James S. Findley

The Structure of Bat Communities

Multivariate morphometric analysis of faunas may provide a useful estimate of ecologic structure. Tropical bat faunas resemble one another in faunal statistics despite trenchant taxonomic differences, suggesting common evolutionary pressures in three tropical regions. Each fauna consists of many similar closely packed, overlapping, relatively invariable species and a few distinctive, distant, isolated, variable kinds. Temperate and tropical faunas differ in the greater rarity, or even absence, of highly distinctive taxa in the former but are not meaningfully different in packing or degree of overlap.

Morphologic Properties of Bat Wings

A method was devised for estimating aspect ratio, wing ratio, wing area, wing loading, and wing length from study skins of bats. These measures were taken of 136 species representing 15 families. Wing area and loading are positively, and wing length negatively, correlated with size. Aspect and tip ratios are independent of size and of each other. Distinctive combinations of some of these variables characterize groups of bats that presumably have similar flight modes. Speed is positively correlated with aspect ratio and tip index, but regresses significantly only on the former. Long tips coupled with low aspect ratio may characterize hoverers. Long wings and short tips may characterize bats that are capable of remaining airborne at slow speeds. Most bats with low aspect ratios are forest dwellers, whereas species with high aspect ratios are migrants and foragers in open areas.

Seasonal Distribution of the Hoary Bat

Distributional records of hoary bats, Lasiurus cinereus Peale and Beauvois, were assembled and mapped for each month. In North America females are seen to migrate northward somewhat earlier than males and to occupy an eastern summering ground where young are born, while males are concentrated in western North America. Fall migration begins in August. Spring and fall migratory waves have been noted, some segregated as to sex. Some South American hoary bats migrate, while others may be non-migratory.

Observations on the neotropical disk-winged bat, Thyroptera tricolor spix.

Study of 42 marked Thyroptera tricolor in Puntarenas Province, Costa Rica, revealed that the animals live in groups of six to seven individuals. The members of each group always roost together in a rolled leaf of a plant, usually of the genus Heliconia. Each roost is occupied for one day. Each group seems to occupy an exclusive roosting area that averages 3000 square meters. The disk-winged bat, Thyroptera tricolor Spix, is one of two species in the Neotropical family Thyropteridae. It occurs from southern Mexico through much of tropical South America. A second species, T. discifera, occurs in parts of Central and South America. These small, delicately built bats (average weight about 4 grams) have forwardly directed funnel-shaped ears and very small eyes like funnel-eared bats (family Natalidae) and smoky bats (family Furipteridae). Thyroptera differs from bats of these other two Neotropical families, however, in having well-developed suction disks located at the wrist and on the ventral surface of the hind foot. These disks, the anatomy and functioning of which have been studied in detail by Wimsatt and Villa (1970), allow the animal to attach itself to smooth surfaces, such as leaves or glass. So far disk-winged bats are known to roost only inside the rolled new leaves of members of the banana family (Musaceae) or related plants. Within the leaves the bats arrange themselves in a vertical row in a head-up posture, attaching themselves to the leaves by means of the suction disks. Our studies of these bats in lowland Costa Rica revealed that the number of suitable roosts in a given area on any given day is very limited. Thus it is possible to locate all the potential roosts and find the resident bats with a considerable degree of predictability. After capture the animals may be marked for future recognition, and relocated at will. Here we present the results of two weeks of study of these intriguing little bats in Puntarenas Province, Costa Rica. Our findings suggest that the bats are organized into roosting colonies, that the members of each colony remain together, rejoining even if separated, and that each colony occupies an exclusive roosting area.

Ecological Significance of Chiropteran Morphology

That form is related to function in animal life is a concept that goes back at least to Aristotle. Relating structure to function has been a central occupation of anatomists, and the subject of functional morphology has a dedicated following. Yet the suggestion that an organism’s ecological role can be predicted from its morphology often elicits opposition. Because behavior is so flexible, individual animals may do many things that a study of their anatomy would not predict. Ducks with bills highly specialized for filtering small particles from water and mud may, nevertheless consume small vertebrates, centipedes, lettuce, corn, and dog food with great skill. The objection to making ecological predictions from morphology seems to be that although we can assert that a bat eats fruit because its teeth are constructed in a certain way, because of the observed variability in dietary proclivities of individual fruit bats we cannot make more refined predictions about the size and kind of fruit consumed, the extent to which animals are eaten, the nature of seasonal changes in diet, and so on. Our contention is that because the selective regimen imposed on a species through evolutionary time includes these minor variations, they are probably reflected in a bat’s phenotype. By comparing the morphology of members of a feeding guild of bats, it should be possible to predict ways in which the several species differ in food habits, foraging styles, shelter seeking, and other ecological traits.

