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The evolutionary impact of Essay on Reflections, invasive species.
Since the Age of Exploration began, there has been a drastic breaching of in Society, biogeographic barriers that previously had isolated the continental biotas for millions of years. We explore the nature of of Education, these recent biotic exchanges and november germany their consequences on on Reflections of Education evolutionary processes. The direct evidence of evolutionary consequences of the biotic rearrangements is of variable quality, but the study, results of Essay on Philosophies, trajectories are becoming clear as the number of studies increases. There are examples of invasive species altering the evolutionary pathway of shining movie, native species by competitive exclusion, niche displacement, hybridization, introgression, predation, and ultimately extinction. Essay On Philosophies? Invaders themselves evolve in response to their interactions with natives, as well as in shining movie, response to the new abiotic environment. Flexibility in on Reflections of Education, behavior, and shining movie mutualistic interactions, can aid in Essay on Reflections on Philosophies of Education, the success of Essay on Legalization of Prostitution, invaders in their new environment.
Those of Essay of Education, us alive today are witness ing the consequences a number of truly grand, but unplanned, biological experiments. They are the strain theory, result of the activities of on Reflections on Philosophies of Education, a massive human population that is still growing and increasing its impact on the Earth. Because there are no controls on these experiments, as such, we must look to biological patterns through time for perspective on robert merton's theory the consequences of the mixing of on Reflections on Philosophies, biotas. This is a challenge because environments of the past also changed, sometimes abruptly.
These historical fluctuations in on Legalization of Prostitution, climate and on Reflections of Education biota of the past have led some to say that nothing new is Reproduction happening that has not already happened before. The response to Essay on Philosophies, this proposition is yes, but the rate of change in the composition of the atmosphere today exceeds anything of the past, as will the tata motors, consequent rate of climate change. This is also true to a large degree in the extent of migration of species among continents. Before the of Education, Age of Exploration, dispersal of organisms across these great biogeographic barriers was a low-probability event; however, today this is meaning routine. Of Education? In this paper we briefly summarize the consequences of the massive movement of tata case study, organisms across these barriers in terms of the course of future evolution.
We start this essay with two quotes providing perspectives on the problem. One is from the pioneering work of Essay on Reflections on Philosophies, Charles Elton (1), who stated, “We must make no mistake: we are seeing one of the shining movie, great historical convulsions in the world's fauna and on Reflections on Philosophies of Education flora.” Elton certainly had no doubts of the magnitude of the invasive species issue. Essay On Legalization Of Prostitution? More recently, Geerat Vermeij (2) remarked specifically about the evolutionary consequences of this convulsion, “… if newcomers arrive from far away as the Essay on Reflections on Philosophies of Education, result of large-scale alterations in in beowulf, geography or climate, the change in Essay on Reflections on Philosophies, selective regime and the evolutionary responses to motifs, this change could be dramatic.” We examine here some of the evidence for this potentially dramatic scenario.
The Changing Evolutionary Landscape.
It is Essay of Education commonly acknowledged that the revolution, abiotic environment is being greatly altered because of massive land-use alteration and on Philosophies emerging climate change (3, 4). Case Study? However, an of Education, equally drastic alteration is occurring in the composition of biotic communities. The kinds of meaning, physical and biotic environments that exist now are quite different from those that have existed in recent geological times.
International commerce has facilitated the Essay of Education, movement of species; this is Reproduction true globally and across taxonomic groups. Ironically, this has increased species richness in Essay on Philosophies, many places where new species are introduced. The actual numbers of individuals and in literature species being transported across biogeographical barriers every day is presumably enormous. However, only Essay on Reflections on Philosophies of Education a small fraction of those transported species become established, and of these generally only about 1% become pests (5). Over time however, these additions have become substantial. There are now as many alien established plant species in logos in literature, New Zealand as there are native species. Many countries have 20% or more alien species in their floras (6). There are few geographic generalities to these trends; the Essay on Philosophies of Education, strongest is on Legalization of Prostitution that islands, in particular, have been the recipients of the Essay on Philosophies, largest proportional numbers of on Legalization, invaders. Essay? Biotic homogenization within continents is equally as striking as mixing among oceans. As one example, Rahel (7) notes that in the United States pairs of states on average now share 15 more species than they did before European settlement. Of Prostitution? The states of Arizona and Montana, which previously had no fish species in common, now share 33 species in on Reflections, their faunas.
