Guanacaste Province Research Articles

Cave Colonization by Fish: Role of Bat Predation

Freshwater fishes found in a tropical pool regularly enter a subterranean source of water. They do so mostly when fishing bats are active in the evening. If fish are experimentally attracted to the pool during this period, fishing bat activity increases. Laboratory studies demonstrate that avoiding open areas in the evening is characteristic of these fishes. Predation by fishing bats can be a selective pressure favoring cave dwelling, an alternative hypothesis on the origin of cave colonization to entrapment and directional evolution. INTRODUCTION Although many examples exist of obligate (troglobitic) and facultative (troglophilic) cavernicoles for which a surface (epigean) ancestor can be presumed, the origin of cave colonization remains puzzling. Some theories of the evolution of cave populations assume accidental entry into caves followed by permanent entrapment of the organisms. Others propose some directional (regressive) evolution on the assumption that cavernicolous animals represent dying phylogenetic lines which seek refuge in caves (see Barr, 1968, for a review of these theories). Neither assumption has experimental confirmation. A ubiquitous freshwater teleost, Astyanax fasciatus mexicanus (Characidae), is frequently cited as an example of cave adaptation from an epigean ancestor. It is found as an eyed and pigmented surface form and as a blind and depigmented cave one. Although Hubbs and Innes (1936) described the cave form as a new genus and species (Anoptichthysjordani), breeding experiments (Peters and Peters, 1973; Sadoglu, 1957), as well as cytogenetic (Kirby et al., 1977) and electrophoretic studies (Avise and Selander, 1972), indicate that these two forms are conspecific. These forms differ not only in their morphology but also in their behavior. In contrast to the behavior of the eyed form, the blind one does not school, lacks periodic activity cycles (i.e., does not have rest periods like the epigean one), is not aggressive and, although it produces an alarm substance, does not react to it (Breder, 1943; Pfeiffer, 1966; Schemmel, 1980). Several species of tropical bats capture fish such as Astyanaxfasciatus from surface waters (Bloedel, 1955; Reeder and Norris, 1954). The echo-locating Noctilio leporinus, for example, is known to prey on A. fasciatus and on the cichlid Cichlasoma urophthalmus (Simmons et al., 1979; Suthers, 1967; Villa-R., 1966). The distributions of N. leporinus and A. fasciatus are very similar, the former ranging from central W Mexico to Argentina, the latter from southwestern USA to Argentina. At the beginning of the wet season (May) of 1982, I studied a two-species assemblage of about 120 fishes, ca. 60% Astyanax fasciatus and 40% the poeciliid, Brachyraphis rhabdophora. This assemblage colonized a shaded pool, fed by subterranean waters, that was constructed in 1976 close to La Hacienda de Palo Verde, Guanacaste Province, Costa Rica. Diurnal observations on these fishes suggested that both species show an affinity for the subterranean habitat, evidenced by their behavior and distribution. Both species carry food into the subterranean cavity prior to eating it (Romero, 1984). Casual observations indicated that fishes move into the subterranean source of water at dusk the time that fishing bats begin foraging (Bloedel, 1955)and that they reappear in the pool after the bats cease flying over it. METHODS AND RESULTS To examine whether the subterranean cavity serves to protect fish during the time

Pollination by Deceit in a Mass-Flowering Tropical Tree Plumeria rubra L. (Apocynaceae)

