BULLETIN of the FLORIDA STATE MUSEUM Biological Sciences
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BULLETIN of the FLORIDA STATE MUSEUM Biological Sciences Volume 24 1979 Number 4 FORAGING AND REPRODUCTIVE ECOLOGY IN A PANAMANIAN BAT COMMUNITY FRANK J. BONACCORSO S . UNIVERSITY OF FLORIDA GAINESVILLE Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. JOHN WILLIAM HARDY , Editor RHODA J . RYBAK , Managing Editor Consultants for this issue.· RAYMOND HEITHAUS THOMAS H. KUNZ Communications concerning purchase or exchange of the publications and all manuscripts should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of Florida; Gainesville, Florida 32611. Copyright © 1979 by the Florida State Museum of the University of Florida. This public document was promulgated at an annual. cost of $1,679.36, or $1.679 per copy. It makes available to libraries, scholars, and all interested persons the results of researches in the natural sciences, emphasizing the circum-Caribbean region. Publication date: December 20,1979 Price: $1.70 FORAGING AND REPRODUCTIVE ECOLOGY IN A PANAMANIAN BAT COMMUNITY FRANK J. BONACCORSOl SYNOPSIS: Resource partitioning, reproduction, and community structure in a tropical moist forest community of 35 bat species were studied on Barro Colorado Island, Panama Canal Zone. Over a three-year span 2884 bats were captured, banded, and released; data were collected on food habits, activity cycles, habitat selection, and reproductive timing. Information on seasonality and abundance of fruit, flower, and in- sect resources used by bats also was collected. Fluctuating levels of food resources require that many bat species utilize different habitats and foraging strategies through a year. Competitive interactions, predator avoidance, and climatic fluctuations further influence foraging strategies. The bat com- munity is divided into nine feeding guilds on the basis of diet and method of food pro- curement. Within the most complex guilds food resources are partitioned temporarily, spacially, and by size and quality. Within the simplest guilds food resources are parti- tioned primarily by particle size. Reproduction coincides with high levels of food availability. Species utilizing food sources abundant over most of the year have two litters per year. TABLE OF CONTENTS INTRODUCTION. .. 360 ACKNOWLEDGEMENTS . 361 STUDY AREA 361 MATERIALS AND METHODS 361 PHENOLOGY OF FOOD RESOURCES, . 363 RESOURCE PARTITIONING . 365 CANOPY FRUGIVORE GUILD . .. 368 GROUNDSTORY FRUGIVORE GUILD .. 377 SCAVENGING (OR JuICER) FRUGIVORE GUILD . 380 NECTAR-POLLEN-FRUIT-INSECT OMNIVORE GUILD 381 SANGUIVORE GUILD . 383 GLEANING CARNIVORE GulLD 385 SLOW-FLYING HAWKING INSECTIVORE GUILD 388 REPRODUCTION 390 CANOPY FRUGIVORE GUILD . 391 GROUNDSTORY FRUGIVORE GuILD . 393 SCAVENGING FRUGIVORE GUILD .. 394 NECTAR-POLLEN-FRUIT-INSECT OMNIVORE Gu ILD 394 SANGUIVORE GUILD .... 394 GLEANING CARNIVORE GUILD . 395 SLOW-FLYING HAWKING INSECTIVORE GUILD . 396 DISCUSSION . 397 DIVERSITY AND PHENOLOGY, .. ,. 397 FORAGING AND REPRODUCTIVE STRATEGIES 399 LITERATURE CITED . 406 'The author is Adjunct Assistant Professor, Biology Department, University of Wisconsin-Eau Claire, Eau Claire, Winconsin 54701. This study was submitted as partial fulfillment of the Ph.D. degree in the Department of Zoology, University of Florida, Gainesville, 32611. BONACCORSO, FRANK J. 1978. Foraging and Reproductive Ecology in a Panamanian Bat Community. Bull. Florida State Mus., Biol. Sci. Vol. 24(4):359-408. 360 BULLETIN FLORIDA STATE MUSEUM Vol. 24, No.· 4 INTRODUCTION The words "tropical forest" typically engender visions of species- rich communities, complex competitive interactions, and relatively stable environments. Indeed, faunal lists in the tropics are large, and food webs are intricately complex. It is also true that organisms in- habiting tropical lowlands usually are subjected to less extreme en- vironmental fluctuations than are their counterparts in temperate or polar regions. However, it is too infrequently emphasized that even species in tropical forests must possess behavioral flexibility to counter and survive climatic and biotic environmental change. There are two major reasons for this oversight. First, few detailed studies of I tropical organisms have spanned periods of several years or even seasons, and second, behavioral responses of tropical species to en- vironmental fluctuations are often quite subtle. Whereas temperate animals commonly exhibit obvious and dramatic responses to seasonal change such as hibernation or long distance migration, tropical species may need only to switch food types or microhabitats, or briefly halt reproduction (Kaufmann 1962, Wolf 1970, Mares and Wilson 197la, Snow and Snow 