The bat population of the island of Curaçao, Netherlands Antilles, was surveyed in 1992 and 1993. The 1993 survey concentrated mostly on caves, which were found to host most of the bats. Glossophaga longirostris elongata was the most abundant species with fewer than 2000 individuals encountered. However, this species may also be found in small groups in buildings and caves that were not censused. More critical is the status of the other six species found on the island: Leptonycteris curasoae (800–1000), Mormoops megalophylla intermedia (570–650), Natalus tumidirostris (50–60), and three species for which the number of individuals is unknown and probably low: Myotis nesopolus, Pteronotus davyi and Noctilio leporinus. Three caves contain all of the above species, except N. leporinus, and should be actively protected. Two species expected to be present on Curaçao, Artibeus jamaicensis and Molossus pygmaeus, were not found. The apparent decrease in bat numbers this century is likely a result of uncontrolled cave disturbance and removal of resources through development. I propose that all species be considered endangered on the island of Curaçao, except for Glossophaga longirostris, which is threatened.
We estimated the population sizes of the three species of columnar cacti that grow on the island of Curaçao using ground and aerial transects, and we examined the island’s carrying capacity for two species of nectar-feeding bats that depend on nectar from the flowers of these cacti. We calculated carrying capacity based on the daily availability of mature flowers between January and December 1993 and the field energy requirements of bats as estimated from an equation for eutherian mammals (low estimate) and one for passerine birds (high estimate) based on body mass. Additional energy requirements of pregnancy and lactation were taken into account. We estimated that 461,172 columnar cacti were present on Curaçao (38% Subpilocereus repandus, 51% Stenocereus griseus, and 11% Pilosocereus lanuginosus). May through September are the critical months when bats rely most heavily on cactus for food. July 1993 was a bottleneck with the smallest number of mature flowers per day. July and August were months of greatest energy demand because females were lactating. We estimate that the carrying capacity for Glossophaga longirostris in July, when the bat (Leptonycteris curasoae) population was 900, was near 1200, an estimate that fits the observed population size of nectar-feeding bats on the island. We suggest that the extensive removal of native vegetation occurring on Curaçao be strictly regulated because further destruction of the cacti will result in a decrease and potential loss of the already low populations of nectar-feeding bats.
Three species of columnar cacti (Stenocereus gri seus, Subpilocereus repandus, and Pilosocereus lan uginosus) are conspicuous elements of arid vegetation in northern Venezuela and several nearby islands induding Aruba, Bonaire, and Curacao. Stenocereus griseus and Subpilocereus repandus produce most of their flowers and fruits during the dry season (from January to September) on Curacao, Netherlands Antilles (Petit 1995). They provide food for several species of animals (especially bats and birds) during part of the dry season, when many other plant species are non-productive. The major pollinators of these self-incompatible cacti in Venezuela are the bats Leptonycteris curasoae and Glossophaga longirostris (Phyllostomidae) (Nassar 1991). An exhaustive census showed that bats of all species, induding L. curasoae and G. longirostris were threatened on Curagao (Petit 1995). Unidentified sphinx moths and two species of hummingbirds are other potential cactus pollinators on the island. In the Sonoran desert, all three groups are important pol linators of columnar cacti (T. Fleming, pers. comm.), and in most systems studied so far, bats are not exdusive pollinators of key plants. I determined the importance of moths, birds, and bats as pollinators of S. griseus and S. repandus pollination on Curacao because bats were expected to contribute significantly to cactus pollination, and evidence of their ecological importance was needed to prompt conservation action for bats and caves.
Two sympatric species of columnar cacti on Curaçao, Netherlands Antilles, share bat pollinators, overlap in flowering phenology, and are floral homologues. Leptonycteris curasoae curasoae and Glossophaga longirostris elongata (Chiroptera: Glossophaginae) visit flowers of Stenocereus (syn. Ritterocereus) griseus and Subpilocereus (syn. Cereus) repandus on the same nights; these visits may promote interference competition between cactus species. I studied the effect of heterospecific (mixed) pollen loads on fruit and seed set, fruit and seed size and mass, germinated seeds at 5 weeks, and seedling survival at 7 months in relation to hand pollination with intraspecific pollen and natural pollination. Hand pollination seemed to limit pollen loads available for pollination. Under these conditions, natural pollination tended to produce the most fruits and seeds, and the largest fruits (but lightest seeds); mixed pollination was the least effective treatment (fruit set was significantly greater for St. griseus in natural than mixed pollination; fruit volume was greater in natural than mixed pollination for S. repandus, and seed number and fruit mass were larger in intraspecific than in mixed pollination). Aspects of natural pollination, possibly repeated visits, compensated for the negative impact of interspecific pollen loads under pollen limitation, with positive impacts on the carrying capacity of cacti for frugivores. Seed mass from natural pollination was negatively correlated with seed number only for St. griseus. Germination success was not correlated with seed mass, but seedling survival at 7 months was for S. repandus. The two species do not seem to compete through pollen interference when pollinator visits are relatively frequent.
We examined the potential for exploitation competition by differential attractiveness in two sympatric species of columnar cacti on Curaçao, Netherlands Antilles. Stenocereus griseus and Subpiloccreus repandus have temporally overlapping flowering phenologies and share pollinators. We examined nectar volume, energy contents, and sugar ratios for the entire night and at two-hour intervals in both cactus species. Except for a burst in nectar volume and sugar concentration by Subpilocereus repandus during the first two hours of anthesis, nectar secretion patterns, energy contents, and sugar ratios (70% hexose) were similar for the two species. The standing crops of nectar in both species were kept very low by bat pollinators. We suggest that the potential for exploitation competition between Stenocereus griscus and Subpilocereus repandus is currently very low on Curapo.
