Effects of Habitat Fragmentation and Modification on Species Richness and Abundance of Anurans Drisana Shanthan
Advisors: Kristen Greaney and Steve Raciti, Department of Urban Ecology, Hofstra University
Results
Introduction During the past few decades, the decline of amphibian populations was noted globally as a rising threat to biodiversity. This threat has persisted, leading to increased research in this area. The decline in amphibian populations has been linked to various factors, including habitat fragmentation, destruction, in part due to roads and highways. Other factors linked to amphibian declines include: ○ Vegetation: A scarcity of vegetation may negatively impact certain species’ ability to inhabit terrestrial habitats, as vegetation is necessary for cover from predation and for breeding (Ray et al. 2002) ○ Habitat Size: Many amphibians were found to be highly sensitive habitat modification (Nowakowski et al. 2016). ○ Aquatic Habitat: Limited access or an insufficient number of ponds may interfere with a species’ ability to reproduce or for larvae to survive (Kolozvary and Swihart et al. 1999). ○ Aquatic Habitat: A lack of water bodies will negatively impact species richness, as many species require both terrestrial and aquatic habitats (Hamer et al. 2016). Multiple factors contribute to amphibian declines and research into which factors, and how they interact, is necessary to improve conservation efforts of these organisms.
Figure 1. Field sites on satellite imagery background from ArcMap 10.7.
Figure 3. Anurans observed per meter in each park. (Total anurans observed in each park was divided by distance surveyed in each park.)
In this study, a low value of species richness was identified (4 identified species, 8-9 expected) with the majority of anurans identified being the generalist species Lithobates clamitans (green frogs) and Lithobates catesbiana (bullfrogs). This may indicate that current habitat conditions are only suitable for generalist species, and less suitable for specialist species, although further surveys would be required to determine this. A positive correlation between the number of water bodies at a site and the number of number of anurans observed supports previous research that suggests larger available aquatic habitat supports more individuals. A positive correlation was between the number of anurans observed and the size of the park, however this was identified after the removal of the outlier of Connetquot park, which is approximately 16 km2, a much larger park than the rest surveyed. A one-way ANOVA showed that there is a.statistically significant difference (p-value=0.0116) between the average number of anurans observed in parks with dense and sparse vegetation types. These results suggest that urbanization on Long Island may have reduced species richness and abundance as a only four species were identified of the 8 or 9 expected, with the majority (98%) of anurans identified as green frogs or bullfrogs. Urbanization reduces aquatic and terrestrial habitat available to anurans and these data suggest that as the number of water bodies increases, the number of anurans present also increases. These data also suggest that as the size of the park increases, the number of anurans present also increases. This study is limited by the number of parks visited and time restrictions; observations across seasons to control for weather conditions and a greater number of sites would be ideal in future studies.
Figure 2. Number of observations by site and species (see Table 1 for site key).
Figure 4. Anurans observed by size of park (R2 = 0.311); Removed outlier of Connetquot park (16km
References
Methods ● Visual surveys were conducted at 15 sites (see Table 1), with several sites re-visited to conduct call surveys for species identification confirmations. During visual surveys, each anuran was identified to the species level, with photographic observations deposited in the citizen scientist app iNaturalist. ● Google Maps and ArcGIS (ArcMap 10.7) were used to measure habitat size, distance surveyed, count number of water bodies in each parkVegetation type (sparse and dense) was ● Finally, data analysis was conducted using Google Sheets XLMiner Analysis ToolPack to calculate linear correlations and a one-way ANOVA.
Discussion
Figure 5. Number of anurans observed versus number of water bodies at a site (R2=0.6423).
Key Observations • Number of species observed: 4 (Lithobates palustris, Anaxyrus fowleri, Lithobates clamitans, Lithobates catesbiana) • Highest number of anurans observed in one park: 35 • Lowest number of anurans observed in one park: 0 • Total number of Lithobates clamitans observed: 37 • Total number of Lithobates catesbiana observed: 67 • Total number of Anaxyrus fowleri observed: 1 • Total number of Lithobates palustris observed: 1
Figure 6. Average number of anurans observed by overall park vegetation type.
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Acronym
Park Name
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ALP
Alley Pond Park
MAS
Massapequa Preserve
HEM
Hempstead Lake State Park
BLY
Blydenburgh County Park
CON
Connetquot River State Park Preserve
VAL
Valley Stream State Park
BEL
Belmont Lake State Park
SHU
Shu Swamp Nature Preserve
CAL
Caleb Smith State Park
TWI
Twin Lakes Preserve
MOR
Morgan Days Park
REV
Reverend Arthur Mackey Park
MIL
Mill Pond Preserve
FOR
Forest City Community Park
GRA
Grant Park
Table 1. Acronyms for site locations.
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Kolozsvary, M. B., & Swihart, R. K. (1999). Habitat fragmentation and the distribution of amphibians: patch and landscape correlates in farmland. Canadian Journal of Zoology, 77(8), 1288-1299. Ray, N., Lehmann, A., & Joly, P. (2002). Modeling spatial distribution of amphibian populations: a GIS approach based on habitat matrix permeability. Biodiversity & Conservation, 11(12), 2143-2165. Nowakowski, A. J., Thompson, M. E., Donnelly, M. A., & Todd, B. D. (2017). Amphibian sensitivity to habitat modification is associated with population trends and species traits. Global Ecology and Biogeography, 26(6), 700-712. Hamer, A. J. (2016). Accessible habitat delineated by a highway predicts landscapescale effects of habitat loss in an amphibian community. Landscape Ecology, 31(10), 2259-2274. Hendricks, J., & Best, D. (2016, May 4). Amphibian Declines in the North Country: The Culprits and the Cures. Retrieved 2020, from https://www.stlawu.edu/sites/default/files/resource/HendricksJakeBestDarcy2016.pdf
Acknowledgements I would like to thank my advisor Dr. Steve M. Raciti of Hofstra University’s Biology Department, as well as the directors of the HUSSRP Program. I would also like to thank my mentor Kristen Greaney , as well as my teacher Heather Hall for helping collect and analyze data.