Mack (8) estimates that over human research papers, the last 500 years, invasive species have come to Essay on Reflections on Philosophies, dominate 3% of the Earth's ice-free surface. Vast land or waterscapes, in certain regions, are completely dominated by trafficking research papers, alien species, such as the star thistle Centaurea solstitialis in the rangelands of on Reflections, California, cheatgrass ( Bromus tectorum ) in the intermountain regions of the tata motors, western United States, and water hyacinth ( Eichornia crassipes ) in many tropical lakes and Essay on Reflections on Philosophies of Education rivers.
As the volume of global trade increases, one would expect the on Social, rate of Essay, establishment of alien species to increase also; data support this prediction. Cohen and in literature Carlton (9) noted that the on Philosophies, rate of merton's strain theory, invasion into San Francisco Bay has increased from approximately one new invader per year in the period of of Education, 1851–1960, to more than three new invaders per year in the period of human trafficking papers, 1961–1995. In the Essay on Philosophies of Education, United States the numbers of human trafficking papers, fish introductions, either from on Reflections on Philosophies of Education foreign sources or across watershed boundaries, has increased dramatically. In the in Society, period between 1850 and 1900, 67 species were introduced, between 1901 and 1950, 140 species, and on Philosophies of Education between 1951 and 1996, 488 species (ref. 10 and the web site referred to november revolution germany, therein).
In addition to the greater number of species crossing borders there is Essay on Philosophies also a buildup in theory, the invasive potential of Essay on Reflections of Education, those nonnative species already established in a region, as immigration increases their population sizes. Shining Movie? “Introduced species” may stay at on Reflections on Philosophies, a fairly low population size for revolution years and then explode at some later date—the so-called lag effect. This lag effect may simply be the Essay on Philosophies, result of the shining movie, normal increase in size and distribution of a population. Essay On Reflections On Philosophies Of Education? For instance, Bromus tectorum was introduced to intermountain western North America around 1890, and remained in localized populations for tata motors case 20 years. Essay On Reflections? This lag phase was followed by Essay on Legalization of Prostitution, 20 years of Essay of Education, logistic range expansion; by 1930 B. Essay Of Prostitution? tectorum was dominant over 200,000 km 2 (11).
Crooks and Soule (12) note that in on Reflections, addition to the normal population growth lag phase there are other mechanisms that can keep newly introduced species at on Social in Society, low levels for on Reflections decades before they become invasive. Tata Case? These include environmental change, both biotic and abiotic, after establishment and genetic changes to Essay of Education, the founder populations that enable subsequent spread. Evidence for robert strain theory the former cases is abundant but scarce for the latter.
In summary, the Essay on Philosophies of Education, biotic background for evolution has been changing since the robert, Age of Exploration, and at an ever-accelerating pace because of accumulative effects of the numbers of species involved, the on Philosophies, increased rate of exchange, and shining movie the lag debts that communities have amassed.
There are examples from the past of sudden mixing of Essay on Reflections, biotas that were formerly isolated; one of motifs, these is of Education fairly recent and instructive. In Beowulf? The biota from the of Education, Red Sea and the Mediterranean Sea were reconnected, after a separation of millions of germany, years, by on Philosophies of Education, the construction of the Suez Canal in 1869. The pathway for movement between these water bodies has changed since 1869 because of the varying salinity of a lake in motifs in beowulf, the canal system; that is, there has not been totally free exchange without barriers. On Reflections On Philosophies? Nonetheless, over shining movie, 250 species, 34 new genera, and 13 new families have moved into the Mediterranean Sea from the Red Sea, yet there has only been one documented extinction (13). Essay? These invasions have primarily been accommodated by niche displacements through competitive interactions among the congeners (14). Revolution? Many of the native fish in the Mediterranean have maintained their preinvasion feeding habits but have been displaced in on Philosophies of Education, depth by the Red Sea invaders, which prefer the shallower, warmer, waters at the surface (15). Essay In Society? Two nocturnally foraging fish ( Sargocentron rubrum and on Reflections on Philosophies of Education Pmpheris vanicolensis ) have shown large population increases after invading the Mediterranean from the Red Sea. Night foraging is an logos, uncommon strategy among native Mediterranean fish (only one feeds at Essay on Reflections, night), hence these migrants were probably successful because this novel behavior allowed them to exploit resources that the native fauna had not yet used.
There have been a number of logos, spectacular population explosions of the Red Sea immigrants through time, most of which have eventually become reduced in size (14). An exception is Rhopilema nomadica , a large Red Sea jellyfish that experiences population explosions and Essay on Philosophies crashes each summer off the coast of Israel.
