Abstract
AbstractRecent ecological theories propose that species reach their highest abundance and genetic diversity in the center of their ecological niche and decline toward the edges. We assessed whether Lyle's flying fox, Pteropus lylei, abundance and genetic diversity were correlated with niche centroid distance using an ecological niche model as a proxy for fundamental niche (NF). Alternatively, we assessed whether P. lylei abundance and genetic diversity were correlated with fine‐scale environmental factors as a proxy of the species’ realized niche (NR). We examined relationships between abundance and environmental factors at coarse and fine scales as proxies of NF and NR, respectively. For coarse scale, ecological niche of P. lylei was modeled using all available occurrence records in Thailand, Cambodia, and Vietnam, coupled with climatic data. We conducted field measurements of P. lylei abundance and used genetic structure data across a large portion of the species’ range. We measured Euclidean distances between abundance and genetic data and the niche centroid in environmental dimensions. Spearman’s correlation was estimated between abundance and genetic diversity vs. distance to the niche centroid. Complementarily, for the fine‐scale test, we measured multiple regression models between abundance and genetic diversity versus the normalized difference vegetation index (NDVI), local temperature, percent area of waterbodies, human density, and number of Buddhist temples. We failed to detect relationships between abundance and genetic diversity with the distance to the niche centroid in the coarse‐scale model. When using the fine‐scale, landscape‐level data, we found negative correlation between genetic diversity and number of temples. The data available were unable to support niche centroid hypothesis for the current distribution and abundances of P. lylei. We note that our failure to find an association does not support nor reject the niche centroid hypothesis. Instead, our capacity to test the niche centroid hypothesis may be limited by our ability to use empirical data to accurately reconstruct NF from field observations only. Future research may require physiology‐based experimental approaches to explore relationships between species abundances and the niche structure.
Highlights
Understanding geographical patterns of species abundances is one of the most important challenges in ecology
The ecological niche model revealed that areas in close to P. lylei niche centroid are mostly in the Thailand, Cambodia, and Vietnam and included area of southern of Lao
When species abundance was assessed based on landscape-level variables as proxies of NR (Fig. 2), we found no correlation between P. lylei abundance and normalized difference vegetation index (NDVI) (q = À0.147), percent area of waterbody (q = À0.252), human density (q = À0.158), or number of temples (q = 0.010; Appendix S1: Fig. S1), annual mean temperature (q = À0.412, P = 0.024; Appendix S1: Fig. S1C) was negatively correlated with P. lylei abundance
Summary
Understanding geographical patterns of species abundances is one of the most important challenges in ecology. Knowledge of the geography of abundances can help elucidate the finescale causes of species range limits, gene flow within populations, and population dynamics. The abundant center hypothesis states that population abundance will peak at the center of a species’ geographic range and decline toward the periphery (Hengeveld and Haeck 1982, Brown 1984). The niche centroid hypothesis proposes a negative association between species’ abundance and the distance to the niche centroid (Borregaard and Rahbek 2010, Martınez-Meyer et al 2013, Manthey et al 2015, Weber et al 2017, Dallas et al 2017). The niche centroid hypothesis proposes that species abundances should be measured in environmental dimensions rather than in geographic space
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