1) Prairie dogs and pocket gophers disturb soil and vegetation through their burrowing and herbivory activities. This intermediate disturbance creates patchy plant communities with varying levels of grasses, forbs, and shrubs. 2) Species diversity is greatest at intermediate levels of disturbance. Too much or too little disturbance favors either colonizing species or stronger competitors, respectively. 3) While urbanization threatens biodiversity through habitat loss and simplification, some studies find that urban areas can still support significant diversity, depending on the taxonomic group. Bird diversity specifically may peak at intermediate levels of urban land use.

3. The Lotka-Volterra
competition equations
predict that under such
circumstances, one
species will exclude all
others.
Species coexist when intraspecific competition
is stronger than interspecific competition.

4. interspecific
competition
intraspecific
competition
(Competition between individuals of two species
that reduces the fitness of both.)
Species coexist
(Competition with members of their own species.)

5. However, as Sousa’s work shows,
even where species compete for a
single resource, such as space in the
intertidal zone, several species may
coexist if disturbance prevents
competitive exclusion

12. Weigh
approximately 1
kg as adults
Live in colonies containing 10-55 individuals
per hectare

13.  Build extensive burrow systems that are 1 to 3 m deep
and about 15 m long, with tunnel diameters of 10
to 13 cm and two entrances

15. have
substantial effects on the
structure of plant communities
at several spatial scales

17. Because of the activities of these rodents, each of
these areas supports vegetative communities
distinctive from the surrounding
landscape. Within a colony, prairie dog activities
create patchiness on a smaller scale, with areas
of forbs and shrubs, grass and forbs, and grass
within the surrounding matrix of prairie
grassland.

18. Whicker and Detling
estimate that plant
species diversity is
greatest in areas
experiencing
intermediate levels of
disturbance by prairie
dogs

20. By burrowing and piling earth and by
grazing and clipping vegetation, prairie
dogs remove vegetation from areas around
their burrows. These bare patches are then
open for colonization by plants. However,
some plant species are more likely to
colonize these open patches.

21. Those species investing most heavily in dispersal are
usually the first to arrive. However, these early colonists
can be displaced by better competitors that arrive later.
The persistence of both good colonizers and good
competitors in a plant community depends upon
intermediate levels of disturbance. Too much
disturbance and the community is dominated by the
good colonizers; too little disturbance and the better
competitors dominate.

22. One of the most important of these are the pocket
gophers of the family Geomyidae.

26. The influences of prairie
dogs and pocket gophers
on plant communities are a
consequence of a
combination of physical
disturbances due to
burrowing and to feeding,
since both are herbivores.

29. Housing
developments cover
the countryside as
human populations
continue their rapid
growth.

30. Deforestation
continues at an
alarming rate in both
temperate and tropical
regions.

31. Industries
pollute air and
water

32. The destruction of natural
communities that we often
associate with humans is a
consequence of the extreme levels
of disturbance of which our species
is capable

33. Figure 16.22

34. Figure 16.22
Human populations and activity are a major
source of disturbance. For example:
(a). Housing developments generally simplify natural
ecosystems and feed demand for natural resources
such as (b) the wood harvested from this clear-cut
forest and (c) the coal from this mountaintop which is
mined to supply electrical power to human populations

35. The growing energy demands of our population and our
reliance on fossil fuels are driving global warming,
disturbing habitats far beyond human centers. For example:
(d) By melting Arctic sea ice, which is prime hunting habitat
for polar bears

36. These are the high levels of disturbance that
the intermediate disturbance hypothesis
predicts will lead to reduced diversity. Not
surprisingly, human disturbance threatens
thousands of species extinction

37. Environments disturbed by human activity are
not, however devoid of life and some, such as
the chalk grasslands of Europe, support higher
diversity under traditional management. Even
Urban environments can support surprising
levels of diversity

38. Chalk Grasslands of Europe

40. While Urbanization is considered a major
threat to biodiversity, Stuart Pickett, Director
of the Baltimore Ecosystem Study Long Term
Ecological Research (LTER) Program, points
out that ongoing studies are revealing that the
urban biota is diverse, often much more so than
commonly thought.

41. Studies of Urban Diversity have
included plants, land snails, beetles,
butterflies, spiders, fish, aquatic
invertebrates, mammals, and one of he
most studied group of organisms: birds

43. Urbanization has been shown to reduce both bird
species richness and evenness in Phoenix,
Arizona, and Baltimore, Maryland, an effect
observed in many other urban settings.
It turns out, however, that landscapes exposed to
some degree of human land use can support
substantial levels of bird diversity.

44. In the study of bird species richness along
gradients of land use intensity, Robert Blair
(2004) recorded the highest number of bird
species in areas of intermediate use in both
Northern California and South Western Ohio.

45. Figure 16.23a

46. Figure 16.23a
Shows that bird species richness peaked
in the middle of gradients of land use
intensity, peaking in both study areas in
golf courses

47. One of the drivers of change in bird species richness
along these gradients, is habitat modification.
Habitat changes from the nature preserve to the
business district along these gradients included
decreases in tree and shrub cover and increases in
coverage by pavement and buildings.

48. Most significantly, the richness of native woodland birds
decreased as land use intensity increased in both California
and Ohio.
As bird species associated with natural woodland
vegetation declined in representation along the
gradients, they were replaced by other, generally
more widespread species, such as nonn- native
house sparrows, Passer domesticus, and starlings,
Sturnus vulgarus.

49. As a result, the similarity between the bird
communities at the California and Ohio
study sites increased toward the Urban core
of the study gradients, where widespread,
generalist species were most common

50. Figure 16.24

51. This pattern gives some insight into the basis
for concerns that an increasingly urbanized
world will contribute to a homogenized global
biota---- that is, urbanization will reduce
regional differences in biodiversity.

52. Pickett and his colleagues (2008) counter this concern by
pointing out that the diversity of other groups of organisms
For example: ground beetles and plants, do not seem to
be affected by urbanization. The exponential growth in
studies of urban ecology will likely soon produce the
information needed to address these differences, and
perhaps remedy remaining concerns about the ecological
urbanization.

53. #GODBLESS 