The Great American Interchange of biota, the result of the merton's strain, isthmian land bridge that formed during the Late Pliocene, provides further information on the consequences of the Essay on Reflections on Philosophies, mixing of previously isolated biota. However, the course of temporal resolution of the information available does not make it possible to motifs in beowulf, say with certainty whether the on Philosophies of Education, losses of biota that occurred subsequent to the bridge were due to robert theory, competition with new arrivals, although it appears likely (16). On Reflections On Philosophies Of Education? The effects of the interchange apparently were asymmetrical, with the immigrants from the november germany, south “insinuating” into Essay on Reflections of Education the northern biota, whereas the northern immigrants to the south may have caused extinctions and undergone subsequent evolutionary radiation (17).
What we lack is detailed information on shining movie the impacts of the exchanges of Essay, biota on november revolution time frames greater than centuries but less than millions of Essay on Philosophies, years. Logos In Literature? In the century time frames we have processes that are still in Essay, a state of shining movie, flux at the community level and ones that have been that have not been studied in detail. In the Essay on Reflections of Education, geological time frame, the poor temporal resolution does not permit us to clearly understand the mechanisms that have led to in Society, what we see in on Philosophies of Education, the fossil record.
The Direct Evolutionary Consequences of shining movie, Mixing.
Evolutionary Adjustments of Invaders and on Reflections of the Invaded.
We turn to november revolution, contemporary studies to Essay on Reflections on Philosophies, give us some indication of the germany, evolutionary impact of invasive species. Essay On Reflections Of Education? Recent studies have shown that invaders can rapidly adapt to Essay on Legalization of Prostitution, the new environments in which they find themselves. Huey et al. (18) demonstrated how an introduction of on Reflections of Education, a new fruit fly into the west coast of North America resulted in Essay on Social in Society, the evolution, in on Reflections of Education, only 20 years, of an motors, apparently adaptive cline related to wing size, throughout the vast new latitudinal range extending from southern California to on Reflections on Philosophies of Education, British Columbia. The cline that developed in human research, North American female flies was similar to that found in the European native populations. On Philosophies Of Education? Interestingly, the in beowulf, developmental basis for the cline of Essay on Reflections of Education, wing size was different in Europe than for the invader in motifs, North America, although the functional result was the Essay on Philosophies, same, providing additional evidence for the adaptive advantage of merton's strain, this set of traits.
Drosphilia subobscura were introduced into North America in on Reflections of Education, 1982; shortly thereafter Ayala et al. (19) described the invasion as “a grand experiment in evolution.” This was certainly an november germany, accurate prediction, given the of Education, results of Huey et al. 10 years later, and logos meaning in literature only 20 years after the beginning of the invasion event.
There are other documented instances of an invading species adapting to Essay on Philosophies of Education, its new environment. Essay On Social Reproduction In Society? For example, Johnston and Selander (20) described the evolution of apparently adaptive clines in body size and feather color in English sparrows that were introduced into Essay on Philosophies North America in 1852 and that subsequently established a large geographical range. Robert Merton's? Further, Cody and Overton (21) described the Essay, reduction in revolution germany, distance of dispersability for wind-dispersed seeds of invasive species onto Essay on Reflections on Philosophies of Education, islands in research papers, just a few generations in small isolated populations. Similarly, Losos et al. (22) demonstrated that within 10–14 years species of lizards introduced onto Essay on Philosophies, a series of logos meaning in literature, island in Essay on Reflections of Education, the Caribbean showed adaptive morphological adjustments.
There are also examples of relatively rapid, nonadaptive, genetic change of invaders as seen in house mice introduced into Madeira; localized differentiation of chromosomal races is the result of robert merton's, genetic drift in isolated valleys (23). Essay On Philosophies Of Education? Similarly, genetic drift has been responsible for geographic genetic patterns found in meaning in literature, the introduced Bufo marinus in Essay on Reflections on Philosophies of Education, Australia (24).
Evolution in Response to an Invader.
There are also examples of in beowulf, rapid evolution in on Reflections, native species in Essay on Social Reproduction in Society, response to on Reflections on Philosophies of Education, an introduced species. Trafficking? Carrol and Essay on Reflections Dingle (25) indicate that populations of the soapberry bug ( Jadera hematoloma ) have evolved differing beak lengths in response to the introduction of Reproduction in Society, new invasive hosts, within only 50 years time. Singer et al. (26) have shown rapid evolution in on Philosophies, the feeding preferences of the tata study, Euphydras butterfly for on Philosophies of Education the invading herb, Plantago lanceolata.
Zimmerman (27) documents an motifs in beowulf, interesting case of evolution in response to an introduced crop species. Of Education? At least five species of host-specific moths ( Hedylepta ) have evolved since the introduction of motifs, banana into Hawaii ≈1,000 years ago. Essay Of Education? These species were threatened at motifs in beowulf, the time of on Reflections of Education, Zimmerman's study by parasitic wasps and flies introduced for agricultural pest control.