Sexual Size Dimorphism in Vespertilionid Bats

Sexual size dimorphism was investigated in 18 species of vespertilionid bats (Chiroptera: Vespertilionidae). The characters representing size were length of head and body (HBL), length of forearm (FAL), condylocanine length (CCL) and length of maxillary toothrow ( MTL ). From these variables, two proportional characters were calculated, HBL/FAL and CCL/MTL. Students t-tests were used to determine significant differences (P ^ 0.05). Females averaged larger than males in two or more size dimensions for all 18 species, with significant differences being noted in 15 of the species. In no cases were males significantly larger than females. Proportional differences were fewer, with significant differences being found in only five species. Mean lengths of forearm and maxillary toothrow were adjusted by covariance analysis in order to negate the differences in absolute size between the sexes. Using this procedure, females of six species had significantly longer forearms than males, and males of one species had significantly longer forearms than females. There were no significant correlations between the number of young per pregnancy and the degree of dimorphism exhibited by the species tested. The general patterns in these data, when coupled with life history information, suggest that increased energy demands during pregnancy may be the primary factor in the selection for larger size in females. Larger females can maintain homeothermy, and hence the timing of birth, more efficiently, can store more fat, and have a greater size array of prey available to them. Increased weight loading of pregnant females is probably also important in the selection of larger size in females, but this hypothesis is not supported by these data.

A SEARCH FOR PATTERN IN BUTTERFLY FISH COMMUNITIES

The species richness and individual abundance of butterfly fishes increase with coral density. There is no evidence of either density compensation or place-niche compression as the number of species increases from 2 to 17, although place-niche overlap does increase slightly along this gradient. Real place niches and overlaps are uniformly less than ones calculated for randomly generated communities of noninteracting species. Pairwise comparisons of species based on abundance at 14 stations revealed more positive correlations than expected, suggesting that all fishes are more common at favorable stations. Species are not randomly distributed among transects within stations, and the lower-than-expected place-niche overlap between them suggests differential habitat selection on this scale. A comparison of matrices of morphological resemblance, coexistence, and diet revealed no correlations of the sort expected if similar species were replacing each other from site to site. Our results provide little evidence that butterfly fishes are living in resource-limited communities, and suggest that their assemblages are not competitively structured. However, the communities are not random assemblages of the species of which they are composed.

GLOBAL, REGIONAL, AND LOCAL PATTERNS IN SPECIES RICHNESS AND ABUNDANCE OF BUTTERFLYFISHES

Butterflyfish communities vary in richness longitudinally from highs of >30 species to lows of 2–3 species. We investigated this gradient because it provides an opportunity to address some basic questions relating to determinants of community structure, e.g., are richness and abundance functions of geography or of local conditions? How are richness and density of species populations related? Do community-level processes, such as competition, determine community structure? In a broader sense, to what extent are community properties internally deterministic as opposed to being functions of higher-level processes? From 1981 through 1997 we counted kinds and number of butterflyfishes on over 2000 10-min transects distributed from the eastern Caribbean to the western Indian Ocean and Red Sea. We grouped transects at the same site into stations, stations in the same local area into islands, and islands into 18 geographic regions, thus organizing the data into four spatial levels. For each station, extent of live coral cover and degree of open-ocean influence were estimated. Richness is highest in the Philippine–Bornean–New Guinean region and declines radially from that center. Total number of individual butterflyfish also declines over that gradient. On more local scales, increased open-ocean exposure and live-coral cover enhance both richness and numerical abundance. Because species richness declines more rapidly with distance from the richness center than does abundance, across the same gradient average abundance per benthivore species rises. In peripheral, species-poor reaches of the Indopacific, the Eastern Tropical Pacific, and the Caribbean the communities are dominated by one or a few very common species. Butterflyfishes respond to changing richness of their communities by adjusting the abundance of individual species. Use of space by individual species decreases with increasing richness. Global richness is determined chiefly by geography; within local areas local factors are more important. Community structure is predominantly organized by richness, hence first by geography and then by habitat characteristics.

Geographic Variation in Pipistrellus Hesperus

Geographic variation in Pipistrellus hesperus consists of an eastern series of populations of large individuals and a western series of populations of small individuals, this situation perhaps resulting from historical changes in the distribution of deserts. Other facets of geographic variation involving color, sexual dimorphism, and variability are discussed in relation to climate, rainfall, and sexual differences in behavior.

Taxonomic Relationships of Bats of The Species Myotis Fortidens, M. Lucifugus, and M. Occultus

Myotis lucifugus and M. occultus are considered to be conspecific, the older name, M. lucifugus , applying to both. Myotis fortidens is a tropical Mexican species differing from M. lucifugus in a number of ways. In both species skull size seems to be related to number of species of Myotis living in the area from which a given sample originated. Body size seems related to climatic severity.