Susan Summers, Virginia Living Museum, Newport News, VA

Keith Camburn, West Mecklenburg High School, Charlotte, NC

Karen Temple Beamish, Albuquerque Academy, Albuquerque, NM

Roy Arezzo, City as School, Manhatten, NY

Sharon Parker, Gallatin County HS, Warsaw, KY

Human development of land is the major cause of species decline and loss of biodiversity ( Vitousek, 1994). Even within National Parks, which are set aside as refuges for wildlife, human development such as road construction, and campsite and trail development has created immense pressure on wildlife. Human population continues to expand and visitation to national parks grows at an enormous rate. As Costa Rica’s premier ecological reserve, La Selva Biological Station, increases in research and ecotourism visitations have been substantial. In 1982, La Selva Biological Station hosted 57 researchers and over 7320 guests while by 1991 La Selva’s visitations increased to 257 researchers and 16,000 guests (McDade, et al., 1994). As a consequence of this growth, new construction at the main complex creates noise and disturbance. In addition, human traffic on park trails is growing. An important consideration to the managers of La Selva should be whether or not the heavy human use of trails and construction is impacting the presence of animals living within the park.

La Selva Biological Station, located in San Pedro, Costa Rica, is owned and operated by the Organization for Tropical Studies, a non-profit consortium of universities and research institutions from the United States, Latin America, and Australia. La Selva Biological Station is recognized worldwide as a center for tropical rain forest research and education. This 3,746 acre reserve, which borders Braulio Carrillo National Park, contains an extensive 35-mile trail system. Mammal species native to the reserve total 120 with 67 of those consisting of bats (OTS information handout). During a preliminary 2-day period, observations indicated that many of the trails appeared to be heavily used by a number of mammal species including the Central American Agouti (Dasyprocta punctata) and the Collared Peccary (Tayassu tajacu) as well as bird species.

Many cats, including the Jaguar (Panthera onca), are known to utilize man-made trails at night (Emmons, 1997) and it is felt that other mammals and birds may also utilize these man-made trails at La Selva. Therefore, the purpose of this study was twofold: 1) to determine which animals are diurnally and nocturnally utilizing these manmade trails; and 2) to establish whether a relationship exists between the amount of animal use of man-made trails and the distance of these trails from the main station complex.

Thirteen sampling sites were established along man-made trails within La Selva Biological Station. Each sampling site consisted of a 1 m X 2 m “muddy” area within a “mud” trail or a “muddy” area next to a concrete trail. Each site was chosen based on the presence of mud, absence of obstructions (roots, rocks, etc), and level topography. Sites were avoided that were too sloped or within depressions to ensure that rain and/or high temperatures would not damage the integrity of the mud. At each site the corners of the 1 m by 2 m sampling area were marked with sticks and the ground was prepared using water, a flat board, and a concrete trowel. All trails were over 2 m in width and plots were offset from the center to avoid human traffic. For each site twigs, leaves, and rocks were removed from the sample plot and dry spots and large rocks were covered with 3 cm of mud. The addition of water and the use of the trowel created a relatively flat and uniform mud texture that facilitated animal track identification. Hot temperatures, moderate humidity, and little precipitation characterized both sampling days.

Only prominent and identifiable tracks were used in the data set. In order to determine if a relationship exists between the abundance and diversity of animals using these man-made trails and the distance of these trails from the main station complex, sites were selected from a variety of trails at varying distances from the station. The center point for the La Selva compound was chosen as midway through the

Stone Bridge (see map) which lies between the main commissary and the laboratory facilities. Concentric circles were drawn with a radius of 250 m (Zone 1/near), 500 m (Zone 2/medium), and 1000 m (Zone 3/distant). Zone 1 includes sites 1, 2, 3, and 8. Zone 2 includes sites 4, 5, 6, and 9. Zone 3 includes sites 7, 10, 11, 12, and 13. We chose to place these sampling sites into three categories: Zone 1 is less than 250 m from the center point of the station; Zone 2 lies from between 250 and 500 m from the station; and Zone 3 includes sites from over 500 m from the station. All sampling sites were prepared on the afternoons of July 27^th and 28^th, 2001. Each site was visited on the mornings of July 28^th and 29^th, to determine the types and numbers of animal tracks present. Tracks were identified using Emmons (1997) and Reid (1997). Characteristics used to assess tracks included width, shape, number of toes and other physical characteristics.

Site #1: Site 1 is located on the Soccer Field trail in Zone 1 and is less than 100 m from the main compound and less than 50 m from a soccer field. The dirt trail is 5.2 m wide. The surrounding vegetation is primarily secondary growth with a herbaceous understory. The trail is mostly open and receives direct sunlight.

Site #2: Site 2 is located further along the Soccer Field trail in Zone 1, approximately 200 m from the trailhead. The trail is 3 m wide and surrounded by secondary growth with young trees and light gaps. There is a steep slope on the west side of the trail that runs down to a stream. Approximately 300 m from the site is a small dirt road that leads to a plantation.

Site #3: Site 3 is located on the River Station trail in Zone 1 approximately 50 m from the Laboratory section of the main compound. The trail is 1.2 m wide and and includes a 25 cm wide cement walkway. It is muddy on both sides of the trail and the sampling site was placed in a flat area on the east side of the trail. The vegetation is mixed with some large trees and many heliconia plants. Light penetration is moderate.

Site #4: Site 4 is located on the SOR trail in Zone 2 approximately 150 m from Site 3. The trail is 2.5 m wide with a 60 cm cement walkway in the center. The plot was offset to the eastside of the trail. The vegetation includes mixed palms with some canopy cover and much shading.