There is a large literature on the evolution of of Prostitution, weeds in Essay, response to human activities, including agricultural practices. Shining Movie? Harlan (28) noted that some weeds have evolved to be crop mimics. Essay On Philosophies Of Education? Not only are they are similar in their phenological development and morphological appearance to the crops with which they have co-evolved, but also their seeds have evolved a similar appearance so they are not sorted and discarded during harvesting. On Social Reproduction? For example, the lentil mimic ( Vicia sativa ) has evolved a seed shape and Essay on Reflections on Philosophies of Education color comparable to Essay on Legalization of Prostitution, the lentil ( Lens culinaris ). Essay On Reflections? This trait is under control of a single gene. Similarly, Echinochloa crus-galli has evolved mimics to rice, Oryza sativa , which are very difficult to tata motors study, distinguish from the crop.
De Wet and on Reflections of Education Harlan (29) surmised that many plant weeds might have evolved from Essay natural pioneer species associated with continuous disturbance by humans. Essay On Reflections On Philosophies Of Education? Some weeds that have developed in in literature, association with agriculture have become crop mimics as described above. On Reflections? Weeds are also derived from in beowulf hybridization and introgression with crops as happened with Johnson grass ( Sorghum halepense ) and the cultivated Sorghum bicolor . Essay Of Education? Weeds have also evolved from abandoned domesticated plants.
Thus there are many cases that have been documented of the evolutionary response to the new environment that an on Social Reproduction in Society, invasive species may encounter as well as cases of the adaptive response of organisms to a new invader.
In addition to direct evolutionary responses of Essay on Philosophies of Education, organisms involved in invasions there are also very important indirect effects through changes in motors study, the genetic structure of invasive species in relation to Essay, the new organisms that they encounter. Motifs In Beowulf? These major effects are related to hybridization and introgression. Rhymer and on Philosophies of Education Simberloff (30) have recently summarized our knowledge in shining movie, this area. There are many examples extending over many different taxonomic groups, a few of which are noted below. These authors conclude that in on Reflections of Education, the case of invasive species hybridization with native species can cause a loss in fitness in the latter and robert merton's theory even a threat of extinction. McMillan and Wilcove (31) have documented that of 3 of Essay, 24 species listed as Endangered in the United States and tata case that subsequently went extinct, 3 were the result of hybridization with alien species.
Birds—Mallard ducks ( Anas platyrhynchos ) that have been introduced into various regions of the world have had large genetic effects. They have hybridized and reduced populations of the New Zealand gray duck ( Anas superciliosa superciliosa ), the Hawaiian duck ( Anas wyvilliana ), and the Florida mottled duck ( Anas fulvigula fulvigula ) (30).
Mammals—Sitka deer ( Cervus nippon ) were introduced into Great Britain from Japan over a hundred years ago. They have hybridized with the Essay on Philosophies, native reed deer ( Cervus elephaus ) although they are different in body size. Motifs? It appears that the Essay, genetic integrity of the in beowulf, native red deer is threatened in on Reflections on Philosophies, some regions (32).
Fish—There are a number of cases of human research papers, hybridization and Essay on Philosophies subsequent introgression in fish, primarily game fish where there are massive introductions of foreign stock. These include trout in western and eastern United States as well as in Essay, Europe (33, 34). On Reflections On Philosophies Of Education? It has been shown, however, that even small introductions of nonnative species can have large impacts on shining movie the genetics of on Reflections on Philosophies, native species through hybridization and introgression, as was found for native pupfish in Texas (33).
Plants—Abbott (35) notes that of 2,834 species listed in the New Flora of the British Isles 1,264 are aliens. Human? There are 70 recognized hybrids between native and alien species and 21 between aliens. About half of Essay on Reflections of Education, these hybrids show some degree of merton's theory, fertility.
There are many examples of the on Philosophies, large populations of invading species swamping small populations of native species by theory, hybridization, but in Essay on Reflections, certain cases small populations of an invader can threaten native species that have much larger populations. Shining Movie? This is the Essay on Reflections on Philosophies, case with the invading Spartina alterniflora into the San Francisco Bay. It hybridizes with the native Spartina foliosa. In Beowulf? The invader has a higher pollen output, and Essay on Reflections greater male fitness, than the human trafficking research papers, native species and the hybrids and it occupy lower intertidal habitats. In time introgression will threaten the native species (36). Conversely, small populations of rare species can be threatened by of Education, hybridization in logos, a number of on Reflections of Education, ways (37), including infertility of the Essay on Social Reproduction, hybrids.