Flowers of Plumeria rubra, a mass-flowering tropical tree, share many traits with hawkmoth-pollinated flowers, and Plumeria pollen was recovered from the tongues of 17 hawkmoth species in Costa Rica. Rates of visitation and fruit set were exceptionally low compared with other hawkmoth flowers sympatric with Plumeria, apparently because Plumeria flowers produce no nectar reward. Hawkmoths in a flight cage quickly learned to avoid nectarless Plumeria flowers, but readily fed from these flowers after artificial nectar was added. Although no specific model for Plumeria was found in Costa Rica, the presentation of generalized odor and visual cues that mimic typical hawkmoth flowers may facilitate deceitful pollination of Plumeria. FLORAL MIMICRY ENCOMPASSES a diversity of reproductive strategies used by plants to achieve pollination by animals (see reviews of Wiens 1978, Little 1983). Because of experience with a model, pollinators visit a floral mimic expecting a reward. However, the mimic provides no reward and pollination occurs through deceit. Despite the importance of floral mimicry as a reproductive strategy, little detailed information about such systems exists (Wiens 1978, Williamson 1982, Little 1983). Williamson (1982) stressed that floral mimicry should be defined in terms of reproductive fitness. However, showing that fitness of a floral mimic is increased by its interaction with a model has rarely been successful in floral mimicy systems (Boyden 1980, Bierzychudek 1981, Williamson, pers. comm.). The essential difference in selection pressure on floral and insect mimics suggests that floral mimics may be less dependent upon resemblance to a model than insect mimics. Failure of an insect mimic to deceive a predator usually leads to the mimic's death, but failure of a floral mimic to deceive a pollinatory only results in the loss of potential pollination event. Deceitful plants may also attract pollinators by presenting cues that the pollinators innately recognize, rather than relying on strong resemblance to a model. In some instances a specific model may be absent (Dafni and Ivri 1981a, b; Ackerman 1981, 1983). In addition, convergence within floral syndromes may further complicate analysis of floral mimicry systems (Brown and Kodrik-Brown 1979, Williamson and Black 1981, Little 1983). In this paper I describe the floral biology of Plumeria rubra L. (Apocynaceae), a tropical tree apparently adapted for hawkmoth pollination. Plumeria produces no floral nectar and may be a generalized mimic of other hawkmoth-pollinated flowers. The reproductive biology of this species differs from typical examples of floral mimicry in that Plumeria lacks a specific model, is a massively flowering tree with an extended blooming period, and may be the most abundant hawkmoth flower in tropical deciduous forest of Costa Rica during much of its blooming period. STUDY SITES AND METHODS From 1976-1982 I studied Plumeria in northwestern Costa Rica (Guanacaste Province) at Hacienda La Pacifica, 10 km north of Canias, and at the Comelco ranch, centered 10 km north of Bagaces. The lowland deciduous and evergreen riparian forests at these sites (50-100 m elevation) are described by Frankie et al. (1974, 1983), Opler et al. (1980), and Opler (1983). I also made observations near the community of Monteverde (northern Puntarenas Province) from 1979-1982 where Plumeria grows in semi-deciduous, moist forest on the Pacific slopes at 800-1200 m elevation. FLORAL BIOLOGY.-Flowering phenology is based on Frankie et al. (1974) and my observations from 19761982. I studied the floral behavior of Plumeria using the methods of Haber and Frankie (1982) and Frankie et al. (1983). I monitored nectar secretion intensively on bagged flowers of two trees over several days and checked for possible nectar production on about 20 additional trees by probing flowers with microcapillary tubes and inspecting dissected flowers. I counted ovules in dissected flowers and seeds in mature fruits from the lowland site. Fruit numbers were easily observed on leafless trees during the dry season at

Hummingbird pollination ofMalvaviscus arboreusin Costa Rica

Abstract Malvaviscus arboreus is a self-compatible shrub or small tree native to Costa Rica. Floral morphology, nectar flow pattern, and observations of visitor behaviour, all indicate that flowers are specialised for hummingbird pollination. The principal pollinator in Guanacaste Province during the dry season was the cinnamon hummingbird (Amazilia rutila); numerous other flower visitors removed nectar and pollen but only hummingbirds effected pollination. Anthers have dehisced and stigmas are receptive by dawn, and flowers function for a single day, although the corolla may persist for two days before abscission. Peak nectar production occurs in the early morning coinciding with highest visitation rates of pollinators. Pollen grains are large and linked by viscin threads which probably aid in pollen transport. About 50% of flowers set fruit; the fleshy fruit usually contain three or four seeds and are probably dispersed by birds. Dispersal of pollen and fruit by birds gives a large neighbourhood size co...

Mechanical Abrasion and Intercrown Spacing

The crowns of neighboring trees of similar height do not interdigitate but rather are generally separated by spaces called gaps. In a black mangrove (Avicennia germinans) forest in Costa Rica, the width of crown shyness gaps was positively correlated with the distance pairs of trees or branches adjacent to the gap swayed in the wind (n = 22; p< .01). Abrasion of buds, leaves and branches due to trees knocking into one another seems to create and maintain the spaces around each tree crown. INTRODUCTION Though recent studies of forest structure and dynamics have focused on large gaps caused by single and multiple treefalls, most openings in forest canopies are extremely small (e.g., Hartshorn, 1978; Runkle, 1982). Small gaps usually remain open for a short time, being temporarily closed by branch movements during winds and permanently closed by lateral growth (e.g., Runkle, 1982). However, in some forests light penetrating into the canopy forms a persistent and striking border around individual crowns that are visible from the ground (Fig. 1). The term (from Lane-Poole, 1927-1944, cited in Jacobs, 1955) refers to these leafless regions between adjacent crowns of similar height. Much of the light reaching the understory as sunflecks passes through crown shyness gaps. These openings may also be important insofar as they restrict intercrown movements of arboreal animals and vines (Putz, 1982). A similar sort of defense by mechanical abrasion of competitors and dislodgement of herbivores has been observed in wave-swept algae (Velimirov and Griffiths, 1979). Two theories have been proposed to explain how crown shyness gaps are formed and maintained. One view is that abrasion of buds on wind-blown branches leads to open spaces between tree crowns (Tarbox and Reed, 1924; Jacobs, 1955; Richards et al., 1962). Ng (1977), on the other hand, proposed that crown shyness in Malaysian dipterocarps (Dryobalanops aromatica and various species of Shorea) is caused by reduction in lateral growth due to mutual shading. We tested the hypothesis that crown shyness is caused and maintained by the mechanical abrasion of branches swaying in the wind. Specifically, we predicted that if mechanical abrasion causes crown shyness, then flexible trees and branches should be more widely separated than rigid trees and branches. STUDY SITE AND METHODS We studied crown shyness in an approximately 50-ha stand dominated by Avicennia germinans in the Parque Nacional de Santa Rosa, Guanacaste Province, Costa Rica (10035 'N, 85085 'W). The forest floor is inundated with sea water only when the tides

