Global Change Ecology (BIO347)

All Strangers are not foes

Conservation writer Emma Marris points that many ecologists and conservationists are prejudiced towards non-native species and preoccupied with the ‘native good and non-native bad’ dogma [1]. ‘non-native bad’ notion has much been influenced by philosophical standpoint regarding ‘nature’ and ‘natural’ and also by some overwhelmimg facts associated with some non-native species which have invaded new areas. An anlysis by Davis wilclove shows that Invasive Alien Species (IAS) is the second largest threat to bidiversity in the United states [2]. Much popular ‘IUCN Red List of Threaned species’ also points that IAS is a major cause of species threat and extinctions particularly of birds, fishes and mammals [3]. Many birds and mammals in oceanic islands have already been wiped out by feral species introduced intentionally or accidently. Brown tree snake on Guam-which eradicated 15 native birds, or the Nile Pearch-which caused extinction of 200 fish epitomises non-native species for many. Ecologists are worried that complex and heterogenous ecosystems are turning towards simple and monotonous with increased non-native species.

Of course, introduced species which turned themselves into invasive are real environmental and economic burden and they deserve management intervention, however, considering all non-natives as negetive appers too simple generalization. Management of invasive species is much influenced by native versus non-native dichotomy as pinted by Mark Davis [4].

‘non-native’ species have been vilified for driving beloved ‘native’ species to extinction and generally polluting ‘natural’ environ­ments. Such characteri­zations have helped to create a pervasive bias against alien species that has been embraced by the public, conservationists….….. throughout the world.

It seems that ‘non-native species bad’ has been taken for granted by many policy makers and ecologists which creates bias towards non-natives. Here, I attempt to show that all non-natives are not bad rather they play role in conservation and restoration. And argue native non-native dichotomy largely overlooks social and ecolgical contribution of non-native species.

Ecologists have documented cases where introduced species have played substantial role to enhance biodiversity. Ascension island in the Atlantic-once considered as very poor by Darwin when he visited almsot 200 years ago- now is substantially richer in biodiversity compred to Darwin’s time. Now the area has been forested, species diversiy has manifolded-only one native tree has been accompained by 39 guest tree species [1]. Dov sax published a much counterintuitive result from a mata-anlysis ivolving all the oceanic islands aross the globe[5]. In the islands species brought by human have outnumbered the extinctin and the richness is higher than that would be in absence of introduction by humans. Ariel Lugo in Puerto Rico found that introduced tree plantation performed better in species diversity, biomass accumulaion and nutrient cycling than the native forests [6]. Similarly, a study comparing plant species richness between introduced and native pine forest in islands of western coast of norway reports higher richness in nn-native plantatins [7]. There are several instances where non-native species have supported and conserved native species by providing food and shelter, conserved rare species and substituted extant taxa [8].

But all biologists and ecologists can not enertain the ‘high biodiversity’ and restored ecosystems that contain non-native species. Instead of getting appreciation for their role in conserving other species and maintining diversity those species are getting an axe from environmental managers simply because they were originated somewhere else. Here ‘non-native bad/unnatural’ notion plays to rejection of diversity by nn-natives.

Contrary to ‘non-native bad’ generalization, there are several instances where non native species have played role in restoring the degraded ecosystems. US forest service scientist John Ewel opion that we can consider non-native species in restoration provided they do not pose serious threat to ecosystem health and provide social and ecological services [9]. Ariel Lugo based on his long term research at Puerto Rico concludes [6]:

The invasion of a site and the formation of an alien dominated forest serve important ecological functions, such as repairing soil structure and fertility, and restoring forest cover and biodiversity at degraded sites.

Pinus patula?, a native of mexican highlands brought to Nepal by Australian foresters has been successfully been used to restore degraded forest in hills of Nepal. This species made ground to regenerate native species. Now native broadleaved species are regenerating luxuriantly under the crown of non-native species.

Most of the extinction of native species particularly birds in ocenic islands is resulted from intertrophic interaction- by predation rather than competition. There are very rare instances of extincation in which introduced plant species is attributable culprit. Plant species do not predate but they may pose threat by altering habiat [10]. Therefore, categorically blaming non-native as cause of extincation is also biased.

Movement of species is pervasive and continous, we accept non-natives in fields, avenue plantations and cityscapes. It is likely that more species will move from one parts of world to other to meet aesthetic and economic needs. Eucalypts and mahogany for timber and cherries for urban beauty are accepted away from their origin. During remote past propagules of species might have transported far away from their historic ranges by storm, floods and birds. Species will move towards cooler places to respond global warming. Currently there are translocations of wildlife to save small population crashing. There are attempt even to introduce wildlife as proxy of extant species [1]. These continous flux of species questions the way non-natives are defined. Who knows, species capable of surviving in new environment may best fit in future climate and land use scenarios.

Spread of non-native species has became common phenomenon, definitely not an exception. Public, plicy makers and scientists should admit that environmenal threat has been posed by a small subset of non-native species. Judging species based on ‘what economic and ecological roles they play in new ecosystems’ may be more smart over judgement based on ‘where they originated’ [4, 11]. Native non-native dichotomy should be abandoned and and new classification of species based on their damage to ecosystem health and biodiversity may help manage non-native based on their ecological and economic roles.

References

1. Marris E. 2011. Rambunctious GardenWilcove DS. 1997. Bioscience:
2. Wilcove DS et al 1997. Bioscience 48(8):607-615
3. IUCN 2004 IUCN Red List of Threatened Species.
4. Davis MA et al.2011. Nature 474:153–154
5. Sax DF. 2004. The American Naturalist. 160(6): 766-783
6. Lugo AE 2004. Frnt Ecol Env. 2(5): 265–273
7. Vetaas OR et al 2013. ?:1-13.
8. Schlaepfer MA et al. 2011. Conservation Biology 25(3): 428-437
9. Ewel JJ, Putz FE. 2004. Front Ecol Environ 2(7): 354–360
10. Davis MA 2003. Bioscience 53(5): 481-489
11. Warren CR 2007. Progress in Human Geography 31(4): 427–446

Lila Nath Sharma