Monday, 5 March 2012

Modelling the effects of climate change on maize crops

I recently had to create a model using the software package STELLA. I decided to create a model which could predict the effects of climate change on maize production in sub-Saharan Africa. Maize is a fundamental crop in sub-Saharan Africa, accounting for 25% of the continent's staple food consumption and providing livelihoods. Studies have previously shown that maize growth is severely limited by high temperatures and low rainfall.

It is predicted that temperature will rise by 3°C and rainfall could decrease by up to 40% in Africa by 2050. Inputting these climatic changes into my model resulted in a 23% fall in the yield, when compared to optimum conditions.

A model such as this could be used to develop evidence-based policy in the management of agriculture. It would enable governments, charities and international organisations to foresee the effects of climate change on crop production, and therefore put the appropriate management strategies in place to offset the consequences. 

I found this project very interesting, and it enlightened me with regards to how useful modelling can be in research. I imagine as modelling software and techniques improve, statistical modelling will become a major aspect of scientific research. 

Wednesday, 30 November 2011

New Project: Comparative test of two conflicting metabolic scaling theories

My apologies for the lack of posts recently, but unfortunately I've had so much to do that I kind of fell out of the habit of updating my blog. I will endeavour to post more frequently from now on! I began a masters in September and have since begun work on my new research project, for which my supervisor is Dr David Atkinson. Here is a brief summary of my project:

Metabolism provides a crucial foundation to all biological processes, consequently meaning that theories which describe the rate at which metabolic rate scales with body mass could have great predictive power in ecology. There are currently scientific groups trying to predict this variation and determine the scaling relationship for species across wide ranges of taxonomic groups. This has led to the emergence of two main groups of competing theories; the first focussing on surface area and the second on transportation “networks”. Both groups of theories predict differing slopes when size increase is equal in three dimensions compared to when size increase is in two dimensions only (or in some dimensions more than others such that surface area remains directly proportional to body mass). This study will attempt to resolve some of this conflict and provide a powerful test of the competing metabolic scaling theories by collating extensive data from scientific literature to examine the relationship between metabolic rate and “shape” across a wide range of marine invertebrate taxa.  

It sounds a little daunting at first, but it is actually incredibly interesting! There is huge potential for this type of theory in the field of ecology, so if my project manages to distinguish between the different theories and determine which (if any!) is a more accurate representation of the truth, then it will (I hope) be a great success. I aim to have completed the data analysis by February, so I will keep you updated on the results! For now, I should get back to the endless task of data crunching..

Honey, I shrunk the animals!

Study warns that many species are shrinking as a result of climate change. Scientists predict damaging consequences that will impact ecosystems and human livelihoods across the globe.

It is now widely accepted that climate change presents a significant threat to the Earth’s ecosystems. Over the last 100 years, the planet has experienced a 1°C rise in temperature, and a further 7°C rise is predicted by 21001. A large amount of climate change research has been concentrated on distribution and behaviour shifts in species, however, more recently efforts have shifted towards the effects on growth and development2.

The study from Professor Bickford and Dr Sheridan (National University of Singapore)2 highlights the growing amount of evidence which describes the effect of climate change on species size. Species are exhibiting smaller sizes and slower growth rates in response to increased temperature and higher rainfall variability. 

The evidence for this shrinking effect is extensive. Fossil records have demonstrated similar effects in previous periods of global warming, where both marine and terrestrial species decreased in size2. Most notably during the warming phase of the Paleocene-Eocene Thermal Maximum (PETM), evidence shows a range of soil-burrowing invertebrates decreasing in size by 50-75%3. During the PETM temperatures increased by 3-7°C and rainfall decreased by 40%, so there is scope for comparisons as this is similar to the current predictions for the next 100 years2. Current climate change, however, is occurring at a much faster rate than during the PETM, so shrinkage effects may be accelerated3.

Experimental and comparative studies show that organisms across many taxa are smaller when they are exposed to conditions akin to climate change. For instance, considerable growth rate reductions have been observed in species as a result of water acidification (a consequence of increased atmospheric carbon dioxide)2. Red algae mass exhibit a 250% loss under acidic conditions4 and calcifying organisms such as corals become smaller and can even lose their ability to form exoskeletons5. Researchers have discovered that for a range of plant species, each degree of temperature increase can reduce the aboveground biomass by 3-17%6. Further comparative studies have also demonstrated that decreased rainfall can lead to species shrinkage in tropical trees7, mammals8 and amphibians9.

