The Impact of Alien Species on South African Diversity - Essay Example

The Positive and Negative Impact of Alien Species on South African Diversity Introduction The biodiversity of Southern Africa is one of the richest in the world. It has been totalled that the area maintains 10,000 known marine fauna and flora species (Branch, 2005). Many of these species are endemic to the region, and therefore are particularly susceptible to extinction, as there will be no other place to find them, if it happens that they're overtaken by invasive alien species. Thorough research has been done on both indigenous land and indigenous ocean life in these areas. Likewise, investigations have been designed around further evaluation of the endemic species' alien competitors. In the oceans, the indigenous mussel Perna perna has lost much of its habitat to the alien mussel Scutellastra argenvillei on the western coastline of South Africa. However, on the southern coastlines, loss of mussel Perna perna's habitat has not been as extensive to the competing Mediterranean native mussel Mytilis galloprovincialis. On land, acacia species have been most detrimental to the bioregion, as their land usage expands rapidly. Mature acacias proliferate their seeds and access huge expanses of land. The acacia species Acacia dealbata, Acacia mearnsii, Acacia longifolia, Acacia baileyana, Acacia decurrens, and Acacia Cyclops have overtaken more indigenous species, by changing soil nutrition and taking habitat. The difficulty in controlling acacias is problematic due to the community's use of many acacia species as kindling. Likewise, acacia species stabilise the soil; indeed they were introduced by agriculturalists for the very reason. While having stabilized the soil, they've encroached on the South African fynbos vegetation. At the same time, the increased agricultural usage of the land has hindered the nesting habits of the bird species Black Harriet Circus maurus. In order to counter the multiple problems associated with the acacia encroachment, researchers searched for natural enemy wasps of the Bruchophagus line, specifically Bruchophagus acaciae, Bruchophagus orarius, and Bruchophagus interior, with the purpose of hindering acacia seed proliferation. The acacia has not been the only species introduced for the purpose of stabilizing the soil. Marram grasses were introduced in order to stabilise shifting sand dunes that flooded the South African plains and made agriculture difficult. The Marram grass Amophilia arenaria has been praised for its ability to provide an amiable habitat for the native species of the area. Due to the complexity of alien species and their influences to the diversity of native flora and fauna, investigations and attempts have been made to counteract the process, or at very least, record it. South African Biodiversity Biodiversity along the Southern African shorelines is unique in that its species have evolved and thrived due to the confluence of two distinct water masses. The Agulhas current flows alongside the eastern shores of South Africa, while the west coast is characterised by colder deeper waters (Peschack, 2005). The flora and fauna that immigrant settlers found here is one of the most specific in the world. In southern Africa, 12% of plant species are endemic (Willis et al. 1996, in Mehta 2000).Moreover, the floristic region of the Cape is one of only six on Earth (Branch, 2005). The importance of maintaining the integrity of South African Cape ecosystem cannot be understated. However, many invasive species have invaded the bioregion and caused concern, beginning in the 1700s. At this time, immigrant settlements that came to South Africa began practises of irrigation and livestock raising that negatively affected soil nutrition and made the soil thinner. Consequently, native vegetation species diminished due to poor soil quality (Mehta, 2000). That trend has continued and become multifaceted, affecting both land and ocean species. Negative Impacts of Alien Species on Land Indeed, the most widely studied intruders on the South African Cape region's fynbos vegetation is acacia family. In 2001, Henderson compiled an overview of the most concerning species, citing six for control: Acacia dealbata, Acacia mearnsii, Acacia longifolia, Acacia baileyana, Acacia decurrens, and Acacia Cyclops (from Neser & Prinsloo, 2004). The family of Acacias invading southern Africa is diverse. HERE One of the first introduced land species was the Australian acacia saligna, which "not only invades quickly but also transforms the quality of the soil structure, soil chemistry, and hydrology to better suit its own needs" (Richardson, 1997, in Mehta, 2000). The saligna species was that introduced in the 1700s. Since then, other Australian acacia populations have similarly encroached upon South African soil. Acacia mearnsii and Acacia dealbata, two wattle species, were studied for their spread upon the Drakensberg region (De Neergaard, Saarnak, Hill, Khanyile, Martinez Berzosa, & Birch-Thomsen, 2005). Interestingly, these two wattle species have been partially welcomed by the rural communities, as they are used for kindling and may be utilized as fodder for agriculture (De Neergaard et al). However, the duality of this encroachment is that although Acacia dealbata and Acacia mearnsii may be utilized, their use as fodder changes the Nitrogen content in the soil to an unacceptable level. Whilst the community desire the continuation of the invasive wattle species, the goal of containing it is unrealistic and not likely to succeed. In the process of hoping to contain invasive Australian and New Zealand acacia species in South Africa, many