Trophic niche flexibility in Glossophaga soricina: how a nectar seeker sneaks an insect snack

Abstract

2W1 Summary 1.Omnivory enables animals to fill more than one trophic niche, providing access to a wider variety of food resources with potentially higher nutrient value, particularly when resources become scarce. Animals can achieve omnivory using different strategies, for example opportunistic foraging, or switching between multiple trophic niches. 2. The Neotropical bat Glossophaga soricina (Pallas, 1766) is a common and widespread species known for nectar feeding, but it also eats fruit and insects. Approaching stationary objects (flowers and fruits) or moving objects (insects) poses different sensory tasks and should require different echolocation behaviours. Here we tested the contrasting hypothesis that G. soricina can approach both stationary and moving objects using the same echolocation behaviour, thus feeding at different trophic levels by a single sensory mechanism. 3. Using DNA barcoding, we demonstrate that G. soricina eats beetles (Coleoptera), flies (Diptera) and noctuid moths with bat-detecting ears. Laboratory observations show that G. soricina actively hunts for prey so insect consumption does not appear to be opportunistic. After capture, individuals consumed prey while perched and manipulated them with jaw, thumb, wrist and wing movements, but food handling was longer and chewing rate slower than in obligate insectivores. 4. In contrast to most insectivorous bats, the echolocation calls of G. soricina are of high frequency and low intensity, and G. soricina did not produce feeding buzzes when approaching insects. An acoustic model of detection distances shows that its low-intensity calls fail to trigger the auditory neurons of eared moths, allowing G. soricina to overcome auditory prey defences. 5. Individuals achieved niche flexibility using a unique but generalist behavioural approach rather than employing two different specialist methods. Our findings provide a novel insight into the functional mechanisms of insect capture in G. soricina and highlight the importance of considering niche flexibility in classifying trophic links in ecological communities.

The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

“…Even within the food web targeted, some taxa involved are simply too secretive to ever be seen eating each other (cf. Clare et al 2014aClare et al , 2014bClare et al , 2014cWirta et al 2014), or too fragile or otherwise difficult to handle (such as gelatinous zooplankton in aquatic webs: Arai 2005; Majaneva 2014 and references therein) to be comprehensively examined. Thus, we tend to end up with describing a subset of interactions cut out of their larger context.…”

A New Family of Large Omnivorous Bats (Mammalia, Chiroptera) from the Late Eocene of the Fayum Depression, Egypt, with Comments on Use of the Name “Eochiroptera”

“…Carnivorous bats often eat insects; insectivorous bats may occasionally eat small vertebrates, fruit, or nectar; frugivorous bats may supplement their diets with insects; and nectarivorous bats may also eat insects and fruit (Howell, 1974;Gardner, 1977;Freeman, 2000;Mello et al, 2004;Frick et al, 2009;Rex et al, 2010;Dumont et al, 2011;Santana et al, 2011b;Clare et al, 2014;Novaes et al, 2015;Yohe et al, 2015). Diets of some (perhaps many) bat species may also shift dramatically with season (Howell, 1974;Sosa and Soriano, 1996;Mello et al, 2004;Richards et al, 2008;Rex et al, 2010;Clare et al, 2014). However, most bat species appear to have morphological specializations for fruit, nectar, or animal-based diets (Freeman, 1984(Freeman, , 2000Dumont, 2003;Swartz et al, 2003, Winter andVon Helverson, 2003) and rely entirely or primarily on one type of food at least in some seasons of the year (Gardner, 1977;Freeman, 1984Freeman, , 2000, thus allowing the categorizations described above.…”

“…However, most bat species appear to have morphological specializations for fruit, nectar, or animal-based diets (Freeman, 1984(Freeman, , 2000Dumont, 2003;Swartz et al, 2003, Winter andVon Helverson, 2003) and rely entirely or primarily on one type of food at least in some seasons of the year (Gardner, 1977;Freeman, 1984Freeman, , 2000, thus allowing the categorizations described above. Clear exceptions exist, however-true omnivorous bats that routinely consume a variety of food types including both animal and plant products (Gardner, 1977;Arkins et al, 1999;Lloyd, 2001;Rex et al, 2010;Dumont et al, 2011;Clare et al, 2014;Yohe et al, 2015). These taxa all belong to the Neotropical family Phyllostomidae and the related New Zealand/Australian endemic family Mystacindae.…”

“…One particularly flexible species is Glossophaga soricina (7-12 g), a small phyllostomid that lives in habitats ranging from columnar cactus deserts to wet tropical rainforests, and which has been variously described as an obligate nectarivore (e.g., Heithaus et al, 1975), seasonal insectivore (e.g., Howell, 1974;Howell and Burch, 1974), mostly frugivorous (e.g., Willig, 1986), and as an omnivore (e.g., Henry and Stoner, 2011), depending on when and where the population was studied (Clare et al, 2014). Review of dietary studies and foraging behavior of Glossophaga soricina strongly suggests that it can flexibly switch between trophic niches (plant versus insect foods) and may do so regularly, hence it is best classified as a highly flexible omnivore (Clare et al, 2014).…”

“…Review of dietary studies and foraging behavior of Glossophaga soricina strongly suggests that it can flexibly switch between trophic niches (plant versus insect foods) and may do so regularly, hence it is best classified as a highly flexible omnivore (Clare et al, 2014). In terms of its dentition, Glossophaga is one of the less-derived "nectarivorous" bats studied by Freeman (1995)-it retains dilambdodont molars that are of moderate size, are only slightly buccolingually compressed, have a relatively large stylar shelf, and M3 is retained as a large tooth with a N-shaped ectoloph (Freeman, 1995;Dávalos et al, 2014: P891).…”