Evolutionary Responses of Natives to Introduced Species.

The evolutionary responses of many native species to the introduction and invasion of non-native species whether they be plant or animal are often overlooked. This may be because when an introduced species becomes established in an area it seems to totally desimate the native population with no orvert defense shown by the native species. But infact there are many defense responses by native species,the most common responses include altered anti-predator defenses, changes in the spectrum of resources and habitats used, and other adaptations that allow native populations to persist in invaded areas (Carroll, et al 2006).

Just how well a native population can evolutionarily respond to the introduction of non-native species depends on just how aggressive the introduced species is, the genetic makeup for the native species, history of previous non-native invasions and the genetic variabilty of the native population. If there is a strong degree of variability within the native species it gives them a much greater chance of maintaining their population numbers. In a small number of cases where there is low genetic viarability and there has been previous invasions that caused serious limitations to the populations of native species, these native species willnatives will fail to evolve or otherwise adapt, and local or global extinction will result.

In other cases, adaptive change in natives may diminish impacts of invaders and potentially promote coexistence between invaders and natives (Carroll, et al 2006). Understanding the evolutionary component of non-native/ native species interactions is invaluable to showing the long-term impacts of invasions, and to understanding the role of evolutionary processes in the assembly and dynamics of natural communities.

References:

S.P. Carroll, J.A. Lau, S.Y. Strauss. (2006) Evolutionary Responses of Natives to Introduced Species: What do Introductions Tell us About Natural Communities. Ecology Letters. Vol. 9 pg. 375 - 374.

Cryptostegia grandiflora (Rubber Vine): An Invasive Weed.

Cryptostegia grandiflora or as it is commonly know the rubber vine, is a woody-perennial vine that is native to the southern regions of Madagascar. The rubber vine has become a significant weed in northern Australia, with some environmentalists regarding it as the one of, if not the worst weed in Australia at present. It has been introduced into many other tropical and subtropical regions as a ornamental plant because of its attractive flowers and because of the commercial quality natural latex rubber found in the sap of the vine (McFadyen & Marohasy, 1990).

Since its introduction into Northern Australia in 1917, rubber vine has spread to an excess of 30,00km²  of tropical Queensland. From the initial infestations alongside rivers, dense impenetrable thickets have become established, these tickets can cover trees up to 30m tall and can choke out all the native vegetation, it then progressively invades the surrounding areas (McFadyen & Harvey, 1990).

            Rubber vine in bloom (www.devereuxgardens.com).  Assessed on the 23rd of March 2014.                                           

Another one of the reasons why rubber vine is so devastating to Australia's native environment is its extreme toxicity. Less than 10g of rubber vine leaves can kill a 400kg horse within 6 days. It is highly toxic to sheep, cattle and goats. It has an unpalatable taste but during the dry season when grass is scarce many animals turn to the rubber vine as a last resort and as a consequence many perish. This can have a major effect on the lively hoods of cattle farmers with rubber vines on their properties (Land Protection, QDNRME 2004).

    Infestation of rubber vine in north Queensland (daff.qld.gov.au).Assessed on the 23rd of March 2014.

The highly specific rust fungus Maravalia crypto-stegiae was released during the summers of 1993-1994 by Lands Department and in 1994-1995 by the Queensland Department of Natural Resources. Long-term monitoring sites established in 1997 to evaluate the efficacy of the rust. At al the sites, there has been at least a 40% reduction in the number of live plants and stems per hectare, more than a 10% reduction in the number of live stems per plant and a significant reduction in seedling recruitment from 178 hectares to almost 0 in 2001(Lindsay & Vogler, 2002).

References:

•  R. E. McFadyen, J. J. Marohasy, 1990. A leaf feeding moth,Euclasta whalleyi (Lep.: Pyralidae) for the biological control of Cryptostegia grandiflora (Asclepiadaceae) in Queensland, Australia. Entomophaga 1990, Volume 35, Issue 3, pp 431-435
• R. E. McFadyen, G. E. Harvey, 1990. Distribution and Control of Rubber Vine, Crypotostegia grandiflora, a major weed in northern Queensland. Plant Protection Quarterly, 1990 Vol. 5 No. 4 pp. 152 - 155.
• Land Protection, Queensland Department of Natural Resources, Mines and Energy. Rubber Vine Management  March 2004.
• A. Lindsay, W. Vogler, 2002. "The impact of the rust fungus Maravalia cryptostegiae on three rubber vine (Cryptostegia grandiflora) populations in tropical Queensland." 13th Australian weeds conference ‘‘Threats now and forever. 2002.

Are Invasive Species The Drivers or Passengers in Environmental Change?

Invasive species can have significant effects on resource availability and can suppress or enhance the relative abundance of native species, without necessarily being the driving force behind community change (Didham, et al. 2005). 