Small populations on on Reflections of Education islands are particularly vulnerable to tata, extinction by hybridization because they are often less genetically divergent than mainland species and have weak crossing barriers as well as unspecialized pollinators. On Reflections Of Education? Levin et al. (37) describe a number of study, cases of extinction by hybridization on on Philosophies of Education islands, including the endemic shrub Cercocarpus traskaei with the widespread Cercocarpus betuloides and Essay the endangered Lotus scoparius traskiae with the on Philosophies of Education, Lotus argophyllus o rnithopus . They specifically note that introductions may threaten rare species on logos in literature islands and of Education give a number of examples from around the in Society, world, including threats to the rare Arbutus canariensis and on Philosophies Senecio teneriffae on the Canary Islands, Gossypium tomentosum on the Hawaiian Islands, and Pinguicula vulgaris and Linaria vulgaris in the British Islands. Tata Motors Case Study? They posit that the threat of of Education, extinction of rare species by on Legalization, hybridization is Essay of Education very high and that habitat disruption and shining movie invasive species are increasing this threat to the degree that conservation programs should strive to isolate rare species from on Reflections on Philosophies cross-compatible congeners.
The Origin of New Taxa Through Hybridization and Introgression.
While hybridization with invaders can be a threat to species integrity, it can also be a source of new variation and the origin of human research, new species. On Reflections Of Education? Spartina alterniflora from the east coast of North America was introduced into Southampton in on Social Reproduction in Society, shipping ballast in the early 19th Century. It subsequently hybridized with the Essay on Reflections on Philosophies of Education, local Spartina maritima, producing a sterile hybrid. The hybrid in trafficking research, turn underwent chromosome doubling to produce the new fertile species, Spartina anglica. Spartina anglica has become very aggressive and Essay on Reflections occupies large areas of the coastline of the British Isles while at tata motors study, the same time the on Philosophies of Education, original invader, Spartina alterniflora , and the native Spartina maritima have maintained limited distributions. The new polyploid evidently has characteristics that enable it to occupy bare tidal flats that were not available to the parents (38). This event was apparently serendipitous and human research papers has not been replicated artificially (39).
In addition to the Spartina anglica there are other cases of alloploids that have originated from hybridization of native and on Reflections of Education invasive species. These include species of meaning in literature, Tragopogon in North America and Senecio in Essay on Reflections on Philosophies of Education, Great Britain (35).
There are also examples of logos in literature, introgressive hybrids between native and weedy species becoming stabilized to of Education, form new taxa. The introduced Helianthus annuus hybridized with native Helianthus debilia . The hybrids adapted to the new conditions it encountered to form the subspecies Helianthus annuus texanus . Merton's? Abbott (35) cites six such cases of origins of new taxa.
The Indirect Evolutionary Consequences of Mixing.
In addition to the evolution of on Reflections on Philosophies of Education, traits to adapt to shining movie, new environments and to new invaders there are cases of on Philosophies of Education, behavioral shifts in Essay on Social Reproduction in Society, the invaders themselves or in response to invaders. Essay On Reflections? Holway and Suarez (40) give examples of shifts in behavior of populations of merton's strain theory, invading species from that found in their native ranges. Two ant species originating from Argentina (the fire ant Solenopsis invicta and Essay on Reflections on Philosophies of Education the Argentine ant Linepirtma humile ) both exhibit these shifts. It is robert theory not known whether these shifts are founder effects or adaptive. These authors make the case that behavior should be more fully incorporated into Essay on Reflections of Education research as we build an understanding of the invasion process.
The introduction of brown trout into the streams of New Zealand started in the mid-1800s. They have driven to extinction some local populations of native fish and, in addition, they have evidently resulted in changed behavior of motifs in beowulf, native mayfly nymphs and, to a certain extent, crayfish (41).
In addition to Essay, behavioral shifts, either in trafficking research papers, response to an invader or in response to on Reflections of Education, the new biotic community that an invader encounters, shifts in traits have been observed in an invader in a new environment. Essay On Social In Society? Blossey and Notzold (42) note that in of Education, populations of theory, invasive species, the of Education, individuals are often larger in their new territory than in their native land. They compared plants from populations from the logos in literature, United States and as well as those from Europe where they are subject to natural predation in on Philosophies of Education, their native habitat. They attributed the november, size differences to Essay on Philosophies of Education, the consequences of natural selection for greater competitive capacity after release from herbivore attack and november revolution germany the need to produce defensive compounds. Although this particular explanation has been challenged (43), others have noted similar cases of this phenomenon in Essay on Reflections on Philosophies, comparing invading plants from Australia into California (44) and motifs comparing invasions from on Reflections on Philosophies of Education South Africa into Australia and of Prostitution vice versa (45).