The phenological response by three sympatric species of columnar cacti of the semi-arid island of Curaçao (Stenocereus griseus, Subpilocereus repandus, and Pilosocereus lanuginosus) to recent rainfall was investigated during 21 months. Rainfall is the climatic cue most likely to affect bud formation on Curaçao, and each species of cactus responded differently to it. Pilosocereus lanuginosus started budding immediately after rainfall, whereas Stenocereus griseus responded negatively with abortions and cessation of bud production within 2–3 weeks after rain. Subpilocereus repandus showed no response to rain within one month. Despite a long period of temporal overlap (81% overlap) between the budding/flowering activity of Subpilocereus repandus and that of Stenocereus griseus, buds and/or flowers on Stenocereus griseus appeared more than a month earlier than on Subpilocereus repandus.
The effect of plant size on phenology and how anthropogenic disturbance may affect cactus resource availability to nectar-feeders and frugivores were also examined. The larger the individual tree within a species, the more flowers were produced and the earlier the tree started to flower. Thus, the indiscriminate removal of columnar cacti for urban development can drastically affect the timing and availability of resources to threatened pollinators and other nectar-feeders, as well as to frugivores and omnivores.
Two species of columnar cacti, Subpilocereus repandus and Stenocereus griseus, are pollinated on Curacao by two species of glossophagine bats, Leptonycteris curasoae and Glossophaga longirostris (Phyllostomidae). The pollination effectiveness of the two bat species can influence the evolution of this mutualism as well as the immediate availability of resources to frugivores and omnivores. I examined the effectiveness of single-visits by L, curasoae and G. longirostris on fruit-set, seed number, and fruit size for each cactus species. Single visits of L. curasoae produced higher fruit-set and seed number in Subpilocereus repandus than did single visits of G, longirostris, but the differences were not statistically significant, possibly as a result of the small size of the L, curasoae sample. The reverse trends were observed for Stenocereus griseus, Pollination of Subpilocereus repandus by L, curasoae resulted in significantly longer fruits than did pollination by G. longirostris, During the peak of the flowering season, flowers received many visits per night. Fruit size (length, width, total mass, pulp mass) was positively correlated with the number of seeds per fruit. These results indicate that the species of bats visiting cactus flowers, as well as the number of visits to flowers, may affect pollination success, and consequently may affect the carrying capacity of the environment in terms of fruit resources for animals that feed on cactus fruits.
The effectiveness of two bat species as pollinators of two species of columnar cacti on Curacao.
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Two bat species, Leptonyrteris curasoae and Glossophaga longirostris, are the principal pollinators of at least two of the three species of columnar cacti that grow on the semiarid island of Curaçao, Netherlands Antilles. I examined the importance of the cacti in the diets of the bats and found that 85–91 percent of their diet samples contained cactus pollen and seeds. At least 43 percent of the samples from each species contained cactus pollen andlor seeds exclusively. Leptonycteris curasoae consumes nectar and pollen of Ceiba pentandra and Agave spp. at the beginning of the dry season and G. longirostris also consumes a few other plant products in the wet season, but both bat species depend nutritionally on cacti. Female bats give birth to one pup per year, and the periods of parturition and lactation in each species correspond to peaks in the reproductive phenology of the two most abundant columnar cactus species. From personal observations and a review of the literature, I determined that bats were unlikely to fly to the mainland to feed, although L. curasoae may do so. I conclude that the interdependence of bats and cacti is suggestive of coevolution, and that columnar cacti are critical for the survival and persistence of nectar-feeding bats on Curaçao.
In view of their ecological importance and the abundance of threats on a developing Caribbean island, we surveyed the bats of Curaçao, Netherlands Antilles, and examined changes in the populations of seven threatened species over a decade, using previously published data as a baseline for comparison. The most important caves for bats (in terms of species representation and reproduction) were visited yearly, and monthly in 2001. Noctilio leporinus still occurs on the island, but does not appear to be numerous (six observed in 2003). We captured Myotis nesopolus nesopolus, but its roosting sites remain unknown. Leptonycteris curasoae curasoae numbers varied greatly, even within a year, and it may travel to and from other islands and Venezuela. Overall, however, the population of this species on Curaçao seems to be declining (1000 in 1993 and 625 in 2003); the disappearance of this pollinator could have severe consequences for the Curaçao ecosystem. Mormoops megalophylla intermedia is declining as well; in 2003, we counted 403 individuals including 75 pups, from 500 to 600 adults in the 10 previous years, representing a 25–30% decline in 1 year. We estimated the population of Natalus tumidirostris to be 890 in 2003. We also found a group of 60 Pteronotus davyi in Kueba di Ratón in 2003.Glossophaga longirostris elongata (1417 individuals counted) is the only species for which our data indicate relative stability over 10 years; L. curasoae and Mor. megalophylla are declining and other species must be monitored closely. Most caves are disturbed; four major caves require attention for the conservation of the most fragile species. Without immediate attention, Mor. megalophylla, in particular, risks imminent extinction. Despite problems associated with bat counts on Curacao, it is clear that regular surveys are crucial to understand bat populations and their fluctuations in caves, and to allow management responses to declines, particularly for areas undergoing rapid urbanization.