In addition to this, an increasing number of observational studies show that anthropogenic climate change over the last century has already caused species shrinkage. This is true of several mammals (including polar bears10, red deer11 and woodrats12) and birds (including passerines13 and gulls14) in response to increased temperature, and of many reptiles (Including tortoises15 and iguanas16) in response to decreased rainfall. Plant species show a decrease in size in response to both increased temperature and decreased rainfall, thus meaning that trees and plants are getting smaller in areas that are becoming drier and warmer17.

Scientists have suggested several explanations for species shrinking; however Sheridan & Bickford (2011)1 suggest that water and nutrient limitation and changes in metabolic rate of ectotherms are the most significant factors. Soil nutrients can decrease as regions become drier (more fires lead to nitrogen loss) and wetter (nutrient leaching), and decreased rainfall leads to reduced respiration. This can limit plant growth; effects which can cascade through a food web and disrupt the ecosystem. Metabolic rate is proportional to temperature18, thus growth is limited unless an organism can meet its metabolic needs at increased temperatures. An extensive range of species will be subject to these effects if they are not able to rapidly adapt to climate change. Natural selection favours smaller individuals in these conditions, which could eventually lead to the evolution of smaller species2.

Trends in the shrinking of species are variable and difficult to predict. It is thought that the biggest dilemma will be the differential responses amongst species, as this could disrupt the balance of whole ecosystems and have synergistic negative impacts on biodiversity2. One concern is that if producers shrink at a quicker rate than consumers, this will put pressure on the consumers and could lead to increased mortality, disease susceptibility and reduced reproductive output. Such effects could destabilize ecosystem interactions and threaten populations2. Also, organisms with shorter generation times may be more resilient to climate change, as they are able to adapt more quickly than those with longer generation times, creating further ecosystem disparity17.

A major threat to species is extinction and thus loss of biodiversity. Species with narrow temperature tolerance and/or low population levels are the most susceptible2. Amphibians and other ectotherms which become smaller to offset the effects of increased metabolism might become more susceptible to dessication2.

Marine systems are also likely to be severely affected, particularly because of varied rates of response to climate change which could destabilize ecosystems2. For instance, calcifying organisms have exhibited differing responses to acidification.

Studies have shown that clams and oysters decrease in size, whilst lobsters and crabs increase19.  Furthermore, warmer waters cannot hold as much dissolved oxygen, so organisms will encounter metabolic challenges2.

The impact of shrinkage on human livelihoods across the globe is arguably the most worrying consequence of species shrinkage. Fish stocks are expected to decrease in size and number owing to climate change, and this will impact the 1 billion people who rely on fish as their primary food resource20. Crops on land will also be affected as areas become drier or as rainfall variability increases, potentially reducing the length of growth seasons21. This will place a huge strain on countries which depend on crops to feed the population. Water limitation is also expected to be a severe issue in areas such as South Asia, where population growth rates are exploding21.

The consequences of species shrinkage are potentially widespread and devastating, and the publication of this study has rightfully attracted the attention of scientists, media and the public. We must now work together to fully understand this issue and put in place steps to reduce the potential damage to humans and animals alike. 

