Urbanization, Biodiversity, and Conrvation
Author(s): MICHAEL L. McKINNEY
Source: BioScience, 52(10):883-890. 2002.
Published By: American Institute of Biological Sciences
DOI: 10.1641/0006-3568(2002)052[0883:UBAC]2.0.CO;2
URL:
www.bioone/doi/full/10.1641/0006-
生物医学工程考研
3568%282002%29052%5B0883%3AUBAC%5D2.0.CO%3B2
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Articles
A mong the many human activities that cau
habitat loss (Czech et al.2000),urban development
produces some of the greatest local extinction rates and fre-
quently eliminates the large majority of native species (Vale
and Vale 1976,Luniak 1994,Kowarik 1995,Marzluff2001).
济南市七里山幼儿园Also,urbanization is often more lasting than other types of
habitat loss.Throughout much of New England,for exam-
ple,ecological succession is restoring forest habitat lost from
farming and logging,whereas most urbanized areas in that
region not only persist but continue to expand and threaten
初中生课外辅导other local ecosystems (Stein et al.2000).
Another great conrvation challenge of urban growth is
that it replaces the native species that are lost with wide-
spread “weedy”nonnative species.This replacement consti-tutes the process of biotic homogenization that threatens to reduce the biological uniqueness of local ecosystems (Blair 2001).Urban-gradient studies show that,for many taxa,for example,plants (Kowarik 1995) and birds and butterflies (Blair and Launer 1997),the number of nonnative species in-creas toward centers of urbanization,while the number of native species decreas.
The final conrvation challenge of sprawl is its current and growing geographical extent (Benfield et al.1999).A review by Czech and colleagues (2000) finds that urbanization en-dangers more species and is more geographically ubiquitous in the mainland United States than any other human activ-ity.Species threatened by urbanization also tend to be threat-ened by agriculture,recreation,roads,and many other human impacts,emphasizing the uniquely far-reaching transfor-mations that accompany urban sprawl.
About 50% of the US population lives in the suburbs, with another 30% living in cities (USCB 2001).Over 5% of the total surface area of the United States is covered by urban and other built-up areas (USCB 2001).This is more land than is covered by the combined total of national and state parks and areas prerved by the Nature Conrvancy.More omi-nously,the growth rate of urban land u is accelerating faster than land prerved as parks or conrvation areas by the Conrvancy (figure 1).Much of this growth is from the spread of suburban housing.It is estimated,for example, that residential yards occupy 135,000 acres in the state of Missouri (MDC 2002).This residential landscape reprents nearly 1% of the total area of Missouri and is nearly three times the area occupied by Missouri state parks.
Here I review the growing literature that documents how urban (and suburban) expansion harms nati
ve ecosystems. This knowledge can aid conrvation efforts in two major ways.One is through the u of ecological principles—such as prerving remnant natural habitat and restoring modified habitats to promote native species conrvation—to reduce the impacts of urbanization on native ecosystems.Rare and endangered species sometimes occur in urbanized habitats (Kendle and Forbes 1997,Godefroid 2001) and thus could be conrved there.Managing the large amount of residential veg-etation (1% of the state area,as noted above) in ways that pro-mote native plants and animals could also make a significant
contribution to conrvation.
