Introduction

Of the 116 mammal species present at La Selva, 67 are bats. Most of these bats (67%) are members of the family Phyllostomidae, or leaf-nosed bats (Janzen and Wilson 1983). Species of phyllostomids feed on such things as blood, animals, pollen, nectar, and fruit. Consequently, they are important as agricultural pests, seed dispersers, and pollinators. The role these bats play in seed dispersal is particularly important for understanding forest regrowth in disturbed areas. To determine the role that these frugivores play in seed dispersal, we compared the percentage of seeds of common secondary species (Piper sp.) to other seeds found in fecal samples of frugivorous phyllostomid bats. Simmons et al. (OTS 92-1) found that the Carollia and Artibeus species that they studied had diets composed of at least 50% Piper sp. To examine the effectiveness of these bats at transporting seeds of secondary growth species, we compared fecal samples directly adjacent to a Piper grove with those captured along a flyway. We expected that the fecal samples of bats collected along the flyway would be more diverse, but would nevertheless contain a large percentage of Piper.

We also examined the parasite load on each bat we captured. Ditchfield (OTS 91-3) and Davidson (OTS 97-3) looked at the influence of sex, species or genus, body size, and locality on the parasite load. Davidson found that body size did not correlate with parasite load, but bats that live in larger social groups (60+) had larger parasite loads. Ditchfield, who examined Carollia and Artibeus, only found a correlation between genus and parasite load; no other factors were found to have a significant effect. However, Ditchfield grouped both Carollia species (the smaller C. castanea and the much larger C. perspicillata) in his analysis. Davidson did not include raw data making review of her data impossible. Consequently, we decided to revisit this question. We hypothesized that bats with larger body weight and those that live in larger social groups would have more parasites.

Materials and Methods

We used 3, 30 denier mist nets each night. On 7/19/99 (referred to as SSE), we netted at the successional plots (see fig. 1). This location is adjacent to 1 – 2 year plots. We placed net 1 35 meters, 20 degrees north of the marker SSE 200 in a stand of older secondary forest. We placed net 2 120 degrees southeast of the marker SSE 250 directly crossing the trail, This location is adjacent to a 4-5 year plot and secondary forest. We placed net 3 on the trail directly by a GIS marker tube 50 meters from the 1 – 2 year plots. This net was located between a plot of 4-5 year growth and a plot of 0-1 year growth.

On 7/20/99, we netted on the STR trail. We placed net 1 at marker STR 300 between a grove of Piper auritum and a grove of Musa. We placed net 2 on a path to a small cabin. The path lies off STR 250 at a grove of Piper auritum. We placed net 3 directly across the STR at marker 200. The weather both nights was cloudy; however, we received some rain at 19:30 on 7/20/99. The moon was a first quarter phase. We opened the nets at 18:40 both nights. The nets were closed at 21:22 on 7/19 and 20:45 on 7/20.

We weighed and sexed each bat. We identified them following Reid (1997). We collected fecal samples either from the bat just after removing it from the net, or from the sample bag. We stored the feces in a plastic tube at room temperature and processed them the following day. We separated seeds by adding distilled water to the sample in a petri dish. We observed the material under a microscope and classified seeds according to morphospecies.

For our parasite survey, we sampled only streblid bat flies. We counted the number of bat flies per bat and attempted to sample as many as possible using either forceps or our hands.

Results

We netted a total of 20 bats between 18:50 and 20:12 on both nights (8 on 7/19 and 12 on 7/20; see Table 1). We captured 12 Carollia brevicauda, 3 Carollia castanea, 2 Artibeus watsoni, 1 Artibeus toltecus, and 2 Desmodus rotundus. We released the 2 Desmodus rotundus immediately after netting and no data were collected on these bats. Three of the C. brevicauda females were pregnant.

We collected fecal samples from all but 4 bats. Overall, 79% of the samples contained Piper seeds and 57% contained non- Piper seeds. Of the fecal samples we collected, those from SSE contained less Piper than those collected at STR (57% to 100%). At SSE, a larger percentage of our samples contained non- Piper compared to STR (71% to 43% ).. Of samples collected at SSE, we determined that 29% contained only Piper, 43% contained only non- Piper, and 20% contained both Piper and non- Piper. Of the samples collected at STR, 57% contained only Piper and 43% contained both. None of the samples contained only non- Piper.

We found streblids on C. brevicauda (average 2.7) and C. castanea (average 1.3). The males of C. brevicauda had an average of 3 streblids compared to 2 for the females. The pregnant individuals of C. brevicauda had 2 or fewer streblids. Of the three samples of C. castanea, the females contained more streblids than the males. No streblids were found on A. watsoni or A. toltecus.

The data is presented in Table 1.

