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.

6. Zhou, K., Li, Y., Nishiwaki, M. & Kataoka, T. (1982). A brief report on observations of the baiji (Lipotes vexillifer) in the lower reaches of the Yangtze River between Nanjing and Guichi. Acta Theriol. Sin. 2, 253–254.

7. Zhang, X., Wang, D., Liu, R., Wei, Z., Hua, Y., Wang, Y., Chen, Z. & Wang, L. (2003). The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China. Aquat. Conserv. Mar. Freshw. Ecosyst. 13, 51–64.

8.Wang, D., Zhang, X., Wang, K., Wei, Z., Würsig, B., Braulik, G. & Ellis, S. (2006). Conservation of the Baiji: No Simple Solution. Conservation Biology. 20(3), 623-625.

9. Isaac, N.J.B., Turvey, S.T., Collen, B., Waterman, C. & Baillie, J.E.M. (2007). Mammals on the EDGE: conservation priorities based on threat and phylogeny. PLoS ONE.2(3), e296.

10. James, D. (2003). Limassol Link Photo Gallery. [Date Accessed: 01/12/10: http://www.limassollink.com/4images/details.php?image_id=864]

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.