Urbanization,Biodiversity, and Conrvation
MICHAEL L. M C KINNEY
T HE IMPACTS OF URBANIZATION ON
NATIVE SPECIES ARE POORLY STUDIED,
BUT EDUCATING A HIGHLY URBANIZED
HUMAN POPULATION ABOUT THESE
IMPACTS CAN GREATLY IMPROVE SPECIES
utilization
CONSERV ATION IN ALL ECOSYSTEMS
October 2002 / Vol.52 No.10• BioScience883
884BioScience • October 2002 / Vol.52 No.10
Articles英国留学申请费
A cond way in which the study of urban ecology can rve
conrvation is by helping to develop a more ecologically
informed public.Providing a well-informed public could be
the most important application of urban ecology,as a means
of promoting effective conrvation of native species (Kendle
and Forbes 1997).Becau 80% of the American public lives in or near urban areas,there are many opportunities for cre-ating an informed public that can wield enormous economic and political pressure to promote conrvation policies.Peo-ple who live in urban environments often have a great ap-preciation of many urban species,such as birds (Clergeau et al.2001).Indeed,residents of suburban and urban areas tend to place a much higher value on species conrvation than tho living in rural areas (Kellert 1996).This is reflected in voting behavior:Legislators from highly urbanized states and districts tend to be more supportive of strengthening the Endangered Species Act (Mehmood and Zhang 2001).Unfortunately,the conrvation opportunities are hin-dered by the very poor ecological knowledge of typical Amer-ican urbanites.A survey of T exas high school students,for ex-ample,showed that 60% of the students misidentified the opossum as a rodent and that ecological understanding of hu-man effects on biota was even poorer;only 2% of the students knew that raccoons tend to benefit from many human ac-tivities (Adams et al.1987).
The urban–rural gradient: General patterns
Urban-to-rural gradient studies examine changes in plants and animals along a tranct from the inner city to surrounding,less-altered ecosystems;they also show what happens to sur-rounding native ecosystems as ur-ban sprawl expands.General pat-terns that emerge from the stud-ies are described below.
Physical gradients.Physical
changes along the gradient strongly influence available habi-tat for native species.A number of reviews (Sukopp and W erner 1982,Medley et al.1995,Pickett et al.2001) show increas in the physical changes,as one moves to-ward the urban core,in such met-rics as human population density,road density,air and soil pollu-tion,average ambient tempera-ture (“heat island”effect),aver-age annual rainfall,soil compaction,soil alkalinity,and other indicators of anthropogenic disturbance.The percentage of area that is impervious surface (pavement,asphalt,buildings)ranges from well over 50% at the
urban core to less than 20% at the fringe of urban expansion (figure 2).In addition,the amount of subsidized energy and matter imported for u by humans and available to other species increas toward the urban center (Collins et al.2000,Pickett et al.2001).Habitat-loss gradient.The physical changes produce
a gradient of natural habitat loss that steepens from rural ar-eas toward the urban center.As habitat is lost,it becomes in-creasingly fragmented into more numerous but smaller remnant patches (Medley et al.1995,Collins et al.2000).The lost natural habitat is then replaced by four types of altered habitat that become progressively more common toward the urban core.The four types of replacement habitat are listed below,in order of increasing habitability to most native species and decreasing proportion of coverage toward the urban core.The latter three types are bad on Whitney (1985).
1.Built habitat:buildings and aled surfaces,such as
roads 2.Managed vegetation:residential,commercial,and other regularly maintained green spaces
3.Ruderal vegetation:empty lots,abandoned farmland,and other green space that is cleared but not managed
4.Natural remnant vegetation:remaining islands of origi-nal vegetation (usually subject to substantial nonnative plant invasion)
Figure 1.Amount of land covered in the lower 48 states,by category.Source: All data are
from Statistical Abstract of the United States for the years shown,except for Nature Con-rvancy data,which is from Stein and colleagues (2000).
磅礴的拼音
A c r e s (m i l l i o n s )
Diversity changes along the
urban–rural gradient
我是冠军英文It is probably intuitive to even the most casual obrver that the increasing fragmentation of natural habitat by human disturbances in the direction toward urban centers will tend to reduce species rich-ness (number of species) in that direction.There are,how-ever,many variables that can affect the rate and consistency of species loss along the gra-dient,so empirical studies are crucial in measuring urban impacts.
ugt
Urban core,low diver-sity.Many studies document that the lowest species diver-sities along the urban–rural gradient occur in the inten-sively “built”environments of
the urban core.This has been shown for many taxa,includ-ing plants (Kowarik 1995),birds and butterflies (Blair 2001), many incts (Denys and Schmidt 1998,McIntyre 2000), and mammals (Mac
kin-Rogalska et al.1988).In all the taxa,the number of species at the urban core is reduced to less than half of that found in the rural,more natural areas at the opposite end of the gradient (figure 2).