1.     IPCC Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) (Cambridge Univ. Press, 2007).
2.     Sheridan, J.A. & Bickford, D. (2011). Shrinking body size as an ecological response to climate change. Nature. DOI: 10.1038/nclimate1259
3.     Smith, J. J., Hasiotis, S. T., Kraus, M. J. & Woody, D. T. (2009). Transient dwarfism of soil fauna during the Paleocene–Eocene Thermal Maximum. Proc. Natl Acad. Sci. USA. 106, 17655–17660.
4.     Jokiel, P. L. et al. (2008). Ocean acidification and calcifying reef organisms: a mesocosm investigation. Coral Reefs. 27, 473–483.
5.     Ries, J. B., Cohen, A. L. & McCorkle, D. C. (2009). Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37, 1131–1134.
6.     Hovenden, M. J. et al. (2008). Warming and elevated CO2 affect the relationship between seed mass, germinability and seedling growth in Austrodanthonia caespitosa, a dominant      Australian grass. Glob. Change Biol. 14, 1633–1641.
7.     Parolin, P., Lucas, C., Piedade, M. T. F. & Wittmann, F. (2010). Drought responses of flood-tolerant trees in Amazonian floodplains. Ann. Bot. 105, 129–139.
8.     Yom-Tov, Y. & Geffen, E. (2006). Geographic variation in body size: the effects of ambient temperature and precipitation. Oecologia 148, 213–218.
9.     Brady, L. D. & Griffiths, R. A. (2000). Developmental responses to pond desiccation in tadpoles of the British anuran amphibians (Bufo bufo, B. calamita and Rana temporaria). J. Zool. 252, 61–69.
10.  Regehr, E. V., Amstrup, S. C. & Stirling, I. Polar Bear Population Status in the Southern Beaufort Sea Open-File Report 2006–1337 (US Geological Survey, 2006).
11.  Post, E., Stenseth, N. C., Langvatn, R. & Fromentin, J. M. (1997). Global climate change and phenotypic variation among red deer cohorts. Proc. R. Soc. Lond. B. 264, 1317–1324.
12.  Smith, F. A., Browning, H. & Shepherd, U. L. (1998). The influence of climate change on the body mass of woodrats Neotoma in an arid region of New Mexico, USA. Ecography 21, 140–148.
13.  Gardner, J. L., Heinsohn, R. & Joseph, L. Shifting latitudinal clines in avian body size correlate with global warming in Australian passerines. (2009). Proc. R. Soc. B 276, 3845–3852.
14.  Teplitsky, C., Mills, J. A., Alho, J. S., Yarrall, J. W. & Merila, J. (2008). Bergmann’s rule and climate change revisited: Disentangling environmental and genetic responses in a wild bird population. Proc. Natl Acad. Sci. USA 105, 13492–13496.
15.   Loehr, V. J. T., Hofmeyr, M. D. & Henen, B. T. (2007). Growing and shrinking in the smallest tortoise, Homopus signatus signatus: the importance of rain. Oecologia 153, 479–488.
16.  Wikelski, M. & Thom, C. (2000). Marine iguanas shrink to survive El Niño. Nature 403, 37–38.
17.  Franks, S. J. & Weis, A. E. (2008). A change in climate causes rapid evolution of multiple life-history traits and their interactions in an annual plant. J. Evol. Biol. 21, 1321–1334.
18.  Gillooly, J. F., Brown, J. H., West, G. B., Savage, V. M. & Charnov, E. L. (2001). Effects of size and temperature on metabolic rate. Science 293, 2248–2251.
19.  Vincent, G., de Foresta, H. & Mulia, R. (2009). Co-occurring tree species show contrasting sensitivity to ENSO-related droughts in planted dipterocarp forests.Forest Ecol. Manage. 258, 1316–1322 .
20.  Daufresne, M., Lengfellner, K. & Sommer, U. (2009). Global warming benefits the small in aquatic ecosystems. Proc. Natl Acad. Sci. USA. 106, 12788–12793.
21.  United Nations. (2009). Food and Agriculture Organization How to Feed the World in 2050. UN. [date accessed: 26/10/11].
22.  Bryant, D. (2011). Marine Wildlife Photography: Fish Schools. Seapics. [date accessed: 26/10/11]
23.  Seaggreen, D. (2010). A field of dried crops due to drought in Monduli District in Tanzania. Michigan State University. [date accessed: 29/10/11]

Thursday, 24 March 2011

The hourglass dolphin

Fig. 1   The hourglass dolphin (Tidman, 2011)

Common name: Hourglass dolphin              
Latin name: Lagenorhynchus cruciger (Quoy & Gaimard, 1824)

Cruciger is Latin for “cross-bearing” and denotes the area of black and white pigmentation on the back of the dolphin which when viewed from above, resembles an hourglass (Brownell & Donahue, 1999).

Kingdom:          Animalia
Phylum:            Chordata
Class:               Mammalia
Order:              Cetacea
Family:             Delphinidae
Genus:             Lagenorhynchus

Size and Weight
Adult length:
Male: 1.63m long (Nichols, 1908)
Female: 1.66m - 1.83m long (Fraser 1966)

There is possibly sexual dimorphism in the Hourglass dolphins, as male specimens are usually slightly shorter in length. However this is disputed to some extent due to a limited number of specimens (Brownell & Donahue, 1999).

Adult weight:
90-120 kg (Miyazaki, 1986)
The small and robust hourglass dolphin has inherited the nickname the “sea cow” due to its characteristic black and white colouring (Brownell & Donahue, 1999). The common name refers to the two white patches connected by a thin white strip on each flank, which bear a resemblance to an hourglass (Brownell & Donahue, 1999). Despite the species having no known predators, the hourglass dolphin exhibits counter-shading colouration (Brownell & Donahue, 1999). Countershading is an anti-predator defence where the belly is light in colour (blending with the light sky when viewed from below) and the back is dark in colour (blending with the dark depths when viewed from above) (Oxford Dictionaries, 2010).