methods have been attempted. An interesting method investigated by Neser and Prinsloo (2004) was the introduction of natural-enemy wasp species. Researchers searched for suitable enemies to counter the explosion of acacias in South Africa and found three Bruchophagus wasps: Bruchophagus acaciae, Bruchophagus orarius, and Bruchophagus interior. This was a pragmatic approach, as all three wasps are seed-feeding species, and the acacia problem in South Africa is proliferated by its seeding. Although in some cases, invasive species such as Marram grasses have been beneficial to the native fynbos, as well as beneficial to the human settlements of the region. The grasses stabilise sand dunes and provide opportunity for agriculture. However, the existence of that said agriculture has caused problems for other species. A case in point is the Black Harriet Circus maurus. Odette, Simmons and Jenkins (2004) studied the feeding and nesting habits of the bird species. They found that although there was evidence the birds foraged among the cereal crops, that they were averse to nesting in those areas. Instead, their nesting habits were concentrated specifically in the non-cultivated montane environments and wetland environments. The difficulty found was that the Black Harriet Circus maurus nested poorly except in the wetlands. In montane regions, their eggs were susceptible and often consumed by predators. Negative Impacts of Alien Oceanic Species Perhaps the most interesting invasive mussel species to the diversity off the ocean waters of Southern Africa is the mussel Mytilis galloprovincialis, which arrived from its native Mediterranean habitat in the 1970s (Branch, 2005, Steffani & Branch, 2004). Ruis and McQuaid (2006) discuss the competitive interaction in their overlapping habitat regions off the Southern Cape. The native mussel Perna perna habitates the lower region while the superior waters to it are habituated by the mussel Mytilis galloprovincialis. Observing the process of their competitive interaction, Ruis and McQuaid transplanted high density populations of both species. Preliminary results of this study did not assist in any conclusion, as ocean patterns incited higher rates of mortality for the invasive and native species equally. The outcome of a conclusion had been desired and was particularly important for the fact that the invasive Mytilis galloprovincialis species had already overborne the habitat of the native Perna perna species on the western coast (Brownes & McQuaid, 2006). When Brownes and McQuaid further studied the two species on the southern coast, they found, surprisingly, that on the southern coast, the mussel Perna perna did not face the same danger from the invasive species mussel Mytilis galloprovincialis. Not all mussel species are quite so easy for Perna perna to defend itself against, for example, mytilis galloprovincialis. The species Scutellastra argenvillei which has encroached the western coast, is replacing and is likely to wipe-out the indigenous mussel Perna perna (Steffani & Branch, 2005). Positive Invasive Species on Land Mehta states that the introduced Acacia saligna species was introduced with the intention of stabilizing the soil (although we know presently, that the reign of acacias has not been appreciated). In much the same way, Marram grasses have benefited the land for stabilizing the soil. Marram grasses, Amophilia arenaria, were introduced in order to stabilize the sandy soil that typifies the South African coastlines (Lukbe & Hertling, 2001). This particular Marram grass has long been used for dune stabilisation, on the west coast of North America as well as in South Africa (Lubke & Hertling, 2001). Settlers introduced in as early as the 1870s for artificial dune stabilisation, in order to effectively control flooding. The coastlines in this area are typified by thin sands, and the mobile dunes, swept in by winds, often block river mouths and lead to flooding (Lubke & Hertling). Due to the stabilisation provided by the marrram Amophilia arenaria, indigenous fynbos species have been able to thrive, including Erhata villosa and Elymus distichus. Positive Oceanic Species Invasion The effect of mussel Mytilis galloprovincialis on the Cape region's waters has reached outside the mussel species into other ocean biodiversity, and most beneficially. Steffani and Branch (2004) observed that in regard to M galloprovincialis, Some of the species gain a substitute substratum on the mussels themselves, but only if they are small enough to live and reproduce on the mussels [] but (Mytilis galloprovincialis) has provided an additional source of food for higher predators, including the rare and endangered African Black Oystercatcher (Haematopus moquini). Therefore, the effect of the invasive mussel species is two-fold, in that it encroaches mussels on the western coast but may provide cause for the endangered Oystercatcher to succeed in an increasingly hostile habitat. Attempts to Control Species Invasion Alien species impacting and threatening the ecosystem in the South African cape, its land and waters, are extensive. Although multiple species of acacia have been introduced and are overtaking the area, bigger problems have been incurred than merely loss of habitat. Due to the complexity of alien species and their influences on native flora and fauna, investigations and attempts have been made to counteract the process. In the wake of so many invasive species on South African waters and land, it is of great importance to control the problem. Before the problem can be approached effectively, it has been necessary to define it. In 2004, a team of South African researchers (Nel, Richardson, Rouget, Mgidi, Mdzeke, Le Maire, van Wilden, Schonegevel, Henderson & Neser) proposed a classification procedure for invasive species. Their desire to this was to combat not only the most invasive species, but the emerging species as well. They attempted this with the hopes that while programmes must combat the most-invasive of plants and animals having impacted the region, work must also be done to combat the emerging invasive species which will be most threatening in the future. The importance for control is great. The Southern Cape region is unique in its biodiversity, with the majority of species therein endemic and in needing of protection. In New Scientist, Kate de Selincourt explained the beauty of the area, The southern tip of Africa boasts a remarkable natural relic: a rich ecological community that has enjoyed hundreds of thousands of years of relatively undisturbed evolution. Known locally as the fynbos ('fine bush'), it comprises an astonishing variety of trees, evergreen shrubs, insects and other animals, thousands of which occur nowhere else in the world. In the oceans, the mussel Scutellastra argenvillei threatens the native habitat of the mussel Perna perna. This encroachment on its habitat has been more easily defended on the southern coasts, concerning the mussel Mytilis galloprovincialis. On land, there has been some conservation achieved by the introduction of Marram grasses. The intention had been to provide stabilisation to the normal function of mobile sand dunes that clogged river mouths and flooded plains, hindering agricultural production and human establishment. It could be argued, however, that just like acacias, Marram grasses are equally problematic for particular animal species, namely the bird Black Harriet Circus maurus, whose nesting habitat is diminished. It has been difficult to control the proliferation of Marram grasses and acacias alike. However, some interesting methods have been undertaken with this aim. For example, Neser and Prinsloo (2004) identified after searching natural enemies of certain invasive acacias, three Bruchophagus wasps - naturally enemies for their seed-eating practises. In short, the attempts to combat the diminished biodiversity of the South African fynbos are complex. It is a difficult undertaking, but will need to be continued. Bibliography Baars, J. R. (2003) Geographic range, impact, and parasitism of lepidopteran species associated with the invasive weed Lantana camara in South Africa. Biological Control, 28 (3): 293-301. Branch et al. (2005). Two Oceans: a guide to the marine life of Southern Africa. Capetown: David Phillip. Brownes, S. J. & McQuaid, C. D. (2006) Will the invasive mussel Mytilus galloprovincialis Lamark replace the indigenous Perna perna L. on the south coast of South Africa Journal of Experimental Marine Biology & Ecology, 338 (1): 140-151. De Neergaard, A., Saarnak, C., Hill, T., Khanyile, M., Martinez Berzosa., A., & Birch-Thomsen, T. (2005) Australian wattle species in the Drakensberg region of South Africa - An invasive alien or a natural resource Agricultural Systems, 85 (3): 216-233. De Selincourt, K. (1992). South Africa's other bush war: Immigrant plants are sweeping through the Cape of Africa, threatening to strangle the region's prized bush vegetation. New Scientist, 1808, [Online retrieval]. Lubke, R. A. & Herling, U. M. (2001) The role of European marram grass in dune stabilization and succession near Cape Agulhas, South Africa. Journal of Coastal Conservation, 7 (2): 171-182. Nel, J. L., Richardson, D. M., Rouget, M., Mgidi, T. N., Mdzeke, N., Le Maitre, D. C., van Wilgen, B. W., Schonegevel, L., Henderson, L., & Neser, S. (2004) A proposed classification of invasive alien plant species in South Africa: towards prioritizing species and areas for management action. South African Journal of Science, 100 (1-2): 53-64. Neser, O. C. & Prinsloo, G. L. (2004) Seed-feeding species of Bruchophagus Ashmead (Hymenoptera: Eurytomidae) associated with native Australian acacias that are invasive in South Africa, with the description of two new species. Australian Journal of Entymology, 43 (1): 46-56. Odette, C., Simmons, R. E., & Jenkins, A. R. (2004). Black Harrier Circus maurus of the Fynbos biome, South Africa: a threatened specialist or an adaptable survivor Bird Conservation International, 14, 233-245. Ruis, M. & McQuaid, C. D. (2006). Wave action and competitive interaction between the invasive mussel Mytilus galloprovincialis and the indigenous Perna perna in South Africa. Marine Biology, 150 (1): 69-78. Manning, J. (2004). First field guide to fynbos of Southern Africa. South Africa : Struik. Mehta, S. (2000). The Invasion of South African Fynbos by an Australian Immigrant: The story of Acacia saligna. Retrieved 06 November 2006, from http://horticulture.coafes.umn.edu/vd/h5015/00papers/mehta.htm. Peschack, T. (2005). Currents of Contrast: Life in Southern Africa's Two Oceans. South Africa: Struik. Steffani, C. N. & Branch, G. M. (2004). Can we predict the effects of alien species A case-history of the invasion of South Africa by Mytilus galloprovincialis (Lamark). Journal of Experimental Marine Biology and Ecology, 340 (1-2):189-215. Steffani, C. N. & Branch, G. M. (2005). Mechanisms and consequences of competition between an alien mussel, Mytilus galloprovincialis, and an indigenous limpet, Scutellastra argenvillei. Journal of Experimental Marine Biology and Ecology, 317 (2): 127-142. Thuiller, W., Richardson, D. M., Rouget, M., Proches, S., & Wilson, J. R. (2006). Interactions between environment, species traits, and human uses describe patterns of plant invasions. Ecology, 87 (7): 1755-1769. Read More