Flower and Fruit Movements in Muntingia calabura: A Possible Mechanism for Avoidance of Pollinator-Disperser Interference

Muntingia calabura produces a few flowers each day throughout the year. The flowers are usually borne in fascicles of two or three, and within each fascicle, four to nine days separate the sequential opening of individual 1-day flowers. Phyllotaxy is distichous on more or less horizontal branches and the tree architecture conforms to Troll's model. The continuous and regular growth pattern, with frequent branching, facilitates continuous initiation of supra-axillary flowering fascicles. Flowers are pollinated above the branches by bees, and fruit is dispersed from below the branches by bats. By elongation and erection of the pedicel, buds are raised into a flowering position, and following pollination, young fruit are lowered to a position for dispersal. As these movements of reproductive structures allow for pollination and dispersal simultaneously from different positions, it is suggested that for a continuously flowering species this may be a mechanism whereby pollinator-disperser interference is avoided. ALTHOUGH EXTENDED FLOWERING IS NOT UNCOMMON among tropical plants (Frankie et a/. 1974, Bawa 1983), continuous flowering, in the strict sense, is rare (Janzen 1967, Halle et a/. 1978). Continuous, as opposed to rhythmic, growth allows for continuous initiation of inflorescences but does not necessarily imply continuous flowering (Halle et a/. 1978). Likewise, continuous flowering does not preclude episodic fruit maturation. For those few species which continuously produce flowers and mature fruits, it is of interest to know, first, how continuous flowering is achieved, and second, what adaptations allow simultaneous pollination and fruit dispersal. MATERIALS AND METHODS Muntingia calabura L. (Elaeocarpaceae) is a small tree of disturbed successional habitats and is widely distributed in lowland Central America. The species has an unusual sexual system: all trees are similar, but flowers vary continuously in stamen number and ovary size within trees (Bawa and Webb 1983). The flowers are arranged in small fascicles, and those which open first in 2-flowered fascicles, and first or second in 3or more flowered fascicles, usually have a well developed pistil, few stamens, and they usually set fruit. Those flowers which open last in 3or more flowered fascicles usually have many stamens and a small pistil; these flowers usually abscise shortly after blooming (Bawa and Webb 1983). Data for this paper were gathered at Hacienda La Pacifica, five km northwest of Canias, Guanacaste Province, Costa Rica, during the 1981 dry season. At this locality, M. calabura is common in disturbed areas and along the margins of waterways and riparian forest. The climate and vegetation of the area are described in detail by Janzen (1967), Holdridge et al. (1971), Daubenmire (1972), and Frankie et a/. (1974). Initially, in order to observe the phenology of individual fascicles, five 3-flowered and three 2-flowered fascicles were tagged on a single tree and the days on which individual flowers opened were noted. During this study a sequence of bud, flower, and fruit movements was observed, so 10 more flowering fascicles were tagged on each of three trees. Two of these trees were in dry habitats and initiated mostly 2-flowered fascicles. The other tree, in a wet situation, had mostly 3-flowered fascicles. The orientation of each bud, flower, and young fruit relative to the branch and leaves was recorded daily for each of these 30 fascicles. Records were started when the first flower of a fascicle opened and continued until the tagged fascicle had finished flowering and the next fascicle on that branch had begun to flower. The rate of fascicle production, and its integration with vegetative growth, was documented for the three trees. Phyllotaxy, leaf fall, and branching pattern were

Natural History and Acoustic Behavior of a Gregarious Cricket

The cricket Amphiacusta maya (Gryllidae: Phalangopsinae) was studied in the field in Costa Rica and in the laboratory. In the seasonal habitat of Guanacaste Province, C.R., adults are found only during the first 4 months of the rainy season. Adults and subadult nymphs form aggregations each dawn and disperse at dusk. Within the aggregations, males chirp, fight other males, and occasionally mate with females. The acoustic behavior of these crickets differs from that of the better-known field crickets in three major ways. First, males do not produce a calling song. Second, the chirps given in aggressive and courtship contexts are nearly indistinguishable spectrally and temporally. Third, the species-typical chirp does not elicit phonotaxis in adult females or in nymphs. Possibly the calling song would no longer provide a selective advantage to males because females are in their vicinity regardless of male behavior. Additionally, acoustic signal similarity may be a result of selection for aggressive signalling in both contexts (aggression and courtship). Thus these modifications in acoustic signals may be adaptations to a gregarious mating system.

