Tracking dietary habits of cave arthropods associated with deposits of hematophagous bat guano: A study from a neotropical savanna

Abstract

Carbon and nitrogen stable isotopes were used to track major dietary variations in arthropods found in a cave located in a neotropical savanna in Central Brazil. We determined the δ 13 C and δ 15 N for cave crickets, cockroaches, spiders, guano of a hematophagous bat, and leaf litter found on the ground near the cave entrance. The δ 13 C and δ 15 N for the cricket and cockroaches showed that bat guano was not the only food item for these arthropods. They had intermediate δ 13 C and δ 15 N between bat guano and leaf litter, which means that they consumed additional food resources other than guano in their diet, independent of distribution of guano deposits in the cave.The spiders, predators with great mobility, seemed to not have a preferential diet item since their isotope signals indicated they hunt both crickets and cockroaches. The δ 13 C of the bat guano (−15.4‰) indicated that the diet of these hematophagous bats relied on animals fed with C4 plants. The conversion of native savanna vegetation of which the debris is mostly from C3 plants, to pasture, based on C4 African grass, a remarkably common land use transformation in the region, is indirectly influencing the diet of hematophagous bats, which basically relied on exotic fauna. The C and N stable isotope ratios showed that the arthropods inside the cave do not rely solely on bat guano for their diet, but interact directly with the external environment, through litter debris, indicating a significant exchange of energy and matter between the cave environment and the surrounding area.

Bat aggregation mediates the functional structure of ant assemblages

“…Note that the trophic chain in the cave is likely based on what we called ''fresh'' guano (d 15 N = 3.52%) because ''older'' guano has higher d 15 N values than those found in fungus-growing ants (d 15 N = 9.29% vs. 6.03% and 7.19%; Table 1). These differences in bat guano d 15 N values can be compared to the diverse values noted between caves sheltering bats with different feeding habits: 5.2%-20.9% for the insectivorous bat, P. parnelli (the most frequent in the cave studied); 3.8%-7.0% for the frugivorous bat, Artibeus jamaicensis [65]; 23% on average for the hematophagous, vampire bat, Desmodus rotundus [15]. These results are consistent with those obtained from hollow, Neotropical trees that serve as bat roosts whose seeds were enriched in 15 N compared to control trees without bats, this is particularly true when the trees serve as roosts for vampire bats [66].…”

“…Guano-derived nitrogen had bottom-up effects on arthropod communities in that it primarily fostered non-predatory insects, while an analysis of d 15 N levels in predator tissues revealed the flow of nutrients to the top of the food chain. The ant model, with 15 N enrichment regardless of their functional group, suggests that the phenomenon extends to higher trophic levels involving birds and small mammals.…”

“…For instance, a large colony of Brazilian free-tailed bats redistributes 22 kg of nitrogen per year in the form of guano [9]. Also, bat guano provides the primary organic input in caves, supporting a great diversity of organisms belonging to different trophic levels [10][11][12][13][14][15].…”

Background and the use of isoscapes in the Brazilian context: essential tool for isotope data interpretation and natural resource management

“…The combination of δ 15 N and δ 13 C has been the basis for studies about diet of different animals such as aquatic macrofaunal (Hardt et al, 2013;Castro et al, 2016), fishes and dolphins (Di Beneditto et al, 2013), arthropods (Salgado et al, 2014) and small mammals (Galetti et al, 2016), and human diet in different regions of Brazil (Nardoto et al, 2006(Nardoto et al, , 2011Gragnani et al, 2014;Rodrigues et al, 2016).…”

Guano exposed: Impact of aerobic conditions on bat fecal microbiota

“…Chiroptera is a large and widespread mammalian order with more than 1,300 species of bats distributed worldwide, absent only in the Arctic, Antarctic, and some island chains. Bats provide important ecosystem services as pollinators, seed dispersers, and pest control agents (Kunz, de Torrez, Bauer, Lobova, & Fleming, 2011), and they serve as the foundation species in subterranean habitats (caves and abandoned mines) where their regular deposition of nutrient-rich guano supports a diverse food web (Emerson & Roarki, 2007;Ferreira & Martins, 1998;Salgado, Motta, De Souza Aguiar, & Nardoto, 2014). Bats are also increasingly recognized as an important reservoir for a number of human-and livestock-affecting viral (Krebs, Mandel, Swerdlow, & Rupprecht, 2004), bacterial (Brouqui & Raoult, 2006;Mogollon-Pasapera, Otvos, Giordano, & Cassone, 2009;Veikkolainen, Vesterinen, Lilley, & Pulliainen, 2014), and fungal pathogens (Daszak, 2000;Wood et al, 2012).…”