Blair (2001),for example,found just 7 summer resident bird species in the central business district of Palo Alto,Califor-nia,compared with 21 species that inhabited a natural area (prerve) outside the city limits.Similar reductions were found for birds and butterflies in other cities,as shown by Blair’s (2001),and especially by Marzluff’s (2001),compre-hensive compilation of studies on urbanization impacts on birds.
Much of the reduction in richness is obviously caud by the loss of vegetation.The number of species of animal taxa, such as birds (Shugart et al.1975) and incts (Majer 1997), tends to correlate with the number of plants in an area.Also, area covered by vegetation is a good predictor of species numbers for birds (Goldstein et al.1986);mammals,am-phibians,and reptiles (Dickman 1987);and incts (McIntyre 2000).
As over 80% of most central urban areas is covered by pave-ment and buildings (Sukopp and Werner 1982,Blair and Launer 1997),less than 20%,therefore,remains as vegetated area.Furthermore,the remaining vegetated habitat often contains low plant diversity as a result of ero
朋友英文sion,trampling, pollution,invasion or cultivation of a few nonnative species, and many other human disturbances.Also,mowing,prun-ing,and other common landscaping practices further re-duce the volume of the remaining vegetation (Gilbert 1989, Adams 1994).
Suburban diversity: Peak or plunge?Some studies in-dicate that species richness tends to be higher in areas with low to moderate levels of human development (such as out-lying suburban developments) than in more natural rural ar-eas such as prerves.This suburban peak in species numbers is evident in many taxa,such as mammals (Racey and Euler 1982),birds and butterflies (Blair 2001),bumblebees (Pawli-kowski and Pokorniecka 1990),ants (Nuhn and Wright 1979), lizards (Germaine and Wakeling 2000),and plants (Kowarik 1995).
An explanation often suggested for this suburban peak (e.g.,Blair and Launer 1997,Germaine and Wakeling 2000, Blair 2001) is the intermediate disturbance hypothesis.The initial human impacts of suburban sprawl are sometimes relatively mild,with only a few housing subdivisions in a matrix of largely natural or agricultural habitat.This promotes environmental heterogeneity,becau different habitats oc-cur alongside one another.Such habitat diversity is enhanced by the fact that individual homeowners often make individ-ualistic choices in the plants that they cultivate (Henderson et al.1998).
In addition to providing spatial heterogeneity,the an-thropogenic habitats are typically very productive (Falk 1976), being highly subsidized in scarce resources,ranging from water to nutrients (e.g.,fertilizers).Cultivated plants include many ornamentals that often bear fruits and eds that are uti-
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Articles
Figure 2.Urban–rural gradient.This is a very generalized and simplified depiction of changes in surface area,species richness,and composition,as compiled from a number of sources dis-cusd in the text.Two basic conrvation strategies with respect to urban sprawl are shown at the top.
lized by animals,especially birds and bats (Munyenyembe et al.1989,Adams 1994).Some animals have adapted to the di-rect consumption of human resources (Adams 1994) that are provided accidentally (garbage) or intentionally (bird food). In contrast to the above,other studies show that suburban areas have reduced species diversity compared to less-altered rural habitats (figure 2).For example,Marzluff’s (2001) com-pilation of51 bird studies found that 31 of the studies (61%) showed lower species richness in suburban and other areas of human ttlement,compared with more natural rural ar-eas.The remaining 20 studies reported either an increa or no change in diversity with increasing human ttlement. The 51 studies covered a wide range of geographic and nat-ural ttings,so it is difficult to identify which variables de-termine whether a ri or fall of species richness occurs with increasing ttlement and suburban development.
T easing apart the variables,such as the role of the natural tting,is clearly a priority for further work on urban–rural gradients.Bell (1986),for example,has suggested that ur-banization in a tropical rain forest may have different effects on local species richness than urbanization in other natural ttings,becau rain forest birds have exceptional difficulty adapting to human ttlements.