An antifungal terpenoid defends a neotropical tree (Hymenaea) against attack by fungus-growing ants (Atta).

Foragers of the leafcutting ant, Atta cephalotes L. (Formicidae, Attini) seldom or never attack many of the plant species available to them in nature. In the semideciduous forests of lowland Guanacaste Province, Costa Rica, one of the tree species seldom cut is Hymenaea courbaril L. (Leguminosae, Caesalpinioideae). We tested the hypothesis that this species is avoided by the ants because of the presence of ant-repellent secondary compounds in the leaves. A bioassay to test repellency of leaf extracts was developed to guide the chemical isolation of ant repellents, using a laboratory colony of Atta cephalotes.The presence of one or more extractable ant repellents was quickly demonstrated. Subsequent chemical isolation and identification revealed that there was essentially only one terpenoid responsible for the repellency: caryophyllene epoxide. Tests with a concentration series of the pure compound demonstrated that the natural concentration of this terpenoid in Hymenaea could fully account for the observed repellency of intact leaves. Field bioassays of the terpenoid in Costa Rica confirmed this result; leaves of a preferred species, Spondias purpurea L. (Anacardiaceae), became as repellent as Hymenaea leaves when treated with caryophyllene epoxide at natural Hymenaea leaf concentrations. Repellency of the epoxide was 20 times greater than that of caryophyllene, its sesquiterpene hydrocarbon precursor, which is also found in Hymenaea leaves.Attine ants cut leaves to serve as substrate for culturing a specific fungus for food, principally for their larvae. A reasonable hypothesis is that these ants selectively avoid plant species whose leaves contain compounds which are toxic to their fungus. We tested caryophyllene epoxide for antifungal activity and found that it is an extremely potent compound, not only against the attine fungus, but other fungi as well. We speculate that many of the other plant species avoided by these ants in nature may be similarly protected from ant attack by antifungal compounds in their leaves. We further suggest that plant defense against leafcutting ants may be largely an incidental byproduct of selection for fungal resistance in plants.

Fig-Seed Predation and Dispersal by Birds

Observations of birds eating the figs of a single Ficus continifolia (H.B.K.) tree in Costa Rican lowland deciduous forest indicate that a crop of ca 100,000 figs was exhausted in five days, of which 95,000 were removed during the first three days. Birds processed an estimated average of 20,828 figs/day (65. 1% of the total daily consumption), and the difference (34.9%) represented fruits consumed by mammals and/or those falling to the ground. Parrots were responsible for 78 percent of the total taken by birds and 50.6 percent of the figs leaving the tree per day. Use by these seed predators represents fruit (and seed) waste. The true avian dispersers (e.g., orioles, tanagers, trogons, flycatchers) took only ca 4600 figs/day. An estimated 4.42 X 106 fig seeds were lost each day, 36.2 percent of them to parrots and 63.8 percent to destruction by invertebrates (mostly agaonid wasps). Only 6.3 percent of the seeds leaving the tree per day are actually dispersed undamaged by birds. FIGS HAVE LONG BEEN RECOGNIZED as an important food for vertebrate frugivores in tropical habitats (Hladik et al. 1971, Leck 1972, Fleming et al. 1977, Bonaccorso 1979). In spite of being a prominent element in tropical woody vegetation, the relative contribution of the various consumer organisms to the seed shadow is poorly known (Janzen 1979b). I report here observations of birds eating the fruits of a single Ficus cotinifolia (H.B.K.) tree in the lowland deciduous forest of Santa Rosa National Park (Guanacaste Province, Costa Rica). A description of study area may be found in Fleming et al. (1977). The study tree was located close to the park's access road, on the border between a dry-deciduous forest stand and a large area covered with African pasture grass, Hyparrhenia rufa, Stapf., and scattered shrubs (e.g., Acacia collinsii, Safford; Eugenia sp.). The tree was 10 m high, and horizontal crown protection was approximately 15 m in diameter. At the time of observation, the crown was leafless and bore numerous figs. New leaves started to flush when the fig crop had been exhausted by frugivores.