The fin varies significantly between individuals, but it is generally tall and curved (Brownell & Donahue, 1999). It is thought that the curve is perhaps more pronounced in older individuals (Fraser 1966). The hourglass dolphin is easily distinguished from its similarly sized neighbour, the southern right whale dolphin (Lissodelphis peronii), as unlike the right whale, it has a dorsal fin (Brownell & Donahue, 1999).

The hourglass dolphin has a circumpolar distribution, in the higher latitudes of the southern oceans (Goodall, 1997; Goodall et al, 1997; Brownell & Donahue, 1999).

Fig. 2   Hourglass dolphin distribution, dominating the cold waters of 
the Southern Hemisphere (Hammond et al, 2008).

The southern range is to the Antarctic ice-edges, with the most southerly sightings occurring near 68°S in the South Pacific (Goodall 1997; Brownell & Donahue, 1999). The distribution in the north is less well known, however they are found to at least 45°S. Some sightings have occurred as far north as 36°S in the South Atlantic Ocean and 33°S near the Chilean city of Valparaíso (Goodall, 1997).

Hourglass dolphins are most commonly seen around the Antarctic Convergence or between South America and Macquarie Island (Goodall, 1997). They can also be seen off the south coast of New Zealand, near the South Shetland Islands and around the Tierra del Fuego province (Goodall, 1997). The hourglass dolphin is the only small delphinid species which is regularly found south of the Antarctic Convergence (Goodall et al, 1997). Hourglass dolphins are usually found in southern waters during the summer and northern waters during the winter, this suggests that they migrate seasonally following the cold-water currents (Goodall, 1997).

The hourglass dolphin is found in the cold, deep waters of the Antarctic; however some sightings have occurred in relatively shallow waters near South America and the Antarctic Peninsula (Goodall, 1997). It can be found within 160km of the ice edge within the Southern range (Jefferson et al, 1993). It appears to have a preference for surface water temperatures of between 0.6°C and -13°C (Goodall, 1997), but can even inhabit waters as cold as -0.3°C (Goodall, 2002).

Hourglass dolphins are sociable and usually observed travelling in small groups of around 7 individuals (Kasamatsu et al, 1990). Group sizes, however, can range from 1 to 100 individuals (Kasamatsu et al, 1990). The ratio of males to females within these groups is unknown; however it is unusual to see a calf travelling with larger groups (Kasamatsu et al, 1990). It has been suggested that this could be due to ship evasion from females with calves, or perhaps the species undergoes synchronised breeding in the winter (Kasamatsu et al, 1990). There is a lack of information with regards to the parental care behaviour exhibited in the species, however, we do know that females nurse their young from birth and based on data from other species in the genus, it is thought that lactation lasts for 12-18 months (Brownell& Donahue, 1999).

Hourglass dolphins enjoy riding bow waves and wakes, and have been observed altering their direction of travel just so they can catch the waves created by travelling boats and ships (Bowles et al, 1994). They also like to ride the bow waves of fin whales, Balaenoptera physalus, regularly jumping out of the water as they play around the larger animals (Fraser, 1964). Whalers historically searched for this characteristic behaviour in order to locate the fin whale in their hunt. Hourglass dolphins also like to socialise with other species such as the minke whale (Balaenoptera acutorostrata), pilot whales (Globicephala melas and Globicephala macrorhynchus), beaked whales (Ziphiidae), sei whale (Balaenoptera borealis) and southern right whale dolphins (Lissodelphis peronii) (Kasamatsu et al, 1988).
Fig. 3   Hourglass dolphins porpoising (Pitman, 2011)

Other areas of uncertainty include the lifespan of the hourglass dolphin; however it is likely to be comparable to that of other species within its genus (Brownell & Donahue, 1999). The closely related Atlantic white-sided dolphin (Lagenorhynchus acutus) has a lifespan of 27 years, whereas the Pacific white-sided dolphin (Lagenorhynchus obliquidens) can live to 46 years (Klinowska, 1991).

Little is known about the feeding habits of the hourglass dolphin, but scientists have recorded small fish, cetaceans and squid (from the Onychoteuthidae and Enoploteuthidae families) from the stomach contents of several specimens (Clarke, 1986; Ash 1962). The species has also been observed feeding in plankton swarms and seabird aggregations (Clarke, 1986).

