Banana Bunchy-Top Virus (BBTV)

Just what is the Banana Bunchy-Top Virus?

BBTV is a virus that affects the banana plants ability to produce leaves and petioles, this causes the plants 'bunched' look. Not only does it cause the plant to have a bunched look it also can distort the fruit, making it unsellable and cause the sterilisation of the plant, before eventually killing it (ISSG, BBTV. 2005). BBTV was first recognised in Fiji in 1889,since then it has spread worldwide and effects banana production. The virus can be spread from plant to plant by banana aphids, there are no resistant banana plant species. Controlling the spread of the virus is done through the destruction of affected plants, cessation of transportation of organic material from the affected area and pesticide use to eliminate the aphid species (Thomas and Dietzgen. 1991). Banana aphid can retain the virus for many weeks and because of this have this has the ability to cover large distances (DAAF, 2014). Scientists have cultured banana plant material from affected plants and have managed to produce material that does not contain the Bunchy-Top Virus (DAFF, 2014).

A healthy group of Banana plants.

Source:http://kccbigcountry.hubpages.com/hub/Banana-Tree, Accessed on the 29th of April 2014.

Within Australia BBTV is currently present in SE Queensland and Northern New South Wales. Do to strict quarantine measures within Australia concerning the transportation of possible infected organic materials it has not spread to other areas on Australia yet (DAFF, 2014).

The Affects of BBTV. 

Source: en.wikipedia.com, accessed on the 29th of April 2014. 

Because of it's ability to spread rather easily and the lack of progress in finding a 'cure' for this virus, the Banana Bunchy-Top Virus has become one of the world's most devastating plant viruses. In Australia BBTV is the focus of a 3 year project funded by the Australia Banana Growers Council, the Banana Industry Advisory Committee and Horticulture Australia Limited to work towards its eradication (DAFF, 2014). But in other parts of the world there has been little effort made to help find a permanent solution to this virus.

Banana Virus quarantine sign in Hawaii.

Source: http://great-hikes.com/blog/banana-virus/, accessed on the 29th of April 2014.

References:

Bunchy Top. (2014). Available at: http://www.daff.qld.gov.au/plants/health-pests-diseases/a-z-significant/bunchy-top. (Accessed 29th of April 2014).

Ecology of Banana Bunchy-Top Virus (BBTV) (2005). Available at: http://www.issg.org/database/species/ecology.asp?si=141. (Accessed 29th April 2014.)

Thomas, J, E,. and Dietzgen, R.G. (1991). Purification, characterisation and serological detection of virus-like particles associated with banana bunchy-top disease in Australia. Journal of General Virology 72: 217-224. University of Hawaii at Manoa.

Feral Cats (Felis catus) in Australia

The domestic cat (Felis catus) was first introduced into Australia in 1806 and by 1820 there were already significant numbers of feral cats surrounding Sydney, by 1890 90% of Australia had a feral population (Abbott, 2008). Cats are small carnivorous mammals that feed on small vertebrate and invertebrate animals. The introduction of cats to Australia had a profound effect on the small native wildlife. In the early part of the 20th century large populations of cats were released into gold mining sites in Western Australia, and as a form of population control for the rabbit and native rat (Dickman, 1996). This attempt at bio control caused for the populations of feral cats to increase tenfold and further affect the dwindling numbers of native birds and mammals within these areas.

Distribution of Feral Cats in Australia. Source: Feral.org.au, Assessed on the 13th of April 2014.

A major case study on the effect of feral cats on a species is the decline of the eastern barred bandicoot (Perameles gunnii) in Victoria, this population first started to decline in 1840 following settlement by Europeans who cleared land for grazing and introduced carnivorous species like the cat. By 1982 there was only a population of 1750 and as little as 150 by 1990. Scientists’’ believe that the introduction of feral cat species into the home range of the barred bandicoot increasing the mortality rate of the juveniles of the species thus causing the collapse of the population as a whole (Dickman, 1996).

 Feral Cat in the Northern Territory. Source: Tim Doherty ECU. Assessed on the 13th of April 2014.