Ecological Distribution of Chlorophyllous Developing Embryos among Perennial Plants in a Tropical Deciduous Forest

Ecological Distribution of Chlorophyllous Developing Embryos among Perennial Plants in a Tropical Deciduous Forest

Variation in Average Seed Size and Fruit Seediness in a Fruit Crop of a Guanacaste Tree (Leguminosae: Enterolobium cyclocarpum)

A detailed examination of the ordinary 1980 fruit crop of an ordinary large adult guanacaste tree (Enterolobium cyclocarpum) in Guanacaste Province, Costa Rica (1980) shows that for fruits with about 6-16 seeds (range, 1-18 seeds per fruit) there is about ***1 g dry weight fruit tissue per seed (seeds averaging about 820 m each). Fruits that have about 1-5 seeds on average have 1.5-3 times as much dry fruit tissue per seed as do the seed-rich fruits, and also contain seeds that weigh about 8% more on average than the seeds in the seed-rich fruits. The average seed weight per fruit was found to decrease slightly if all sizes of fruits are considered, but to remain essentially constant over the range of 7-16-seeded fruits. This category contained 78% of the fruits. These findings suggest that different parts of the seed crop may end up in different dispersers and dispersers with different preferences for fruit seediness and tolerances for seed size may remove different portions of the seed crop.

VARIATION IN AVERAGE SEED SIZE AND FRUIT SEEDINESS IN A FRUIT CROP OF A GUANACASTE TREE (LEGUMINOSAE: ENTEROLOBIUM CYCLOCARPUM)

A detailed examination of the ordinary 1980 fruit crop of an ordinary large adult guanacaste tree (Enterolobium cyclocarpum) in Guanacaste Province, Costa Rica (1980) shows that for fruits with about 6‐16 seeds (range, 1‐18 seeds per fruit) there is about ***1 g dry weight fruit tissue per seed (seeds averaging about 820 m each). Fruits that have about 1‐5 seeds on average have 1.5‐3 times as much dry fruit tissue per seed as do the seed‐rich fruits, and also contain seeds that weigh about 8% more on average than the seeds in the seed‐rich fruits. The average seed weight per fruit was found to decrease slightly if all sizes of fruits are considered, but to remain essentially constant over the range of 7‐16‐seeded fruits. This category contained 78% of the fruits. These findings suggest that different parts of the seed crop may end up in different dispersers and dispersers with different preferences for fruit seediness and tolerances for seed size may remove different portions of the seed crop.

A New Species of Cyperus (Cyperaceae) from Costa Rica and Mexico

Cyperus herndoniae is described, illustrated, and compared to its nearest relative, C. distans. It is known from collections from Guanacaste Province, Costa Rica, and Chiapas, Mexico. During the course of my work on Cyperus in Costa Rica and Panama, an undescribed species was noted from two collections made by R. L. Wilbur in Guanacaste Province. Later, a third collection made by D. E. Breedlove in Chiapas, Mexico, was detected. Cyperus herndoniae Tucker, sp. nov., fig. 1.-TYPE: Costa Rica, Guanacaste, local in ditch at the entrance of the Santa Rosa National Park, 21 Jul 198 1, Wilbur 31825 (holotype: DUKE; isotypes: CR, F, GH, MO). Rhizoma ascendens, ad 2 cm longa. Radii simplices. Spiculae linearilanceolatae, 8-16 mm longae, 1.5-2.1 mm latae. Squamae divaricatae, ellipticae, 3-3.2 mm longae, 1.5-1.9 mm latae. Achaenium trigonum, oblongum, 2-2.2 mm longum, 0.6-0.7 mm latum. Affinis Cypero distanti L.f. Culms single or 2-3 together, 30-75 cm tall, trigonous, smooth; basally indurate. Rhizomes up to 2 cm long, turning upward. Roots fibrous. Leaves 1-4, 20-40 cm long, 2-3 mm wide, margins scabrellate. Inflorescence bracts 3-6, 2-25 cm long, 1-6 mm wide, borne horizontally, margins scabrellate. Rays (4-)6-8, up to 5 cm long, unbranched. Spikes ovoid to hemispherical, (5-)15-35 mm long, 17-45 mm wide; rachis 3-12 mm long. Spikelets (10-)25-50 per spike, linear-lanceolate, compressed, 816 mm long, 1.5-2.1 mm wide; rachilla slightly flexuous, its wings hyaline, 0.3-0.4 mm wide. Scales 4-12 per spikelet, elliptic, 3-3.2 mm long, 1.3-1.9 mm wide, obtuse, mucronulate, borne divaricately on the rachilla, laterally 2-3-nerved, brown to stramineous, the margins hyaline, the keel 3-nerved, greenish. Stamens 3; filaments ribbonlike, 3.5-4 mm long; anthers oblong, 0.9-1.1 mm long. Styles 0.4-0.7 mm long; stigmatic branches 3, 2.5-3 mm long. Achenes trigonous, oblong, 2-2.2 mm long, 0.6-0.7 mm wide, apiculate, slightly stipitate, angles rounded, faces flat to slightly convex, finely papillose, brown. Distribution. Roadsides, wet marshy depressions, and low flats from sea level to 700 m. Flowering and fruiting specimens have been collected in Jul, Aug, and Sep. Specimens examined. Costa Rica. Guanacaste: just outside Santa Rosa National Park, Wilbur 30970 (DUKE); 14 km S of La Cruz, Wilbur 30928B (DUKE); about 18 km N of