Invasive ants may also benefit from release from native pathogen populations, leading to on Reflections on Philosophies, larger colony size that confers greater exploitative competitive capacity, as discussed in Holway (46) and Human and case Gordon (47) (see below). Colonies of invasive Argentine ants are larger in areas where they invade than they are in Essay, their native habitat.
Gray squirrels ( Sciurus carolinensis ) from North America have displaced the native red squirrel ( Sciurus vulgaris ) throughout most of the deciduous and shining movie mixed woodlands of Britain. Essay Of Education? This displacement apparently has resulted from food competition between these species, with gray squirrels favored by high quantities of oaks in the canopy. Tata Case Study? Recent decline of hazelnuts over oaks has evidently contributed to the demise of the red squirrel (48).
There has been a detailed study of the Essay on Reflections, interaction between a California native mudsnail, Cerithidea californica, and an invasive mudsnail, Ilyanassa obsoleta , from the American Atlantic. Populations of Ilyanassa have locally displaced Cerithidea from the open tidal flats, restricting its distribution to Essay on Legalization, the upper intertidal area. Essay On Philosophies? Cerithidea 's former functional role has been taken over by Ilyanassa (49).
Douglas et al. Shining Movie? (50) have described the apparent niche shift in the native fish Meda fulgida when they co-occur with the Essay on Reflections on Philosophies of Education, introduced red shiner ( Cyprinella lutrensis ).
Some invasive species completely eliminate native species through competitive exclusion. The invasive fire ant ( Solenopsis invicta ), for revolution example, has had a devastating effect on the arthropod biota that it encounters. In a detailed study in of Education, Texas, it was found that this fire ant reduced native ant diversity by robert merton's, 70% and the total number of native ant individuals by 90%, apparently by competitive exclusion. Similarly, overall non-ant arthropod diversity was reduced by Essay on Reflections, 30% and the numbers of motors study, individuals by 70% (51). It should be noted, however, that while the Essay of Education, fire ants excluded some native species from the invaded areas, the november, natives persisted in nearby uninvaded areas, such that no extinctions were observed.
The Argentine ant ( Linepithema humile ) is on Reflections on Philosophies of Education a widely distributed invasive species that displaces native ants throughout its introduced range. Shining Movie? It does so by being a better competitor for food resources than the native species (46, 47).
There are accumulating studies examining the on Reflections of Education, mechanisms of shining movie, competitive displacement of Essay on Reflections on Philosophies, native species by research papers, invaders. As examples, superior competition for food resources has resulted in on Reflections on Philosophies of Education, the replacement of the native gecko, Lepidodactylus lugubris , by motifs in beowulf, the invading Hemidactylus frenatus , throughout the Essay on Reflections on Philosophies of Education, Pacific (52). A higher resource-use efficiency of the Essay, available food resources has been implicated in the competitive superiority of the Essay on Reflections on Philosophies of Education, introduced snail Batillaria attramentaria over the native mud snail Cerithidea californica in the salt marshes and mud flats of northern California (53). Tata Motors Case? Studies have also shown that behavioral differences in Essay on Reflections on Philosophies of Education, aggression and predation between a native and revolution germany an invading amphipod explain competitive displacement (54). Essay On Philosophies? Competition for space by the invading mussel Mytilus galloprovincialis from southern Europe has displaced native mussels in California and South Africa (55).
Studies of such new interactions, brought about by invaders, are particularly revealing on the nature of competition because in “stable” ecosystems, with a long history of competition among its members, the resulting evolution of niche displacement makes it more difficult to observe the direct competitive process.
In any ecosystem there is human trafficking research a web of interaction among the on Philosophies, biotic components of differing specificities. Mutualisms, the november, tightest of Essay on Reflections on Philosophies of Education, such interactions, would seem to be a barrier to the success of a single player of a partnership becoming an invasive species. There is some evidence for this in meaning in literature, the fact that nonmycorrhizal (i.e., do not depend on mutualistic root fungi) plant taxa, such as the Brassicaceae and the Chenopodiaceae, are particularly successful weeds. However, quite often the Essay on Philosophies of Education, tightness of tata case, mutualisms is not as great as supposed and Essay on Philosophies of Education other species in the new habitat can play the required role for the invader (e.g., pollination). Tata Case Study? There are also examples of the Essay on Philosophies, arrival of one nonnative species, and the subsequent arrival of a co-evolved facilitator, thereby increasing the success of Essay on Legalization, each in its new environment. This has happened with Pinus spp. and their mutualistic mycorrhizal fungi in the Southern Hemisphere; Richardson et al. (56) describe these as well as other examples.
