a major threat to vertebrate species—emptying of the forest,
people may rely on bushmeat for protein and income, often
associated with other practices such as logging

driven many species to extinction in the past and continues today

exotic species:
species that are introduced to an ecosystem, non-native, those that we are
concerned about are also invasive or nuisance

what is nuisance and what isn’t can often be culturally determined—bass vs. carp

Zebra mussels and Quagga mussels are taking nutrients out of the pelagic zone
and converting it to biomass in the benthic zone, change the foodweb and
impact the entire system

can greatly out-compete native species, extirpating them and possibly
driving them to extinction—Nile Perch in Lake Victoria

exotic species arrive by accident and on purpose
nostalgia for old world species
fisheries biologists introduce fish for culture
inter-basin transfers—species move around as hitchhikers on boats
sometimes as biocontrols which eventually get out of control

although many species may be successfully introduced to a new ecosystem, not all species become invasive, some common traits of successful invaders include:

*past history of successful invasions
*broad environmental tolerance
* thrive in human altered habitats
*native habitat is similar to exotic habitat
*have lots of progeny

habitat destruction:
habitat loss via destruction is important but so is habitat fragmentation, a
habitat needs to be large enough or ‘connected’ enough to support
viable populations

some species like disturbed habitats—some of these species may be
vectors of disease such as Lyme’s disease and deer and the white-
footed mouse

climate change:
may cause habitat alteration, northern habitats may become more like
present day southern habitats

southern species may be able to migrate north, but northern species will
have nowhere to go

many aspects are uncertain—will the whole community move together or will
species move at different rates or will some drop out?

may cause a breakdown of community interactions

protected areas will no longer protect the habitat it once protected and thus the
species it once protected

nothing was said about this topic in lecture but there are many examples of
pollution and loss of biodiversity such as dead zones, DDT and the
disappearance of bird species

domino effect:
the idea is that if one species becomes extinct others will follow

not a lot of evidence for domino effects

one example is the black footed ferret—uses prairie dog colonies
ferret is now rare because prairie dogs have been hunted and

likely not a very strong effect because of the complexity of ecosystems but
could maybe be more pronounced if keystone species is the one that

How do we know how many species are going extinct?
extinctions are now 1,000 to 10,000 times greater than background rates, this calculation
comes from:

estimating the species richness—about 2 million described species
number of unknown species is likely >10,000,000

estimate the rate of habitat loss—satellite data can tell us rate of deforestation,
land cover change

make predictions based on species-area relationships—as area declines species
number declines, increase area 10x means you increase species about 2x
example: Caribbean Islands and reptile diversity—an example of how
things might be as habitat destruction makes island fragments out
remaining native cover

Protecting Biodiversity
Two main areas: protected areas and the rest of the planet

Protected lands are increasing but are still only ~12% of earth’s terrestrial surface

That leaves 80-90% of land that must also be managed—delicate balance between protecting biodiversity and protecting human livelihoods
Need to manage the matrix!

Issues to consider in respect to protected areas:

Not all habitats are protected equally—where should we put more protected areas? we
shouldn’t protect lots of land but have no rain forests represented, grasslands are
highly under-represented because they are often the best agricultural lands

How do we design reserves: size, shape, connectivity

There’s a wide range of protected area categories: what are the goals, what are the
regulations, multiple use
Just because it’s protected doesn’t mean it’s strict protection—over 20% of
Michigan is protected but much of that land is multiple use—fishing,recreation,
hunting—how much biodiversity is really being protected in these lands?

If you pick good places, you can do a good job of protecting species of concern
ecosystem types
areas of high endemism

Use GIS to find gaps in protection—overlay map of current reserve network and map or
species occurrence and focus on the gaps

How big does a reserve have to be? Population size increases with land area—extinction
increases as land area decreases

Simple empirical relationships between components can tell you how big a reserve you
need for certain species—carnivores need much more area than herbivores

In Summary:

The sinister sextet accounts for most of the threats to biodiversity

Most important threat:
Habitat destruction
Invasive species
For the oceans and bushmeat—over-harvest is the most important
No real estimate for the effects of climate change—hard to predict how
species will migrate pole-ward and how successful they will be

Protecting biodiversity
*Protected areas cover ~12% of earth’s terrestrial surface so we also need to pay attention to the 80-90% that is not protected
*Protected areas have different management goals and these need to be taken in to consideration
*There are often gaps in the representation of different ecosystem types covered by protected areas
*Size, shape, and connectivity

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