1972, Orians 1973, Montgomery and Sunquist 1973). Nevertheless, genetic and behavioral flexibility are requisites of sur- vival for most tropical as well as temperate species. Tropical bats are particularly good subjects for studies of diversi- ty, competitive interaction, and response to environmental fluctuation because of their individual abundance and the complex taxonomic and ecological communities they form. About 100 species of bats occur in each of the small countries of Central America (Hall and Kelson 1959). It is common to find 30 to 50 species in one macrohabitat measuring a few square kilometers in area. Among tropical bat species, few are known or suspected to reproduce year round or to specialize on constantly abundant food resources; the common vampire bat, Desmodus rotundus, being a notable exception on both counts (Wimsatt and Trapido 1952, Turner 1975). Most bats in equatorial regions are seasonally polyestrous or monestrous in reproduction (Baker and Baker 1936, Mutere 1970, Fleming 1973) and make seasonal shifts in diet (Wilson 197lb, Flem- ing et aL 1972, Heithaus et al. 1974). The objective of this paper is to delineate adaptive strategies used by tropical bats that enable them to survive and reproduce under fluc- tuating environmental conditions and coexist with numerous similar species in complex communities. The field work represented herein documents seasonal changes in food resources, mechanisms of resource partitioning, and reproductive timing through one complete year and portions of two other years. 1979 BONACCORSO: A PANAMANIAN BAT COMMUNITY 361 ACKNOWLEDGEMENTS This study was funded by NSF Grant GB-36068 to J. H. Kaufman, NIH Biomedical Sciences Grant No. RR7021-07 from the Division of Sponsored Research, University of Florida, to S. R. Humphrey, and the Environmental Sciences Program, Smithsonian Tropical Research Institute. The Florida State Museum and Smithsonian Tropical Research Institute provided logistical support. B. K. McNab, both in his writings and classroom dhcussions, induced and encour- aged the germ plasm of interest that launched me intu the study of the ecology of tropical bat communities. S. R. Humphrey provided heig and encouragement through all phases of the study, including assistance with field work in January 1973. J. H. Kaufmann, E. Leigh, A. S. Rand, N. Smythe, A. F. Carr, D. H. Hirth, and T. C. Emmel took time to provide constructive guidance. Robin Foster verified my seed identifica- tions and cultured in me a deep appreciation for tropical plant ecology. Clark Sandford, Julie Wiatt, Bill Biven, and Janet Hall faithfully assisted with fieldwork and laboratory preparations under trying conditions. Nancy Halliday and Sylvia Scudder used their creative talents to render the illustrations. Insects eaten by bats were identified by Terry Zinn. Finally, I wish to thank the scientists, students, and visitors coinciding with my residence on BCI, as well as the Smithsonian staff, for providing encourage- ment, friendship, intellectual atmosphere, and volleyball at an isolated field station. STUDY AREA The primary research site was Barro Colorado Island (BCI), which lies within freshwater Lake Gatun, Panama Canal Zone, at 9° 10' N Lat, 79° 51' W Long. This site was selected because it has a rich bat fauna, relatively undisturbed mature moist forest, modern living and laboratory facilities, and reference collections of animals and plants. A second site was located on the mainland opposite BCI at the base of Buena Vista Peninsula (Fig. 1). The climate of this lowland area of Panama is warm and humid, with a 7-month (May through November) wet season and a 3-month (January through March) dry season. Dry season months each receive less than 60 mm of rain, whereas wet season months typically receive in excess of 250 mm of rain. April and December are transition months between the dry and wet seasons and receive amounts of rain that vary considerably from year to year. Thus in years when April and December are very dry, the dry season may last for five months. Average annual rainfall since 1926 has been 2820 mm (Smythe 1974). Monthly sums of rainfall for 1973 are shown in Figure 3. During night-time sampling of bats, relative humidity under the forest canopy never fell below 80 percent. Measurements were made at 2 m above ground with sling pyschrometer. Daily temperatures on the forest floor fluctate from a mean minimum of 22.1°C to a mean maximum of 28.0'C, with no significant seasonal variation (Smythe 1974). Barro Colorado is in the Tropical Moist Forest life zone (Holdridge 1967). This 15 km' island is covered with forest that is over 60 years in age. The only physical disturb- ance results from recutting forest trails, maintaining a small