Like all toothed whales, hourglass dolphins use echolocation for orientation and prey location (Khyn et al, 2009). It is also likely that they also communicate using visual and tactile cues (Brownell & Donahue, 1999). A recent study showed that they produce very high-pitched clicks, which allow them to detect prey at more than twice the distance of other dolphin species (Khyn et al, 2009). It was suggested that this could be due to the deep and open nature of their habitat, meaning that the hourglass dolphin needs to cover larger areas to locate prey (Khyn et al, 2009).

There are currently no known threats to the hourglass dolphin (Brownell & Donahue, 1999). In 1995, the first and only study to date (March, 2011) was conducted on the population size of the species, combining data from surveys occurring from 1976 to 1988. This study estimated that there were 144,300 individuals for waters south of the Antarctic convergence (Kasamatsu and Joyce, 1995).

It is thought that the species is probably preyed upon by killer whales, Orcinus orca, but there hasn’t been any documented evidence of predation. The hourglass dolphin is not commercially hunted and accidental by catch is limited (Brownell & Donahue, 1999).

The Hourglass dolphin is classified as Least Concern (LC) on the IUCN Red List (Hammond et al, 2010) and listed on Appendix II of CITES. There have been no attempts to bring the hourglass dolphin into captivity, apart from several specimens being collected for scientific research (Brownell & Donahue, 1999). This is most likely due to their remote distribution (Brownell & Donahue, 1999). Increasing ecotourism in the Antarctic will likely lead to further knowledge of this species (Brownell & Donahue, 1999).

Ash, C. (1962). “Whaler’s Eye”. Macmillan, New York.
Bowles, A.E., Smultea, M., Wursig, B., DeMaster, D.P. & Palka, D. (1994). Relative abundance and behaviour of marine mammals exposed to transmissions from the Heard Island Feasibility Test. J. Acoust. Soc. Am. 96 (4), 2469-2484.
Brownell Jr., R. L. and Donahue, M. A. (1999). Hourglass dolphin Lagenorhynchus cruciger (Quoy and Gaimard, 1824). In: S. H. Ridgway and R. Harrison (eds), Handbook of marine mammals, Vol. 6: The second book of dolphins and the porpoises. pp. 121-135. Academic Press, London.
Clarke, M.R. (1986). Cephalopods in the diet of odontocetes. In “Research on Dolphins”. (Eds M. M. Bryden and R. Harrison). pp 281-321. Clarendon Press, Oxford.
Fraser, F.C. (1964). Whales and whaling. In “Antarctic Research: A Review of British Scientific Achievement in Antarctica” (Eds R. Priestley, R.J. Adie and G. De Q Robin) pp 191-205. Butterworths, London. 
Fraser, F.C. (1966). Comments on the Delphinoidea. In “Whales, Dolphins and Porposies” (Ed. K.S. Norris), pp 1-31. University of California Press, Berkeley, CA.
Goodall, R. N. P. (1997). Review of sightings of the hourglass dolphin, Lagenorhynchus cruciger, in the South American sector of the Antarctic and the sub-Antarctic. Reports of the International Whaling Commission. 47, 1001-1014.
Goodall, R. N. P., Baker, A. N., Best, P. B., Meyer, M. & Miyazaki, N. (1997). On the biology of the hourglass dolphin, Lagenorhynchus cruciger (Quoy and Gaimard, 1824). Reports of the International Whaling Commission. 47, 985-999.
Goodall, R. N. P. (2002). Hourglass dolphin Lagenorhynchus cruciger. In: W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 583-585. Academic Press, San Diego, California, USA.
Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells,
R.S. & Wilson, B. (2008). Lagenorhynchus cruciger. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. []
Jefferson, T. A., Leatherwood, S. & Webber, M. A. (1993). Marine Mammals of the World: FAO Species Identification Guide. United Nation Environment Programme and Food and Agricultural Organization of the UN.
Kasamatsu, F. and Joyce, G. G. (1995). Current status of odontocetes in the Antarctic. Antarctic Science. 7, 365-379.
Kasamatsu, F., Hembree, D., Joyce, G. Tsunoda, L., Rowlett, R. & Nakano, T. (1988). Distribution of cetacean sightings in the Antarctic: results obtained from the IWC/IDCR minke whale assessment cruises, 1978/79 to 1983/84. Rep. Int. Whal. Commn. 38, 449-487.
Kasamatsu , F., Joyce, G., Ensor, P. & Mermoz. J. (1990). Current occurrence of cetacean in the Southern Hemisphere minke whale assessment cruises, 1978/79-1987/88. Paper SC/42/015 presented to the International Whaling Commision Scientific Commitee.
Klinowska, M. 1991. Dolphins, Porpoises and Whales of the World. The IUCN Red Data Book. Gland, Switzerland and Cambridge, U.K.
Kyhn, L.A., Tougaard, J., Jensen, F., Wahlberg, M., Stone, G., Yoshinaga, A., Beedholm, K. & Madsen, P.T. (2009). Feeding at a high pitch: Source parameters of narrow band high- frequency clicks from echolocating off-shore hourglass dolphins and coastal Hector’s dolphins.  J. Acoust. Soc. Am. 123 (3), 1783-1791.
Miyazaki, N. (1986). Catalogue of Marine Mammal Specimens. pp 151.National Science Museum, Tokyo.
Nichols, J.T. (1908). Notes on two porpoises captured on a voyage into the Pacific Ocean. Bull. Mus. Nat. Hist. NY. 25, 217-219.
Pitman, R.L. (2011). ARKive image. [].
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Monday, 13 December 2010