The Pattern of Colonization of Epiphytes on Calabash Trees (Crescentia alata HBK.) in Guanacaste Province, Costa Rica

We examined the structure of the community of epiphytes growing on Crescentia alata trees in Santa Rosa National Park, Costa Rica. Four orchid species were dominant in this community, showing a distinct order of colonization of the calabash trees, with Oncidium cebolleta colonizing first, Encyclia cordigera second, Brassavola nodosa third, and Laelia rubescens fourth. We were unable to find any differentiation of the locations of these species based on the physical characteristics of the sites. It is hypothesized that the colonization pattern observed is due to the quantity of propagules produced by each species. THE NUMBER OF SPECIES found in a community is determined by five major factors-the time for colonization, the distance over which colonizers must travel, the number of potential colonizers, the size of the area to be colonized, and the biotic interactions between colonizers (MacArthur and Wilson 1967). Two approaches have been used to determine the effects of these factors upon the community organization of oceanic islands (e.g., Diamond 1969, Simberloff and Wilson 1969) and a variety of island-like situations (e.g., Vuilleumier 1970, Brown 1971, Culver, Holsinger, and Baroody 1973, Opler 1974). One approach applied to both plant (Johnson, Mason, and Raven 1965) and animal (Hamilton, Barth, and Rubinoff 1964, Wilson and Taylor 1967) communities has been to use correlative techniques to describe the patterns of species number and distribution from to on a large geographical scale. The second approach, applied exclusively to animal communities, has been to manipulate the five factors experimentally (e.g., Simberloff and Wilson 1969, Addicott 1974, Schoener 1974). In this paper we describe the community structure of plants occurring on a local scale using correlative techniques and suggest that this system is one in which experimental work on the relative roles of these five factors in determining community structures may be performed. STUDY AREA AND METHODS Individual Crescentia alata HBK, the calabash tree (Bignoniaceae), constitute an island-like situation for epiphytic plants. The calabash tree is an ideal epiphyte host because its soft, deep bark provides easy anchorage for epiphytes and recess for humus accumulations (Pittendrigh 1948). The study site, a 10 ha calabash orchard in Santa Rosa National Park, Guanacaste Province, Costa Rica, has been described by Janzen et al. (1980). It is surrounded by dry, deciduous thorn-forest, the dominant vegetation type in this region (Holdridge 1967). No individual calabash tree at this site is located more than 100 m from the edge of the thorn-forest. The spherical canopies of the calabash trees range from 0.5 to 7.5 m radius. Since trees are spaced at least 5 m apart, canopies of individuals rarely intertwine. Each calabash tree was considered an island which may be colonized by epiphytic plants: one cactus species, three bromeliads, and five species of orchids. Nomenclature is that of Janzen and Liesner ( 1980). We measured the canopy radius of a randomly chosen calabash tree and recorded the species of epiphytes present (sample sizes are indicated in figure 1). Canopy radius was used because it was both easily measured and accurate with repetition. The existence of a species-area relationship was investigated by means of regression analysis using a logarithmic curve fit after making a scatter plot of the data. To explore the temporal pattern of colonization, we calculated the percent occurrence of each epiphytic species in one-species, two-species, three-species, etc. communities. To study the role of biotic interactions, we contrasted the relative abundance of each epiphytic species on small trees (less than 2 m canopy radius) with that on large trees (greater than 4 m canopy radius). To obtain these numbers, at least two branches were randomly chosen on a minimum of five inBIOTROPICA 14(2): 137-14