Discussion and Conclusions

Our prediction that the diet of bats collected along the flyway would be more diverse than the diet of bats collected near a stand of Piper spp., a secondary growth plant, was supported by our data. 71% of the flyway (SSE) samples contained seeds other than Piper, whereas only 43% of the samples collected near the Piper stand (STR) contained other species. Our data proved how important bats are to dispersing secondary growth plants because so many of the fecal samples in the flyway contained Piper. However, because we did not identify the non-piper seeds to species, we assumed that these seeds came from "non secondary" plants, it is possible that these seeds were also from secondary species. Consequently, we underestimated the amount of seed dispersal in the area. Our data demonstrates the important ecological role frugivorous species play in our increasingly fragmented ecosystems.

Unlike Davidson (1997) and Ditchfield (1991) who concluded that body size is not correlated with parasite load, we found it is. C. brevicauda is larger than C. castanea, A. watsoni, and A. toltecus and it had a greater average of streblid bat flies. Social structure also may influence parasite infestation. Artibeus is less gregarious than Carollia (Ditchfield 1991) which supports our finding that no Artibeus had streblids while all Carollia did. One comparison we were not able to make was between bats of the same size as C. brevicauda but with a different social structure. Consequently, we were not able to conclusively determine whether body size or social structure is more influential over parasite infestation.

We did not sample enough bats to support suggestions that gender or pregnancy affects parasite load.

Literature Cited

Davidson, Susan M. 1997. Ecto parasite load on bats (Order Chiroptera) at La Selva Biological Station. OTS Coursebook 97-3. pp. 258-261.

Ditchfield, A.D. 1991. Bats, bats and more bats: the saga continues. OTS Tropical Biology 91-3, pp. 353-358.

Janzen, D.H., and D.E. Wilson. 1983. Mammals. In: Costa Rican Natural History. Edited by D.H. Janzen, University of Chicago Press. pp. 426-442.

Reid, F. 1997. A field guide to the mammals of Central America and southeast Mexico. New York: Oxford.

Simmons, N. 1992. Bats as Dispersers of Seeds at the Pasture/Forest Boundary. OTS Tropical Biology 92-1, pp. 134-135.

Table 1.
 

Date	Species	Gender	FA (mm)	Mass	Streblids	Fecal Content
7/19/99	C. castanea	M	36.5	13	1	Piper sp. A; Sp. 1
7/19/99	C. brevicauda	M	41	23	6	Piper sp. B
7/19/99	C. castanea	F	36.5	13	2	Sp. 2
7/19/99	C. brevicauda	F	37	14	1	Piper sp. C Markea sp. Sp. 3
7/19/99	C. brevicauda	M	41.5	19.5	0	Sp. 4
7/19/99	C. brevicauda	M	43	22	5	Piper sp. C
7/19/99	C. castanea	M	37	12	1	Undetermined
7/19/99	C. brevicauda	F	39.5	19	3	Sp. 4
7/20/99	A. watsoni	M	38	12	0	Piper Sp. D
7/20/99	C. brevicauda	F	41	16	4	none
7/20/99	C. brevicauda	M	42	16	2	Piper Sp. F Sp. 5
7/20/99	C. brevicauda	F (p)	40	17	2	none
7/20/99	C. brevicauda	M	40.5	17	4	Piper Sp. E
7/20/99	A. toltecus	M	40	22	0	Piper Sp. A
7/20/99	C. brevicauda	F (p)	43.5	27	0	Piper Sp. D
7/20/99	C. brevicauda	F	45	24	4	Piper Sp. F Sp. 6
7/20/99	A. watsoni	F	40	14	0	none
7/20/99	C. brevicauda	F (p)	41	21	1	Piper Sp. A Sp. 7
(p) indicates pregnancy

Relevance to the Classroom

It would be possible to have our students participate in a similar project by connecting with a local nature center or organization that is involved in netting bats such as your local branch of the National Wildlife Federation. It is important to note that bat handling must be done by a trained person as it requires careful techniques. In addition, the handler must be vaccinated for rabies. The direct hands-on experience with these creatures and their ecological role would be invaluable to students at any level.

In completing this project, we were able to experience what it is like to be a student in an inquiry-based process. We have gained much insight into ways that inquiry-based projects can be presented and approached. The OTS "50 Questions" technique, which allows students to ask questions about everything they observe is a technique that can be used at any level with any science topic. Teamwork together with an inquiry approach brings togetherness in moving toward an objective. Students take responsibility and ownership for their project, and learn from each other. Also, inquiry based learning provides kinetic experiences so that we can provide input for those who are kinetic learners. It offers an approach to meet the multiintelligences of all our students. Having been part of an inquiry-based project, we will be better able to understand the frustrations our students might feel at times and be able to provide better support through the process. In addition, we gained increased comfort with field work and discovered that it is possible to learn a lot about a subject in a short period of time. We have had direct experience with research in the rainforest, which we believe will bring enthusiasm and relevancy to our teaching.

Environmental Science courses include content about biodiversity, deforestation and symbiosis, all of which are addressed in this activity.