Humans cause new extinction record

A visual and acoustic survey of the Yangtze River dolphin (Lipotes vexillifer) confirms the first human-induced extinction of a large vertebrate species for over 50 years.

The Yangtze River dolphin (Fig.1), more commonly referred to as the baiji or the “Goddess of the Yangtze” is an obligate freshwater odontocete or toothed whale. Its distribution is exclusive to the middle-lower region of the Yangtze River, with records of sightings expanding into the neighbouring Qiantang River of eastern China.
The baiji has long been considered to be one of the rarest and most threatened mammal species on the planet, suffering from a rapid population decline. A recent study by Turvey et al1 failed to detect the presence of the baiji, using systematic visual and acoustic surveys ranging from Yichang to Shanghai (Fig.2). This has led to the unfortunate conclusion that the Yangtze River dolphin has most likely been driven to extinction.

Figure 1. The Yangtze River Dolphin/baiji (Lipotes vexillifer)10

In 2001, the IWC listed the baiji as the most endangered cetacean on the planet2. It previously occurred as far upstream as Tonglu in the Fuchun river3. Its distribution was gradually reduced from a 1000 mile stretch of the middle-lower Yangtze to just 150km of the main channel, as depicted in figure 2, between the tributary lakes of Dongting and Poyang4. Approximately 12% of the world’s human population live in the Yangtze region, and this has led to extreme ecological pressure and deterioration5. Habitat loss has been caused largely due to the construction of the three gorges dam, along with other small-scale damming developments.
There have been ongoing surveys documenting the dramatic decline of the baiji. The population declined from an estimated 400 in 19816 to 13 in 19997. The People’s Republic of China declared the baiji endangered in 1979, but only made baiji hunting illegal in 1983, by which point the population had already collapsed to just 300 individuals. Throughout this time, the development of dams led to severe habitat and species loss along the river, most notably by the Gezhouba Dam (1989) and the Three Gorges Dam (1994). The IUCN listed the species as critically endangered by 1996, with the last recorded sighting occurring in 2004. 
Figure 2. A map of the survey route from Turvey et al1
covering the historical distribution of the baiji in the main channel of the Yangtze River. 