Local extinctions during housing development. Areas of active development tend to have low biodiversity be-cau of the devastating impact on native species of most res-idential and commerci
al development methods.Before con-struction of most residential and commercial buildings,it is common for developers to remove most vegetation and even topsoil (Sharpe et al.1986).This reduces construction costs by allowing equipment ready access to the construction site.
A study of the fate of natural vegetation during urban de-velopment in Wisconsin found that only about one-third of the original vegetation was not destroyed (Sharpe et al.1986). The loss of native vegetation (and total vegetated area) has a negative impact on native animal diversity.Bird species rich-ness declined dramatically in the early stages of housing con-struction (compared to preconstruction diversity) in California (Vale and Vale 1976) and Poland (Luniak 1994).
Once construction is finished,some of the area is paved, which removes it as habitat for nearly all species.In Palo Alto,California,for example,25% of the area of residential communities is covered by pavement (Blair and Launer 1997); another 20% of the area is covered with housing.Of the re-maining nonpaved portions,much is replanted with (usually nonnative) grass,shrubs,and trees (Wasowski and Wa-sowski 2000).
Conrvation strategies.Habitat conrvation can uti-lize prervation and restoration (figure 2).The most effec-tive (and cheapest in the long term) strategy is to prerve as much remnant natural habit
at as possible.Many studies de-scribe how native species richness in a remnant habitat in-creas with the area of that habitat.This is true for many taxa,including birds (Tilghman 1987),mammals (Dickman 1987), and plants (Dawe 1995).
One way to prerve remnants in housing developments is to retain predevelopment vegetation.A number of recent books,such as The Landscaping Revolution(W asowski and W a-sowski 2000),have pointed out the benefits of retaining pre-existing vegetation when building new homes.Unfortunately for conrvation goals,this type of construction is rarely un-dertaken by most residential real estate developers.Although ostensibly related to cheaper costs of mass construction,re-taining more predevelopment vegetation is less expensive in the long term (Dorney et al.1986) and is preferred by many homeowners (Wasowski and Wasowski 2000).
A major influence on natural remnants is the matrix,or the type of habitat,that surrounds them.Remnants are often em-bedded in a highly disturbed matrix that also rves as a con-tinuous source of nonnative species.A major challenge is that remnant habitats are open to colonization by nonnative species of invasive plants (Luken 1997) and predatory animals such as houcats and dogs (Marzluff2001).The nonna-tive invaders and predators can greatly reduce the ability of the remnant habitat to support native species,especially birds.In the language of population biology,thes
e remnants become population “sinks”that are unable to support lf-sustaining populations of the native species. Restoration strategies: Succession and cultivation. Conrvation strategy can also focus on restoring native species in managed and ruderal habitats.In natural ecosys-tems,biotic succession increas the number of plant and an-imal species after a disturbance (Gibson et al.2000).This is also true of ruderal and managed habitats that remain undis-turbed long enough for succession to occur.Various studies have documented how succession increas species diversity in ruderal and managed communities,for example,incread plant diversity in urban lots (Crowe 1979),incread arthro-pod diversity in restored communities (Majer 1997),and in-cread bird species richness in residential communities (V ale and Vale 1976,Munyenyembe et al.1989,Luniak 1994).As a conquence,older residential areas (usually nearer the urban core) tend to have higher species richness than younger ones (e.g.,Munyenyembe et al.1989).
The studies cited above show that the accumulation rate of new species during succession is initially very rapid and is sub-stantially slower after the first few years and especially after the first decades.Aside from increasing total diversity,eco-logical succession also often reduces the diversity of non-native species in an area (Gibson et al.2000),many of which rely on disturbance to sustain their populations (Luken 1997). Another restoration strategy to increa native biodiversity in manag
ed habitats is to cultivate a variety of plant species. Cultivation with native plant species may benefit not only na-tive plant populations but also native animal populations.For example,native bird species richness in Australia (Mun-yenyembe et al.1989) and North America (Sears and Anderson 1991) tends to positively correlate with the volume and species
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