With the on Reflections on Philosophies of Education, mixing of biota and thus new interaction potentials there is the great possibility of new kinds of mutualistic relationships evolving. Human Trafficking Papers? Richardson et al. (56) note several such cases, including the Essay, dispersal of of Prostitution, North American and European pine seeds, which are normally wind-dispersed, being dispersed into new areas by cockatoos and European pines being dispersed in South Africa by alien American squirrels. Simberloff and Von Holle (57) also note cases of one invading species facilitating the success of another, including a bird of Asian origin being the Essay on Philosophies of Education, prime disperser of a shrub from the Essay on Legalization, Canary Islands, all in their new Hawaiian home.
There are also instances of an invasive species disrupting mutualistic relationships (58). Native seed-harvesting ants disperse the seeds of certain proteas in South Africa. Essay? These native ants have been displaced by Reproduction in Society, Argentine ants that are not successful in dispersing the Essay on Reflections, Protea seeds to meaning, suitable germination microsites, thus potentially leading to the extinction of rare and of Education endemic Protea species.
Finally, there are striking examples of host shifts as species are mixed through invasions and a parasite of one infects the other which is less able to in beowulf, cope with the parasite, as is happening with the parasitic mite Varroa jacobsoni, which evolved as a brood parasite of the Asian hive bee, Apis cerana , but which has now also switched host to the western honeybee, Apis mellifera , with disastrous results (59).
Invasive species not only Essay on Philosophies of Education alter competitive interactions and reduce native populations within a community but they can also lead to extinctions. Overall they are considered the second greatest threat to on Legalization, imperiled species in the United States (60). Carlton et al. Essay On Reflections? (55) make the useful distinction among extinction events as local, regional, or global extinctions. On Legalization? They also recognize functional extinctions where individuals of a species are so reduced in numbers that they no longer play a major role in ecosystem processes. Essay On Philosophies Of Education? Thus there is a large continuum of impacts, with the main concern and logos statistical information available on on Reflections of Education the total global extinction of a species whereas, of course, local extinctions and population reductions are important in Essay on Social, ecosystem functional considerations as noted by Carlton et al.
The literature abounds with examples of Essay on Philosophies, invasive species driving local native species to Reproduction in Society, extinction, primarily on Essay on Reflections islands, and especially involving predators. Merton's Theory? Rodda et al. (61) detail the Essay on Reflections on Philosophies of Education, particularly dramatic case of the impact of the revolution, invasive brown tree snake ( Boiga irregularis ) on Essay on Philosophies of Education the biota of Guam, which has caused a major conservation crisis through negative effects on birds, reptiles, and mammals. In a review of the Essay of Prostitution, impacts of Essay on Reflections, introduced species on reptiles on human islands Case and on Reflections Bolger (62) note that, “Although competition has led to robert merton's strain theory, changes in abundance and Essay has caused habitat displacement and reduced colonization success, extinctions of established reptile populations usually occur only shining movie as a result of predation.” They do note the on Reflections on Philosophies of Education, large number of examples of the research papers, latter that have occurred as a result of predation by rats, feral cats, and Essay on Philosophies of Education mongooses.
It has been well documented that of human research, all ecosystems lakes and on Reflections streams have been most modified by invasive species, mainly because of the persistent efforts of humans to stock with game fish. Many of the meaning in literature, introductions into these bodies result in species enrichment rather than extirpation (63). Essay On Reflections Of Education? However, one of the most spectacular example of meaning, species extinctions in lakes comes from the introduction of the Nile perch into Lake Victoria, resulting in of Education, the loss of hundreds of human trafficking, species of Essay, cichlid fish (64). Shining Movie? Ricciardi and Rasmussen (65) call attention to Essay on Reflections of Education, the fact that the freshwater fauna of shining movie, temperate North America has extinction rates matching that of tropical forests, in part because of invasive species. Ricciardi et al. On Reflections? (66), for example, note a global pattern, that within 4–8 years after invasion by in beowulf, zebra mussel ( Dreissena polymorpha ) local native mussel populations are extirpated. On Reflections On Philosophies? Over 60 endemic mussel species of the robert merton's strain theory, Mississippi River Basin are threatened with global extinction by the effects of zebra mussel and environmental degradation.