It is now accepted that invasive species are one of the leading causes in world biodiversity loss, it has been assumed that the reasoning behind this domination is there ability to move into a degraded area or system and take advantage of the already imposed decline of the natural species within the affected  area. But another plausible hypothesis has come to light; can exotic species dominance be the indirect consequence of habitat modification, driving natural species loss (Didham, et al. 2005).

In a paper by MacDougall and Turkington, they have created the first direct test of whether invasive species are drivers of community change or just passengers along for the ride. The 'driver' model predicts that invaded communities are highly interactive, with subordinate native species being limited or excluded by competition from exotic dominants. 
The 'passenger' model predicts that invaded communities are primarily structured by non-interactive factors (environmental changes, dispersal limitation) that are less containing on the exotics, thus they dominate (MacDougall and Turkington, 2004). 

Species threatened by invasive species with New South Wales. Source: spa.nsw.gov.au. Assessed on the 13th of April 2014.

In order to prove this theory an area of oak savanna with different species of grass cover was located and the scientists then manipulated the weather conditions, soil condition and soil depth, grass species removal to see if the invasive species had an easier time adapting to these changes compared with the native species. The results of this testing showed that 36 of the 79 of native species did not respond to the treatments and declined. Seed numbers revealed that some of the species were dispersal limited and competition alone could not explain their rarity (MacDougall and Turkington, 2004). The results of MacDougall and Turkington's work show a lean towards the passenger model as the major cause of invasive species dominance, although the effects of the driver model on the ecological community was still quite substantial.

References: 

• MacDougall, A.S. and Turkington, R. (2005) Are invasive species the drivers or passengers of change in degraded ecosystems? Ecology 86, 42–55.
• Didham, R.K., Ewers, R.M., Gemmell, N.J., Hutchison, M.A., Tylianakis, J.M. (2005) Are Invasive Species the drivers of ecological change? Trends in Ecology and Evolution. Vol.20 No.9. 470 - 475.

Invasive Species: Just what exactly is an Invasive Species?

Invasive alien species are all organisms, animals, or plants that have a negative effect on “the local ecosystem and species” because humans have introduced them to an area that is outside of “their natural range,” and they then establish themselves and become broadly distributed in these areas. (Encyclopedia of Science and Technology Communication, 2010).

Cane toad (Bufo marinus) an extremely invasive pest species. Source: environment.gov.au. Assessed on the 13th of April 2014.

This basically means an introduced species is any organism that has been placed into an area that is not equip to sustain it without any negative effects of the native or original species of that area. These invasive species used up all the resources within the area, putting the native species at a disadvantage and eventually forcing them out of the area either by forcing them into extinction or causing them to move out of the area.
Invasive species generally have a higher rate of fecundity or in simpler terms, invasive species have a great rate of reproduction; producing more offspring than the native species and thus creating a population imbalance between the invasive species and the native ones.

The potential and actual distribution of the cane toad in Australia. Source: environment.gov.au. Assessed on the 13th of April 2014.

Most invasive species have either been intentionally or accidentally introduced into new areas by humans. Some invasive species were introduced into new areas in the hopes of decreasing the numbers of organisms that are affecting human livelihoods. An example of this is the  Cane Toad (Rhinella marina), the cane toad was released in small numbers around the cane farms located in Gordonvale, Queensland Australia. It was released in the hopes of controlling native grey-backed cane beetle (Dermolepida albohirtum) and French beetle (Lepidiota frenchi) (Clarke, G, et al 2000). This plan unfortunately backfired for the scientists involved, as the Cane Toads weren't all that interested in eating the beetles and could not jump high enough to reach the beetles located high up on the sugar cane. Instead the cane toads ate anything and everything else, with a high reproduction rate soon their populations skyrocketed out of control and spread throughout the rest of Cairns and soon throughout the rest of Queensland and beyond.

References:

• Clarke, G. M., Gross, S., Matthews, M., Catling, P. C., Baker, B., Hewitt, C. L., Crowther, D., & Saddler, S. R. 2000, Environmental Pest Species in Australia, Australia: State of the Environment, Second Technical Paper Series (Biodiversity), Department of the Environment and Heritage, Canberra.
• 2010. Encyclopedia of Science and Technology Communication. 1 Edition. SAGE Publications, Inc. Accessed on the 8th of March 2014.

The Start of a Beautiful Friendship.

Greetings fellow patrons of the interwebs.

I have created this blog in the hopes of presenting journal articles about the influence of invasive pest species on ecosystems and communities in a bit more of a user friendly way.

Cutting through the scientific jargon that can make journal articles hard to follow, to the good stuff. The amazing research done by scientists from all over the world.

Every week this blog will be updated with a new journal article relating to the influences of invasive pest species on the world around them. With me adding my two cents worth by either discussing what the journal article was about in laymans terms or maybe just explaining and describing some of the methods used by the authors of the articles to achieve their results.

Anyway enough about what is going to happen lets get this show on the road!