| Summary: | 碩士 === 國立成功大學 === 生命科學系 === 102 === Ecological morphology presents constraints and opportunities to how animals explore resources by different mechanisms, and in turn may affect the resource use patterns of animals. Closely-related species with similar eco-morphological traits are presumably subjected to similar limitations, and thus are expected to explore similar resources. On the other hand, closely-related species may still display substantially different resource use, because slight differences in key eco-morphological traits may influence their performance and efficiency in exploring environments and resources.
For microchiropterans, wing-shape parameters and echolocation structure often limit the type of habitats they are capable of exploring, which will affect the type of prey encountered. Body size, skull size, and tooth structure may further constrain size or hardness of prey consumed by bats. This study tested the hypothesis that small differences in crucial eco-morphological traits between congeneric species may contribute to different food habits. I conducted dietary analyses on fecal samples of two closely-related insectivorous bats, Hipposideros terasensis Kishida, 1924 and H. turpis Bangs, 1901, which were collected in their summer habitats. These two species differ in body size, skull size, and echolocation call frequency. I also measured related wing parameters, including span, area, and loading of wing, aspect ratio, tip length and area ratios of wing, and wingtip shape index, for these two species to compare their wing morphology.
The diet of H. terasensis comprised of 9 insect orders, and that of H. turpis additionally included Araneae, Odonata, and Trichoptera and contained a total of 12 orders of arthropods. Both species fed primarily on Coleoptera that accounted for more than 20% in frequency of occurrence and about 40% in volume percentage, while the rest prey orders accounted for different proportions in their respective diets. Hemiptera and Hymenoptera accounted for 53.8% of the total frequency of occurrence and contributed to 50.8% of the volume in the diets of H. terasensis. In contrast, Orthoptera, Hemiptera, and Blattodea were more prevalent in the diet of H. turpis, but Orthoptera and Lepidoptera were more abundant in volumes. Below the level of order, I found 21 and 13 prey taxon, mostly families, in the diets of H. terasensis and H. turpis, respectively. Within hemipterans, H. terasensis consumed higher proportions of cicadas than H. turpis. Overall, H. terasensis displayed a more even and thus a more heterogeneous diet than that of H. turpis, with a medium dietary overlap between the two species at 0.67, based on Horn’s index of similarity.
Most wing parameters measured were higher in H. terasensis than those of H. turpis. A higher wing loading and aspect ratio indicate a faster but less maneuverable flight for H. terasensis. In contrast, the flight of H. turpis is expected to be more maneuverable and adapted to near vegetation and the ground. In addition, H. turpis with higher call frequency would be more tolerant to cluttered environments. Incorporating the general flight potentials of insects, dietary results showed that H. terasensis, with higher wing loading and aspect ratio, consumed a higher proportion of faster-flying insects, such as Hymenoptera. The larger body and skull size of H. terasensis suggest a more powerful bite force, and the estimated hardness index of prey eaten by H. terasensis (3.75) was slightly higher than that of H. turpis (3.67).
The food habits differed between H. terasensis and H. turpis in several aspects, and various factors might have contributed to these differences. The dietary results were consistent with the predictions from eco-morphological traits, including body size, wing parameters, and echolocation. Since H. terasensis ate more evenly among each insect order, it ate less number of insect orders but had a more heterogeneity diet. This study did not measure food availability on site, thus can’t rule out the possibility of dietary differences affected by prey availability. The dietary compositions of H. terasensis among sites across Taiwan, however, indicate little dietary variation in space and substantiate our conclusions. Eco-morphological traits constrain animals to explore resources and to a certain extent that have contributed to the different patterns of resource use, thus eco-morphological traits can be a good indicator for resource use patterns of animals with caution.
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