Baiji fatalities have been somewhat attributable to direct injuries from entanglement in fishing gear (predominantly rolling hooks), electrocution from electric fishing, hunting, underwater blasting for channel maintenance and collisions with vessels. In addition to this, industrialisation has led to tributary damage, dredging, overfishing, vessel traffic and drainage for land reclamation, causing a severe ecological deterioration of the region5. It is believed that the primary cause of the baiji decline has been due to unsustainable by-catch in local fisheries, which employ damaging fishing practices. Despite legislation, these harmful unselective fishing techniques remain ubiquitous1.
There was a general consensus amongst scientists that the best management strategy would be to combine in-situ and ex-situ conservation efforts, in order to preserve the habitat as well as raise a large enough population to be re-introduced. Conservation strategies were implemented from the 1980s, with attempts to capture dolphins for relocation to reserves. These efforts, however, were largely unsuccessful as the capture of the quick dolphins proved to be difficult, and those that were caught had low captive survival rates. Five protected reserves were established along the Yangtze in 1992; however this covered just 1/3 of the baiji’s natural habitat range and had limited success8. It was very much a case of too little too late, and as August Pfluger of the Baiji Foundation said in 2006; “The strategy of the Chinese government was a good one, but we didn’t have time to put it into action”.
It is clear that anthropogenic factors have driven the baiji to extinction, and this threatens to have similar effects on other freshwater cetaceans, in particular the Yangtze finless porpoise (Neophocaena phocaenoides)5. The Chinese paddlefish (Psephurus gladius) is a sturgeon which is also at risk of extinction because of the Yangtze River deterioration7. However, this is a world-wide issue and some of the most critically endangered species on the planet are currently threatened because of unsustainable fishing practices (e.g. the Gulf of California porpoise, Phocoena sinus1). The Yangtze River dolphin was one of five freshwater dolphins on the planet. The remaining four are the Amazon River dolphin (Inia geoffrensis), the La Plata River dolphin (Pontoporia blainvillei), the Ganges River dolphin (Platanista gangetica) and the Indus River dolphin (Platanista minor). River dolphins, in particular the La Plata River dolphin are all at risk of extinction because of habitat loss and hunting9. The baiji represented the only recent species from the Lipotidae clade, having diverged from other cetacean lineages in excess of 20 million years ago9.
The Baiji extinction denotes a significant loss of mammalian evolutionary history. It marks the fourth disappearance of an entire mammal family since AD 1500, the first global extinction of a megafaunal vertebrate in half a century, the first species extinction of a charismatic vertebrate of conservation interest and the first cetacean species to have been driven to extinction by human activity. An impressive record, but for all the wrong reasons. The extinction of the remarkable Yangtze River dolphin serves as a crucial reminder that continuous conservation efforts and interventions remain pertinent if we are to sustain the biodiversity that we enjoy today.

1. Turvey, S.T., Pitmann, R.L., Taylor, B.L., Barlow, J., Akamatsu, T., Barrett, L.A., Zhao, X., Reeves, R.R., Stewart, B.S., Wang, K., Wei, Z., Zhang, X., Pusser, L.T., Richlen, M., Brandon, J.R. & Wang, D. (2007). First human-caused extinction of a cetacean species? Biol. Lett. 3, 537-540.
2. IWC. (2001). Report of the standing sub-committee on small cetaceans. Journal of Cetacean Research and Management. 3 (Supplement), 263–291.
3. Zhou, K., Qian, W., and Li, Y. 1977. Studies on the distribution of baiji, Lipotes vexillifer Miller. Acta Zoologica Sinica 23, 72–79. [In Chinese; English summary.]
4. Reeves, R.R., Smith, B.D., Crespo, E.A. & Notarbartolo di Sciara, G. (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World’s Cetaceans. IUCN/SSC Cetacean Specialist Group. IUCN, Glad, Switzerland and Cambridge, U.K.
5. Zhou, K., Sun, J., Gao, A. & Würsig, B. (1998). Baiji (Lipotes vexillifer) in the lower Yangtze River: movements, numbers threats and conservation needs. Aquat. Mamm. 24(2), 123–132.
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Wednesday, 1 December 2010

A relevant grand opening..

At risk of appearing like a beetle maniac, I decided to choose a beetle-related post to start with. As the British geneticist and evolutionary biologist J.B.S. Haldane said: "If the Creator exists, he had an inordinate fondness for beetles". This refers to the fact that the Coleoptera order contains more described species than any other order in the animal kingdom. Beetles constitute 25% of all known species, with an estimated 400,000 species in total.

Last year I went on a field trip to Uganda, spending part of my stay studying in Kibale forest. I carried out a study, focussing on the Dung Beetle (Scarabaeidae) preference for cow dung age and forest location. The dung beetle family display huge variation with 27,800 species worldwide, over 30 of which were identified in Kibale Forest by Nummelin & Hanski (1989). 

Dung beetles are characterised by modified forelimbs for digging, lamellate or clubbed antennae and a large head and pronotum. Strong competition over the high quality dung resource has led to specialization of the Scarabaeidae family. There are three classes of dung beetle, which use the dung in different ways: rollers; which make balls of dung and relocate them to hide in the soil, tunnellers; which build tunnels and nest under the dung, pushing it into chambers, and dwellers; which live and nest within the dung. They exhibit coprophagy; the ingestion of faeces. 

Dung beetles are of high ecological importance, as they decompose dung and other decaying organic matter and augment the processes of seed dispersal and nutrient recycling within ecosystems. They facilitate ecosystem growth by cleaning away dung, consequently reducing vector and disease. Despite the decomposition of dung occurring naturally; intensive farming methods lead to a large deposition of dung. This can cause environmental problems such as nutrient leaching and reduced pasture production because of increased forage fouling. Livestock will not graze in their excrement, thus reducing productivity. Dung beetles are consequently vital in agriculture, and enhance grazing quality by removing manure quickly and efficiently. 

