Opportunistic Torpor Down Under

Seasonal torpor is well known in northern latitudes. Placental mammals, including some rodents and many bat species, enter torpor to conserve energy when ambient temperatures fall and food becomes scarce. Prolonged torpor is characterized by highly Read More...

African Wild Dogs Fear Lions

There is no love lost between lions (Panthera leo)and African wild dogs (Lycaon pictus, Figure 1) on the plains or Africa. Lions often steal kills made by wild dogs and have been known to kill pups and occasionally adults. In fact, in the Moremi Game Reserve lions cause 47% of wild dog deaths according to Botswana researcher John McNutt. The need to avoid lion prides may be one of the reasons that wild dogs require such large home ranges.

    Steve Jurvetson
Figure 1. An African wild dog (Lycaon pictus). (From Steve Jurvetson/Flickr)

The hypothesis that threats from larger competitors like lions and hyenas limit wild dog population density and distribution has only recently been tested in the field. Hugh Webster, John McNutt, and Karen McComb played lion roars and hyena whoops to 8 packs of African wild dogs and observed their responses. The lion roars were from both male and female lions recorded in other African parks. These roars were presented as single lions roaring or as choruses of 3 lions roaring together. The hyena whoop calls were similarly recorded and presented to the wild dog packs.

Wild dog packs responded to lion roars by standing, facing the direction of the hidden speakers, rearing up on their hind legs to get a better view, and cautiously approaching the source of the roar. In dense habitats, however, the wild dogs quickly retreated (Figure 2).

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Figure 2. A bar chart showing the mean time to retreat by wild dog packs’ in response to lion roars in habitats of differing density. (Webster et al., 2012)

Wild dogs responded very differently to hyena whoops (Figure 3). Instead of retreating, wild dog packs generally remained in the same area and eventually dozed off, suggesting that hyenas in the area do not pose a significant threat to the pack.

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Figure 3. Wheel diagrams showing the direction and distance travelled by wild dog packs in the hour following playbacks of lion roars or hyena whoops. The playback loudspeaker is located 100 m north of this center point. (From Webster et al., 2012)

Interestingly, wild dog packs did not differ in their response when choruses of 3 lions were presented versus only a single lion roar. In fact, the only variable that explained wild dog behavior was the density of the surrounding habitat. Presumably, wild dogs are at greater risk of ambush by lions in dense vegetation where sight is limited.

These results indicate that lions may limit wild dog packs to areas on the periphery of lion ranges or to areas with less prey where the packs are less likely to encounter lions. As the authors point out, this has important implications for wild dog reintroduction programs. It may be best to avoid reintroductions in areas were lions are abundant.

References

Webster, H., McNutt, J., & McComb, K. (2012). African Wild Dogs as a Fugitive Species: Playback Experiments Investigate How Wild Dogs Respond to their Major Competitors Ethology, 118 (2), 147-156 DOI: 10.1111/j.1439-0310.2011.01992.x
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Evolution of Ancient Dugong Communities

Manatees and dugongs are puzzling creatures. They are large, slow-moving aquatic mammals that inhabit tropical and subtropical waters. They graze on aquatic vegetation in freshwater and shallow marine environments. Like cetaceans, the four living species of manatees and dugongs (Order Sirenia) have horizontal tail fluke in place of hind limbs and flipper-like forelimbs (Figure 1).

Christian Haugen
Figure 1. A living dugong from the Indo-Australian region (Dugong dugon). (From Christian Haugen/Flickr)

Today sirenians have disjunct and allopatric distributions. However, careful analysis of the fossil record reveals that ancient dugong communities were more diverse. Jorge Velez-Juarbe, Daryl Domning, and Nicholas Pyenson report in the journal
PLoS ONE that multispecies communities existed in many parts of the world until relatively recently (Figure 2).

dugong2
Figure 2. An illustration by Carl Buell showing the three species in each fossil dugongid assemblage. Multispecies communities are from Florida (top left), India (top right) and Mexico (bottom right) over the past 26 million years. (From Velez-Juarbe et al., 2012)


By evaluating a suite of ecomorphological characters including the size and shape of the upper tusk, the degree of downward deflection of the snout, and overall body size, the researcher constructed a phylogenetic tree of fossil sirenians. The tree revealed that late Oligocene dugongs from Florida differed in body size and tusk size (Figure 3). Likewise the early Miocene dugong assemblage from India consisted of three taxa with different degrees of skull deflection and two body size categories. The early Pliocene dugongs from Mexico differed in body size and tusk shape (cross-sectional shape).