Although the introduction of an organism into Essay on Philosophies a new environment always provides risks and motors surprises as to on Reflections on Philosophies, the impact it will have on other organisms, it is research particularly disconcerting when organisms that are introduced to on Reflections on Philosophies of Education, control the shining movie, activities of an unwanted invader instead do collateral damage to Essay on Reflections on Philosophies, other species, even driving them to extinction. This is apparently the on Social Reproduction in Society, case with the introduction of the rosy wolf snail, Euglandina rosea , which was imported into on Reflections on Philosophies Hawaii in 1958 to motors, control the Essay, giant African snail, Achatina fulica . Unfortunately, Euglandina did not restrict its predatory activity to shining movie, the African snail but also attacked rare native Hawaiian snails (67), apparently driving some to Essay on Reflections on Philosophies, extinction. Between 1977 and tata motors study 1987 E. rosea pushed the endemic tree snails of the island of on Philosophies of Education, Moorea to extinction (68). There is november revolution another extinction crisis in the making with the movement of Cactoblastis cactorum from its point of introduction for the control of Opuntia in on Reflections on Philosophies, the Caribbean, to a trajectory that will bring it to a center of diversity of Opuntia in Mexico (H. G. Zimmermann, personal communication).
There have been attempts to give us some sense of the ultimate result of the study, mixing of the biota of world. Essay On Philosophies? Brown (69) has calculated, based on species–area relationships, the revolution germany, worst-case scenario for the impact of free exchange of biotic material across former biogeographic barriers. This was done assuming the Earth's land surface was contained into one supercontinent but that the current climates and geological features were maintained. With these assumptions there would be massive decrease in species, amounting to 65.7% for land mammals, 47.6% for land birds, 35% for butterflies, and 70.5% for Essay on Reflections on Philosophies angiosperms. Logos In Literature? McKinney (70) has made similar calculations for on Philosophies the ocean and Essay concludes that there would be a reduction of Essay on Reflections on Philosophies of Education, about 58% in november germany, the current diversity. McKinney points out, however, that for the theory to be fulfilled there would have to be unfiltered faunal exchange around the on Reflections on Philosophies, world and Essay in Society the lack of physical variability. McKinney notes that it is because these conditions are not fulfilled that we have not seen extinctions in relation to on Reflections, the Suez Canal exchanges.
In the course of this review we have discussed the trafficking research papers, mechanisms by Essay on Reflections, which invasive species evolve in meaning in literature, response to on Reflections on Philosophies of Education, their new biotic and abiotic environments, and on Social in Society how invasive species have altered the evolutionary trajectory of native species with which they interact. Essay On Reflections On Philosophies? While it is Essay on Legalization not surprising that an invasive species would evolve in of Education, their new habitat in response to merton's strain, a new set of selective pressures, it is surprising that there are a number of clear examples of evolutionary shifts in on Reflections, native species in response to the presence of human, invaders, given the small number of generations involved in Essay on Reflections, interactions, and the short period for which such interactions have been studied by ecologists and evolutionary biologists. Much of the evidence we have reviewed has been observed in human, islands, reinforcing what we know of on Reflections, islands as evolutionary hotspots. While few generalizations can be made across taxa and across environments, we can venture a few tentative conclusions. First, invasive predators may have the most dramatic effects, as the shining movie, extinctions they cause represent an on Reflections on Philosophies of Education, irreversible removal of evolutionary potential. Second, few examples of extinction have been associated with competitive interactions. Motifs? This indicates either that extinction by competition is on Reflections a slower process than extinction by predation, such that the Essay, end product of the process is not likely to Essay on Philosophies, be observed on the time scale of most scientific studies, or that communities are not as “full” as most ecological theories presume. Third, interactions between invasive and native biota demonstrate how global changes that alter community structure can have persistent and unexpected consequences.
The biota of the Earth is undergoing a dramatic transformation. Essay On Legalization? The spatial patterning, structure, and functioning of most of the ecosystems of the world have been altered by Essay on Philosophies of Education, the activities of humankind. Merton's? There is Essay on Reflections on Philosophies every indication that these trends will intensify as the size of the human population continues to grow, even in systems that have been set aside for tata motors case protection, because of the Essay on Reflections of Education, global changes that have been set in motifs, motion that are affecting the atmosphere and Essay on Reflections on Philosophies of Education the climate. Essay Of Prostitution? Although some aspects of global change, such as climate change, may be reversed by societal actions, this will not be possible for biotic exchange. The mixing of formerly separated biota, and the extinctions these introductions may cause, are essentially irreversible. Essay On Reflections? Since the shining movie, beginnings of the Age of Exploration, humans have purposefully and inadvertently moved biological material across barriers that, for recent evolutionary time, have separated the unique biotic realms of the continental land masses. We are now developing a whole new cosmopolitan assemblage of organisms across the surface of the Essay on Reflections on Philosophies of Education, Earth with large consequences not only for the functioning of ecosystems but also for the future evolutionary trajectory of tata motors case, life.
This paper was presented at on Philosophies, the National Academy of Sciences colloquium, “The Future of Evolution,” held March 16–20, 2000, at the Arnold and Mabel Beckman Center in Irvine, CA.<
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