Feral cats within Australia have no known natural predator except for the Wedge-tailed eagle and the dingo, without these two species managing the population numbers, feral cats are the apex predators. Cats have become one of the greatest threats for native wildlife survival in Australia and are now one of the worst invasive species to be introduced to this country.

References:

• Abbott, I. (2008). Origin and spread of the cat, Felis catis on mainland Australia. Conservation Science Western Australia Journal. Vol. 7, 1 – 17.
• Dickman, C. (1996). Overview of the Impacts of Feral Cats on Australian Native Fauna. Australian Nature Conservation Agency – Institute of Wildlife Research. Pg, 1 – 97.

Understanding the Long Term Effects of an Invasive Species.

The introduction of non-native species to an area can effect many of the processes that keep that area in balance this includes evolution, shifts in species composition, accumulation of materials and interactions with abiotic variables, these processes may increase,decrease, or qualitatively change the impacts of an invader through time (Strayer, et al. 2006). The effects of the non-native species change over time. With many scientists refering to the time directly after the non-natice species has taken ahold of a new environment as the 'acute' phase, the phase where the native species incur the most damage. This is then followed by a 'chronic' phase where various ecological and evolutionary processes come into play.

 The invasion curve of the long-term effects of invasive species.

Source: senrm.sa.gov.au. Assessed on the 13th of April 2014.

Invasive species have large effects on native biodiversity, cause hundreds of billions of dollars in economic damages, and complicate the management of natural ecosystems around the world, their effects are pervasive and varied, changing variables such as the genetics and population size of individual species, diversity and structure of communities, disturbance regimes and biogeochemical cycles (Strayer, et al. 2006).

Previous attempts to explain the ecological effects of an invader have focused on two attributes: its functional distinctiveness (i.e. how much its characteristics such as nitrogen fixation, flammability, phenology, chemical defenses and diet differ from those of species already in the community) and its abundance (Vitousek, 1990). The data collected in Strayer, 2006; shows that both evolutionary and ecological processes can change the abundance and function distinctiveness of a species over a period of time. This change allows for the native species to be able to slightly diminish the effects of the non-native species. This 'third' attribute (time) needs to be heavily considered when looking and understanding the long term effects of an introduced species.

The 4 main changes in an environment after the introduction of a non-native species are:
(1) Changes in the species that invades.
(2) Changes in the biological community that is invaded.
(3) Cumulative changes in the abiotic environment that is invaded.
(4) Interactions between the invading species and other variables that control the ecosystem.
(Strayer, et al. 2006)

A species can change through time by acclimatization, including shifts in gene expression, resource allocation, or morphology and physiology within the lifespan of an individual. Such changes can influence many community and ecosystem processes (Eviner and Chapin, 2003). After an invasive species arrives in a new region, evolution should tailor it to better fit the physicochemical environment and biota that it encounters, increasing its local population size and spread, and thereby its impacts (Strayer, et al. 2006). Predators, parasites, and diseases of the invader, for which the invader is a valuable resource, might arrive or proliferate to take advantage of the invader, thereby reducing its population size or distribution (Parker, et al. 1999). Analogous changes that moderate the impact of invaders can occur within the species of the community that is invaded, either as a result of genetic or phenotypic changes (Strayer, et al. 2006).

References:

Eviner, V.T. and Chapin, F.S. III (2003) Functional matrix: a conceptual framework for predicting multiple plant effects on ecosystem processes. Annu. Rev. Ecol. Syst. 34, 455–485.

Parker, I.M. et al. (1999) Impact: toward a framework for understanding the ecological effects of invaders. Biol. Inv. 1, 3–19.

Strayer, D.L., Eviner, V. T., Jeschke, J.M. & Pace, M.L. (2006) Understanding the Long-Term effects of Species Invasions. TRENDS in Ecology and Evolution. vol. 21, No. 11. pg. 645 - 651.

Vitousek, P.M. (1990) Biological invasions and ecosystem processes: towards an integration of population biology and ecosystem studies. Oikos 57, 7–13.