Patterns of Herbivory in a Tropical Deciduous Forest

In the lowland deciduous and riparian evergreen forests of Guanacaste Province, Costa Rica, the insect seed predators are highly host-specific and display a variety of traits suggesting that the ways they use hosts are not randomly distributed. The vertebrate seed predators may feed on many species of seeds over the course of a year or within the animal population, but, at any one time or with any one individual, strong facultative host-specificity occurs. Furthermore, the vertebrates have a variety of species-specific behaviors that suggest specialization to overcome the defenses of particular seed species. Even the dispersal agents kill seeds as they pass through their guts, and the details of seed-defecation patterns should be important to the seed. Within this forest, leaf-eating caterpillars seem to be either specialized on one or a few species of plants, or spread over many. While an entire forest is never defoliated at one time, defoliations and severe herbivory occur with many plant species in various seasons or years. Herbivory by large herbivores is probably trivial when compared to that of the insects. Furthermore, the defenses that the large herbivores have to overcome may well have been selected for by both insects and extinct Pleistocene large herbivores. I suspect that many of the animal-plant interactions in this forest are not coevolved, and those that are coevolved will be difficult to distinguish from those that are not. THERE ARE TWO QUITE DIFFERENT KINDS of patterns of herbivory.' First there is the way an individual herbivore bites a plant and the influence of this on other herbivores (Janzen 1973) and on the fitness, health, and growth patterns, et cetera of the bitten plant (e.g., Simberloff et al. 1978; Oppenheimer and Lang 1969; McKey 1978; Chester 1950; Janzen 1976a, b; Rockwood 1973). Much more research is needed on the allocation responses, economics of retention versus shedding of damaged parts, and strategic damage versus absolute damage. For example, the production of induced chemical defenses may raise the fitness of a plant not through the lowering of the absolute amount of herbivore damage done, but rather by causing the damage to be distributed in a manner that harms the plant less (Janzen 1979). However, this essay is not directed at this pattern of herbivory, but rather at the second one. This is the distribution of the species and quantities of herbivores across the mosaic of plant species, developmental stages, plant parts, habitats, defense types, and time. I focus on this pattern of herbivory in the deciduous forests, and their contained riparian vegetation and old pastures, in Santa Rosa National Park (SRNP), northwestern Guanacaste Province, Costa Rica (0-300 m elevation). INSECT SEED PREDATORS The lowlands of Guanacaste Province exclusive of the Nicoya Peninsula (about 3200 kiM2) have about 975 species of broad-leafed plants at latest count (Janzen and Liesner 1980). In an ongoing study of the insects that eat the seeds of these plants, at least 110 species of beetles (Bruchidae, Curculionidae, Cerambycidae) were reared from more than 3700 samples of fruits and seeds (Janzen 1980a). The seeds of at least 100 of the 975 species of plants were regularly found to have beetle larvae seed predators that develop in the seeds at the stage between nearly full-sized and mature (preand post-dispersal). Most of the species of beetles were specific to a particular plant species: 83 species (75%) preyed on one plant species, each of 14 preyed on only two, nine on three, and two on four. The bruchid Stator pruininus preyed on six species and Stator limbatus on eight species, and there was no overlap in their two prey lists (although all prey were legumes). Of the 100 prey species, 63 were in the Leguminosae, and the remainder were spread among 17 other plant families; however, only 17 percent of the broadleafed plant species in the Guanacaste lowlands are

Breeding Habits of the Toad Bufo coccifer in Costa Rica, with a Description of the Tadpole

-The breeding habits of Bufo coccifer were studied in northwestern Costa Rica between 1971 and 1974. This species breeds during the rainy season, at least from May through August. Males chorus from areas of shallow water. Their calls resemble those of Mexican representatives of the species in pulse rate and duration, but are closer to those of other Costa Rican and Panamanian populations in dominant frequency. Thus, our data do not clearly support recognition of Bufo cycladen as a distinct species for the Mexican populations. Amplexus is axillary, and two strings of eggs are extruded simultaneously during oviposition. Tadpoles, described for the first time in this paper, are secretive and do not aggregate. Development to metamorphosis requires about 5 weeks. Bufo coccifer Cope is a medium sized toad known from localities primarily along the Pacific versant of Mexico and Central America from sea level to about 2000 m elevation (Zweifel, 1965; Porter, 1964a, 1965; Meyer and Wilson, 1971). The mating calls of the Mexican and Central American populations of Bufo coccifer differ (Zweifel, 1965; Porter, 1965). These vocal characteristics, together with slight morphological differences, were used to justify recognition of the Mexican populations as a distinct species, Bufo cycladen (Lynch and Smith, 1966). Porter (1967) argued that Bufo cycladen was a nomen dubium. Although Smith and Smith (1976) recognized the distinctness of the Mexican populations, little information has been published on the species in the past 15 years. The tadpole has not been described. During the course of our work on the reproductive ecology and behavior of frogs in the Tropical Dry Forest formation of northwestern Costa Rica, we obtained considerable data on the breeding biology of Bufo coccifer. Herein, we report our observations and describe the tadpole of this species. STUDY SITE.-The study area was located on the property of Estaci6n Experimental Enrique Jimenez Nufiez in Guanacaste Province, Costa Rica. This station, owned and operated by the Ministerio de Agricultura y Ganaderia of Costa Rica lies about 13.6 km SW Canfas in a zone of Tropical Dry Forest (Tosi, 1969). General site descriptions of the area exist (e.g., Orians and Paulson, 1969; Holdridge et al., 1971; Sawyer and Lindsey, 1971; Janzen, 1973; McDiarmid et al., 1977). However, these papers refer primarily to the forested regions of the farm, particularly those in riparian areas. Although individual Bufo coccifer occasionally are found in forest habitats, these toads are located more commonly in areas where the forest has been cleared for pasture or cultivation. Observations were made in two types of cleared areas. One was a pasture about 2.4 by 1.0 km located at the base of Cerro Eskameca and adjacent hills (Fig. 1). The somewhat irregular pasture (ca. 10 m elev.) is sown with various introduced forage grasses and supports small weedy herbs (e.g., Compositae, Malvaceae, Euphorbiaceae), vines (e.g., Cucurbitaceae, Leguminosae, Bignoniaceae), small saplings of various forest trees (especially Enterolobium cyclocarpum), and a number of leguminous shrubs. One of the shrubs, Mimosa pigra, grew in dense stands covering large areas. Usually, toward the end of each dry season, the pasture areas were plowed and all surface vegetation was turned under. With the first rains, new grass sprouted, and cattle and horses were turned out to graze. Within the pasture areas three ponds filled in May or June and, except in E SOUTHWESTERN ATURALIST 26(4):353-363 NOVEMBER 20, 1981 This content downloaded from 157.55.39.224 on Wed, 14 Dec 2016 05:03:07 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist FIG. 1.-Irrigation canal (above), flooded pasture (middle), and flooded roadside (below) at Estaci6n Experimental Enrique Jimenez Nuiiez, used as breeding sites by Bufo coccifer. 'LI IIIWI L C-lC1----I 354 vol. 26, no. 4 -....,-'' .,. __M ._liB36 . ^ This content downloaded from 157.55.39.224 on Wed, 14 Dec 2016 05:03:07 UTC All use subject to http://about.jstor.org/terms McDiarmid and Foster-Costa Rican Bufo coccifer

