Short Communication |
Corresponding author: Antonio Santos-Moreno ( asantosm90@hotmail.com ) Academic editor: Ana Maria Leal-Zanchet
© 2019 Antonio Santos-Moreno, Marina Soriano-Cruz.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Santos-Moreno A, Soriano-Cruz M (2019) Diet of Natalus mexicanus (Chiroptera, Natalidae) in a semi-evergreen forest in Oaxaca, Mexico. Neotropical Biology and Conservation 14(4): 591-598. https://doi.org/10.3897/neotropical.14.e46957
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We investigated the diet composition of Natalus mexicanus in a semi-evergreen forest in the state of Oaxaca, in the southeast of Mexico, using fecal analysis. The diet was composed of eight arthropod orders, the most abundant and important preys being members of the orders Diptera, Coleoptera, Hemiptera, and Hymenoptera. We did not observe significant differences in diet composition between males and females or in proportions consumed by the bats and those obtained through collections with light traps. In the study area, N. mexicanus is a species with a generalist opportunist diet.
Investigamos a composição da dieta de Natalus mexicanus em uma floresta perenifólia no estado de Oaxaca, no sudeste do México, utilizando análise fecal. A dieta foi composta por oito ordens de artrópodes, sendo as presas mais abundantes e importantes foram membros das ordens Diptera, Coleoptera, Hemiptera e Hymenoptera. Não observamos diferenças significativas na composição da dieta entre machos e fêmeas ou nas proporções consumidas pelos morcegos e aquelas obtidas através de coletas com armadilha luminosa. Na área de estudo, N. mexicanus é uma espécie com dieta oportunista generalista.
Diptera, diversity, Coleoptera, Hemiptera, Hymenoptera, Insecta
Diptera, Diversidade, Coleópteros, Hemípteros, Himenópteros, Insecta
The family Natalidae includes small bats from the tropics of the New World that consume insects of small size. The Mexican greater funnel-eared bat Natalus mexicanus Miller, 1902, the only species of the family Natalidae that occurs in Mexico (
Studies of bat diets have used analyses of stomach contents, feces, parts of prey remains, and direct observations (
Feces of N. mexicanus were collected in the surroundings of the cave El Apanguito (15°52'58"N, 96°21'13.2"W, 715 m.a.s.l.). It is located in the municipality of Santa Maria Huatulco, in the south-southeast of the state of Oaxaca, region of Costa, in the southeast of Mexico. The predominant vegetation is semi-evergreen forest mixed with coffee plantations. The climate is hot sub-humid with rainfall in the summer (monthly average of the season 216.5 mm) and the annual temperature is 28 °C. Six monthly samplings were carried out from August to October 2016 and from December to February 2017.
The diet composition of N. mexicanus was investigated using fecal analysis. For bat capture we placed a 7.5 m mobile harp trap at the entrance of the roost (
Each fecal sample was dried at room temperature and the number of pellets per individual was counted. Samples were weighed in an analytical balance, washed in 70% alcohol in a Petri dish, and separated with a dissecting needle, taking care not to damage the parts of arthropods in the sample. Each sample was observed and analyzed under a stereomicroscope. Each arthropod part that could be identified was compared with an entomological reference collection obtained at the same site during the sampling season.
Arthropod collection. A reference collection was obtained in order to identify the prey (
Data analysis. For each insect order recorded in the feces, we calculated the relative abundance (RA) and the importance index (II) modified by
and
where nik = mínimun number of remains of the order i in the sample j, nj = total number of remains in the sample j and U = total number of samples.
We compared the consumption of the different orders between males and females with a Mann-Whitney U test, and evaluated selectivity by comparing the differences between the proportions consumed by the bats and those from the collections using a Chi-squared test. To evaluate the diet diversity of N. mexicanus, we used Simpson’s reciprocal index (1/DS) because it is less sensitive to variations in sample size and gives less weight to rare taxa. This index uses values from 1 to the sample number of species, or in this case, the number of insect orders found in feces. Trophic breadth was analyzed with the Levins index, which takes values from 0 to 1: values higher than 0.6 indicate a generalist diet and lower values indicate a specialist diet (
A sampling effort of 540 meters∙trap/hour resulted in the collection and analysis of 23 fecal samples of N. mexicanus, 10 from females and 17 from males, where we observed a total of 163 insect remains, 143 of which could be identified to order level. Both sexes’ diet was composed of eight arthropod orders, whereas 15 orders were recorded in the collections. The most abundant and important prey were members of the orders Diptera (RA = 29.45, II = 38.62), Coleoptera (RA = 26.99, II = 27.22), Hemiptera (RA = 12.88, II = 13.1), and Hymenoptera (RA = 10.43, II = 10.8%). Members from the other four insect orders showed abundances of less than 10% and an importance of less than 5% (Table
Relative abundance (RA) and importance index (II) of insect orders consumed by Natalus mexicanus in a semi-evergreen forest in Oaxaca, Mexico. Both measures are expressed as percentages.
Order | RA | II |
---|---|---|
Diptera | 29.45 | 38.62 |
Coleoptera | 26.99 | 27.22 |
Hemiptera | 12.88 | 13.10 |
Hymenoptera | 10.43 | 10.80 |
Psocoptera | 2.45 | 3.65 |
Lepidoptera | 3.07 | 3.43 |
Ephemeroptera | 1.84 | 2.21 |
Dermaptera | 0.61 | 0.96 |
Natalus mexicanus exhibits a diet composed of members of eight orders: Coleoptera, Dermaptera, Diptera, Ephemeroptera, Hemiptera, Hymenoptera, Lepidoptera, and Psocoptera; where four of them were the most abundant and important. Even though there are only a few studies on the diet of N. mexicanus, it is known that this species feeds on small insects (
In the case of the order Coleoptera, it is likely that their high abundance in feces is, at least partially, the result of the hardness of their exoskeleton, which is more difficult to digest than the remains of members of other orders. For example, beetles were about 3.2 times harder than moths of the same body size (
We did not find differences in diet composition between males and females in the study area. However, even though it has been rarely evaluated in insectivorous bat species, such differences have been observed in the European free-tailed bat Tadarida teniotis (
In the case of diversity and breadth of the diet, we found that N. mexicanus exhibits moderate diversity and a generalist diet. Previous studies with insectivorous species suggest that species of small size, like N. mexicanus, fly at low speeds and, thus, encounter rates with many prey types are low and individuals are not expected to be very selective (
The results of the present study and its differences with other studies show that, in the area studied, Natalus mexicanus is an opportunistic predator, with a low diversity in its diet, and whose main prey are Diptera, Coleoptera, and Hymenoptera.
We are grateful to Dulce Itandehui Hernández Aguilar for her help with the field work and to Ricardo Balam Narvaez for providing valuable comments on previous versions of the manuscript. We also thank the Instituto Politécnico Nacional de México for providing financial support for the implementation of the project (grants SIP-20161645 and SIP-20171154 to the first author).