Site #5: Site 5 is located on the SOR trail in Zone 2 less than 100 m from Site 4. The trail width is 3 m wide with a 60 cm cement walkway in the center. The plot is off-center to the eastside of the trail and there are many large palms on both sides of the trail.

Site #6: Site 6 is located on the SOR trail in Zone 2 near the 300 m trail marker. The trail is 2.5 m wide and the cement is consistent at 60 centimeters. The plot is offset to the west side of the walkway. The site is surrounded by thick secondary forest with much overhead canopy cover and vines extended over the trail.

Site #7: Site 7 is located on the SOR trail in Zone 3 near the 400 m trail marker. The trail is 3 m wide and contains a 60 cm cement walkway. The sampling site is offset to the west side of the walkway. To the east of the trail is a steep slope with a running stream below. The sampling site is heavily shaded by secondary forest.

Site #8: Site 8 is located in Zone 1 near the CCC trail approximately 5 m southwest from the Cardonnas marsh. The area was very muddy despite the lack of rain. The trail is 2.8 m wide and includes a 100 cm cement walkway. We offset the sampling site to the south side of the walkway. The secondary forest contains both tall trees with many epiphytes and short palms.

Site #9: Site 9 is located on the CCC trail is located in Zone 2 before the 200 m trail marker. The trail is 2.6 m wide with 38 cm blocks comprising a mid-trail walkway. The plot is offset to the south side of the trail. The vegetation is mixed secondary growth forest with some tall trees dispersed among mixed palms and heliconia. The sampling site is approximately 5 m from an upward slope.

Site #10: Site 10 is located on the CCC trail in Zone 3 near the 600 m trail marker. The trail is mostly dirt and has a width of 2.1 m. We set the sampling site to the south side of the trail in a level area several meters before a gradual incline. This site is predominantly primary forest with a tall, thick canopy and many types of palms.

Site #11: Site 11 is located off of the STR trail in Zone 3, near the 500 m trail marker. The STR trail (Sendero Tres Rios), also known as the bike trail, has a large cement path that runs north/south past secondary forest, experimental agriculture plots, and some primary forest. The site, located on an unmarked trail, we choose is 10 m west of the STR trail. The trail is mostly mud with a width of 2.5 m. The vegetation includes secondary growth with mixed palms and thin trees with some light gaps in the canopy.

Site #12: Site 12 is located 10 m off of the west side of the STR trail in Zone 3, near the 800 m trail marker on the CEN trail. The trail is 3.1 m wide and mostly made up of mud and compacted soil. The vegetation is mostly secondary growth with thick canopy.

Site #13: Site 13 is located approximately 100 m off of the east side of the STR trail in Zone 3, near the 800 m trail marker on the SOC trail. The trail is 2.7 m wide and very muddy with thick a layer of secondary growth canopy. There are many heliconia plants in the area.

Results

The data showed a decrease in both number of species and total number of individual tracks as distance from the compound (the source of human disturbance) increased. A total of 12 species were identified including six mammals and five species of birds (Table 1). The most abundant species encountered in terms of both individual and number of tracks were the Central American Agouti and Collared Peccary. Of particular interest was the occurrence at Site 13 of an Ocelot. The number of individuals encountered on July 27, 2001, and July 28, 2001, were 17 and 31 respectively. The total number of species per plot varied from one to five.

In Zone One, located 0-250 m from the La Selva compound, 138 individual tracks were located in the two-day cycle, 77 were located in Zone Two (250-500 m), and 96 tracks were located during the two-day cycle in Zone Three (500-1000 m). The average number of individual tracks per two-day cycle in Zone One was 34. Zone Two and Zone Three both averaged 19 individual tracks. The average number of species identified in Zone One was 2.75. Zone Two contained evidence of 2.5 species, and Zone Three averaged 2.0 species.

Upon initial evaluation of the results, it would appear that the animals of La Selva are not deterred by the presence of human disturbance, but rather, that they are abundant in spite of human occupancy. Both the number of species and the number of individual tracks increased in the zone closest to the compound (0-250 m). We feel that the increased evidence of animals presence could be due to a number of factors, the first being that large predators avoid human contact and thus would avoid the compound. Common large cat prey species such as the Collared Peccary and the Central American Agouti would be opportunistic in taking advantage of this lessened predation. Another possible explanation would be that areas affected by human disturbance create an edge effect that may actually attract animals. The increased foliage commonly accompanying the edge of a human disturbance may create more habitat for some species. Introduced grasses in clearings might serve as preferred food sources for some foraging animals.

However, it could be argued that animals closer to the compound were more acclimated to human exposure. Because the preparation of the mud plots required strong human contact (ever to the extent of smoothing with hand-held trowels), it can be argued that human scent may have deterred animals that are wary of human contact.

If this study were to be repeated, there are certain parameters that would need to be improved. The preparation of the mud plots would need to be standardized to the same consistency. Plots that may have been drier may not have held tracts of smaller animals. We observed small birds walking on a drier plot on which they left few tracks.

The scope of this study might be expanded to consider what effects humans are having on the state and national parks in the United States. Plans for trail expansions, building construction, or clearings for roads should take into consideration the effects of human interference on the normal traffic of animals and their interactions.

In conclusion, this project showed an increase in both numbers of species and animal traffic near the La Selva compound. The effect of human presence on an ecosystem is very complex and this project reflects a simplistic attempt to measure that effect.




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