Polymorphic Mimicry of Polistine Wasps by a Neotropical Neuropteran

Climaciella brunnea is a polymorphic mantispid studied in Guanacaste Province, Costa Rica. Five distinct color morphs were sampled, each being a presumed Batesian mimic of a different polistine wasp. The proportion of morphs varied between three separate localities and presumably reflected the differential abundance and aggressiveness of models at each site. Markrelease-recapture studies did not reveal any significant difference in mortality rates between morphs. Frequency-dependent selection via differential predation is probably responsible for the evolution of the polymorphism and would maintain different morph frequencies at different sites. Climaciella brunnea (Say) IS A PREDACEOUS MANTISPID which ranges northward through Central America, Mexico, and the western and central United States. Previous workers have noted that Climaciella individuals closely resemble polistine wasps (Smith 1934, Batra 1972). During studies conducted between 1971 and 1973 in Costa Rica, it was observed that C. brunnea populations were composed of individuals representing five distinct color morphs, each rather closely mimicking and presumably constituting a Batesian mimic of a different polistine wasp. The wasps involved were Polistes instabilis Sauss., P. canadensis (L.), P. carnifex (Fabr.), P. erythrocephalus Latr., and Synoeca sept entrionoalis Richards. This paper describes the mimetic relationships and reports on several experiments to test the existence of frequency-dependent selection which is presumed to maintain the polymorphism in these insects.

Frugivorous Bats, Seed Shadows, and the Structure of Tropical Forests

Frugivorous Bats, Seed Shadows, and the Structure of Tropical Forests

Guanacaste Tree Seed-Swallowing by Costa Rican Range Horses

Guanacaste tree fruits (Leguminosae: Enterolobium cyclocarpum) were fed by hand to seven range horses (Equidae: Equus caballus) in Santa Rosa National Park, Guanacaste Province, Costa Rica. Guanacaste seeds are large and heavy (0.2—0.8 mL and 300—1000 mg) and easily perceived by the horse. The seeds swallowed ranged from 25.1% to 61.5% for different horses. Of the seven horses, four swallowed the same percentage of the seeds in a fruit, over a range in size from five to 18 seeds per fruit. The other three horses departed slightly from a constant percentage of seeds swallowed per fruit. A guanacaste fruit is constructed such that the ratio of fruit to seed stays about the same over a wide range of numbers of seeds per fruit, and therefore this response by the horses is not startling. Why seeds are spit out is discussed. While seed spitting undoubtedly lowers the quality of horses as guanacaste seed dispersal agents, the high frequency of seed spitting does not mean that the horse is necessarily a "poor" dispersal agent.

Swarming Activity of Polybiine Social Wasps (Hymenoptera: Vespidae: Polybiini)

Swarming Activity of Polybiine Social Wasps (Hymenoptera: Vespidae: Polybiini)

Digestive Seed Predation by a Costa Rican Baird's Tapir

Digestive Seed Predation by a Costa Rican Baird's Tapir