Hi colleagues, =20
Please forgive my late entry into this topic of discussion but I did = want to throw out one or two issues concerning non-native species, invasive non-natives, and biodiversity. =20 One issue that has garnered very little discussion in a global context = is what constitutes a native species. Here in the US, with particular = regard to plants, the argument has always been in favor of the =93cutoff date=94 = being sometime prior to 1492 and the sailing of the =93ocean blue=94 however = in Britain, where much of my initial work on preserving native biodiversity = was developed, the consensus of opinion on a similar moment in history is = seen as the formation of the English channel (and hence the disconnection = from mainland Europe), which was about 9,000 years ago, and includes not only plants that were already there but also those that arrived = =93naturally=94 i.e. as a result of the end of the Ice Age and consequent migration of plants north-west as climate changed and ice retreated- oh, wait does any of = this sound familiar? (By the way, a colleague of mine recently told me that = the Inuit people with whom he works are in a real dilemma because they are having to literally invent language for the first time because up until = now they have not needed the words for =93wasp=94, =93barn owl=94, or = =93tuna!=94) Finding the differentiation between human-created climate change as an = instigator and natural shifts and migrations of certain populations due to a = natural regulation mechanism is rather complex and certainly an emotive topic to = try to delve into, nevertheless as the landbridge and other natural = connections from South and Central America (ocean currents, avian seed dispersal) = create passage from South to North (and vice versa), there could be some very specific examples of species that should perhaps be considered native or properly naturalized (and I am not talking about the inane move to re-classify crape myrtles, Lagerstroemia spp., as now native to = California!) =20 Point number two: that which constitutes non-native and invasive alien = may be an entirely differing set of issues dependent upon context and = locality. Some years ago Christopher Dick (Harvard University) published a very interesting article in the Proceedings of the Royal Society where he = showed that in the absence of native pollinators, some native canopy-emergent tropical trees were being genetically rescued precisely because of the ability of alien pollinators to provide relatively long-distance gene = flow- in this situation, the tropical species was isolated in fragmented = Amazonian pastures (i.e. native pollinators were not =93ousted=94 by the aliens = but were victims of the set of proverbial edge effects created by habitat fragmentation, one of which is to dissuade insect pollinators from = migrating from patch to patch and of course the reduction in core areas, the = habitat for forest dwelling pollinators.) Interestingly the savior happens to be Apis mellifera scutellata, the Africanized honeybee. By the way, my own research in tropical habitats and in particular SLOSS theory and habitat fragmentation was to posit the term and the concept of =93biological corridors=94 some 20 years ago. At that time, although many have = developed my ideas much further, some of my arguments centered not just upon the = seasonal and/or daily migrations of larger animals, but also on preserving the opportunity for plants and invertebrates to secure genetic diversity and reduce reproductive isolation. In many situations around the world, the increased fragmentation of critical habitat, especially in irregularly-shaped patches, and the subsequent reduction in core = interior space has allowed the proliferation and invasion of alien species that = would normally have been better controlled had human disturbance not occurred. =20 Another aspect of the native issue is precisely the preservation of = native biodiversity across the multitude of mutualistic trophic levels. Here in = the District of Columbia, I am involved in the construction of greenroofs = and am attempting to connect them to closely adjacent or virtually contiguous habitat strips constructed as integral to various Low Impact Development (LID) elements such as raingardens and bioretention areas. This has = become the framework for developing a model for using the same corridor concept = in ultra-urban scenarios: the creation of core habitat areas (or = remediation of dysfunctional fragments into areas with more integrity) and linkages = that allow for effective support for biodiversity, whether it be routes of = travel to/from refuge to food, =93grazing=94 territories that must take into = account alternative prey measures as well as seasonal fluctuations, or continued genetic migration to maintain species survival. Central to this project = is the use of native plant species that have historically supported native insect species and so on. The usual arguments of their ability to exist = in =93native=94 climactic conditions aside (i.e. no over-dependence on = water or fertilizers), work by Paula Shrewsbury at the University of Maryland has shown that the provision of alternate prey to natural insect predators = by ensuring a certain amount of species richness in native perennial = selections manages to provide a healthier ecosystem because although the numbers of pests may increase, the persistence of native predators similarly = increases and so a balance is achieved. Further research by Doug Tallamy at the University of Delaware shows exactly how important native woody species = are for preserving native biodiversity where he shows that 90% of all = insects that eat plants require native plants to complete their development = because as plants protect their leaves with toxic chemicals only insects with a = long evolutionary history between themselves and their host plants can = survive after eating those chemicals (i.e. after they have evolved physiological mechanisms for detoxifying them.) Native insects only have such = histories with native plants. They have not been exposed to plants that evolved in Europe or Asia long enough to be able to use them as host plants successfully. Why is this important? Studies have shown that areas = overrun with alien plants produce 35 times less caterpillar biomass, the most popular insect food with birds. Alien plants used in the ornamental = trade support 29 times fewer species of caterpillars than native ornamental plants. (In the mid-Atlantic, native species from the genus Quercus = support 534 spp. pf lepidoptera, Prunus supports 456 spp., Salix 455 spp., = Betula 413 spp. etc. amongst herbaceous perennials, Solidago supports 115 spp., asters support 122 spp., Helianthus 73 spp. Eupatorium 42 spp. etc.) =20 Finally (I guess my one or two points became four) my vote for number = one invasive alien would have to be for the amphibian chytrid fungus Batrachochytrium dendrobatidis, introduced through lab specimens of a = South African frog species (where the disease was a stable endemic infection = in for 23 years before any positive specimen was found outside Africa) and = is the cause of amphibian deaths and population declines across at least = three continents (including Panama, Ecuador, Venezuela, New Zealand, = Australia, and Spain.) =20 David Hilmy Director of Conservation KuTunza Environmental Education Program Europe: 27 avenue de l'Op=E9ra, 75001 Paris, France USA: 2804 Shepherd St., Mount Rainier, MD 20712; 202-316-4902 =20