Dung beetles can also be used as Biological control agents, and there have been several instances of introductions which have successfully increased productivity. They are regarded as a keystone species, exerting a large and stabilising influence throughout ecological communities and having a close relationship with the mammalian fauna. 

It is known that dung beetles are differentially adapted to utilize various types of dung, and where there are two or more large herbivorous species present; a niche dimension is observed. Studies into dung beetle use of different dung ages, however, are lacking, with little knowledge of how this differs in different environments. One would presume that new dung contains a higher concentration of nutrients and that the composition of dung breaks down more quickly in exposed secondary forest as opposed to the moist conditions within primary forest. It is clear that if dung is not recycled, nutrients are not put back into the ecosystem, thus decreasing the productivity. What needs to be made clear, however, is the potential effect on the ecosystem if the nutrients are not recycled by dung beetles. Concerns such as logging cause forest fragmentation, producing more secondary forest. If dung beetles are less active in secondary forest, does this mean there is a lower productivity? Would a buildup of dung affect plants? Perhaps it would prevent light access? This topic raises several questions which should be answered before decisions to continue to interfere with forests across the globe are made.

In light of this lack of knowledge, a project was designed to look at dung beetle activity across areas of primary and secondary forest within Kibale Forest. Kibale Forest is a moist evergreen forest in western Uganda (0° 27' N, 30° 26' E). There are two wet seasons; the first occurring between late August and early December and the second occurring from between early March and early May.  The annual rainfall is approximately 1500mm (Mahaney et al, 1997). It resides at a medium altitude of 1500m. The forest area is approximately 550km2, isolated from other areas of forest by approximately 50km.

A hypothesis was formed based around the question: Does the age and location of cow dung have an effect on the abundance and species diversity of dung beetles? We predicted that in the primary forest; the abundance and diversity would be higher due to the moist climate being “locked in” by the forest canopy. In addition to this, previous studies have shown dung beetles to have a preference for dark conditions. We also predicted the abundance and diversity to be higher for the new dung treatment as it would have a higher nutrient content, potency and preferred consistency. 

We found that Scarabaeidae abundance was significantly greater in areas of primary forest compared with felled secondary forest and on dung which has aged for shorter lengths of time (Figure 1). Probable reasons for this include the higher nutrient content, moistness and softer composition of younger dung. New dung is more useable and beneficial to dung beetles. This has implications in ecosystems where dung is more exposed to dry, hot and exposed conditions, allowing for the dung composition to change and “age” much more quickly. As well as this, the moist climate and dense canopy of the primary forest allow for the dung composition to change at a slower rate, retaining nutrients and moistness.  There is a clear preference for established primary forest, enabling nutrient recycling to occur at a faster rate. This suggests that in primary forest ecosystems that are reliant on dung beetles as principle nutrient recyclers, deforestation and fragmentation would have a detrimental effect on sustainability.

Figure 1. Effect of location and treatment on mean abundance (per pot) 
of dung beetles (Location: df=1, 21, F=6.77, P=0.018, Treatment: df=2, 21, F=16.92, P<0.001). Green represents primary forest, and black represents secondary forest.

Scarabaeidae species diversity, however, did not significantly differ across different ages of dung or across areas of primary and secondary forest (Figure 2). This suggests that both the age of dung and the ecosystem type has a larger effect on the abundance of beetles processing dung than on the diversity. It is, however, possible that due to the small sample size, the results were not entirely accurate, as a higher diversity of beetles was recorded on new dung and in primary forest, but the difference was not statistically significant. As most of the mammals in Kibale forest, use both primary forest and secondary felled forest, resources are largely available for dung beetles in both forest types. This could explain why a larger difference in species diversity wasn’t observed. The fact that the diversity data follows the same pattern to that of the abundance calls for further studies into this area to allow for a more concrete analysis.

 Figure 2. Effect of location and treatment on mean diversity index (per pot) 
of dung beetles (Location: df=1, 19, F=0.47, P=0.503, Treatment: df=1, 19, F=1.77, P=0.201). Green represents primary forest, and black represents secondary forest.

To conclude, this study further confirms the importance of dung beetles within ecosystems. There are potential implications of logging, which produces more secondary forest, on the abundance of dung beetles. This should be considered by organizations implementing forestry control, as long-term effects on productivity could be detrimental.