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Figure 3. Ecomorphological features for the fossil taxa used in this study. A)
Categories of upper incisor size and depth (gray) for late Oligocene species from Florida B) body sizes comparisons among dugongids in this study. C) Fossil dugongids from India showing differences in rostral deflection. D) Cross-sectional outline of incisors of fossil dugongids from Mexico. (From
Velez-Juarbe et al., 2012)

The differences in morphology within each multispecies community suggest that ancient dugong species partitioned food resources. Resource competition may have led to differences in size and in traits related to feeding (tusk and skull shape). The smaller species in each assemblage likely foraged in very shallow waters (less than 1 meter deep) and perhaps on different sea grass species than the large-bodied dugongs in the community. Furthermore, the researchers suggest that the larger tusked dugongs in the community may have acted as keystone species by limiting the takeover of one sea grass species. The resulting sea grass communities were more diverse and offered opportunities for interspecific competition to drive evolution of several morphologically unique dugong species in each community.

Why multispecies sirenian communities disappeared leaving a single species in each region of the world remain a mystery, but changes in the diversity and abundance of sea grasses may have played a pivotal role.


References

Velez-Juarbe, J., Domning, D., & Pyenson, N. (2012). Iterative Evolution of Sympatric Seacow (Dugongidae, Sirenia) Assemblages during the Past ∼26 Million Years PLoS ONE, 7 (2) DOI: 10.1371/journal.pone.0031294
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Right Whales Stressed by Shipping Traffic

Tragic events often have unintended and far-reaching consequences. The destruction of the World Trade Towers by terrorists on September 11th 2001 was just such an event. It goes without saying that there were many consequences for humans, including two wars, increased airline screening, and shifts in the political landscape. But there were also consequences for other mammalian species as well.

Endangered North Atlantic right whales (
Eubalaena glacialis) gather during the late summer on calving grounds in the Bay of Fundy, Canada (Figure 1). A substantial portion of the calving grounds lies in an important shipping lane. Low frequency noise produced by ship engines and propellers travels long distances in water and is believed to interfere with acoustic signaling by whales. Previous studies have shown that right whales alter their vocalizations in response to increased underwater noise.

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Figure 1. A map of the Bay of Fundy, Canada showing the Right Whale Conservation Area and the shipping lanes. (From Rolland et al., 2012)

Rosalind Rolland from the New England Aquarium in Boston, and seven colleagues from across the United States, were collecting data on social behavior in right whales in the Bay of Fundy in August and September 2001. When shipping traffic ceased following the events of September 11
th, it presented the researchers with an unintended natural experiment. They realized that they had data that could test the hypothesis that shipping noise directly altered the behavior of North Atlantic right whales.

The researchers collected acoustic data, shipping traffic data, and fecal samples for right whales. The later were used to measure stress hormones (glucocorticoids) produced by the whales. Their results reveal a significant drop in low-frequency background noise in the days immediately following September 11
th when shipping traffic stopped in the Bay of Fundy (Figure 2).

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Figure 2. Power spectrum of underwater background noise from 2 days before and 2 days after 11 September 2001. There is a significant decline in low-frequency (< 150 Hz) noise after September 11 when shipping traffic stopped. (From Rolland et al., 2012)

Interestingly, the decline in background noise was correlated with decreased levels of stress hormones in right whales (Figure 3).

whale3
Figure 3. (a) Fecal glucocorticoid levels in North Atlantic right whales before (grey boxes) and after (white boxes) 11 September for the years 2001–2005. (b) Significantly lower Fecal GC levels were significantly lower after 11 September only in 2001, when shipping traffic stopped for a few days resulting in a decrease in underwater low-frequency noise. (From Rolland et al., 2012)

This fortuitous study represents the first direct link between shipping traffic noise and stress levels in whales. It suggests that whales congregating in high traffic shipping lanes are chronically stressed by noise pollution.


References

Rolland, R., Parks, S., Hunt, K., Castellote, M., Corkeron, P., Nowacek, D., Wasser, S., & Kraus, S. (2012). Evidence that ship noise increases stress in right whales Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2429



Tarsiers -- Communication in the Ultrasound

It is difficult for humans to imagine that a world of color and sound exists outside of the one that we can perceive, but for some organisms that world is a reality. Usually these animals aren't ones that we can readily relate to; bats and dolphins are two examples that both possess the ability to hear and emit high-frequency Read More...