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J.O. López-Martínez et al. 2010. Ecological factors influencing beta diversity at two spatial scales in a tropical dry forest
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Table 2. Variation partitioning of woody plant species composition at the landscape scale.
4. Discussion
MARGINAL PERCENT
PREDICTOR
VARIABLE VARIATION VARIATION
EXPLAINED EXPLAINED
Landscape structure 0.17 16.5
Space 0.14 13.8
Shared 0.01 1.4
Total inertia explained 0.32 31.7
Unknown 0.68 68.3
Total Inertia 1.00
The amount of variation in species composition (beta diversity) was higher at the
landscape scale (32%), than at the local scale (13.89%). This indicates that differences in
species composition are greater among landscape units with varying degrees of fragmentation,
compared to differences among vegetation cover classes (Figures 2a, 3a).
Arroyo-Mora et al. (2005) also found differences in species composition among
successional classes in neotropical dry forests.
At both spatial scales, environmental factors and spatial dependence explained a similar
amount of variation in species composition (Tables 1. 2). This lends support to both niche
theory (environmental drivers, Grubb, 1977) and the neutral theory (based on dispersal
limitation, Hubbell 2001, Chust et al. 2006). This is consistent with the recently proposed
continuum hypothesis of Gravel et al. (2006), which states that both niche theory and dispersal
limitation play an important role in beta diversity.
Variation partition at the local scale showed that soil attributes had a higher contribution
to explaining beta diversity than stand age or landscape structure (Table 1). In particular, soil
organic matter and pH were the variables most strongly associated with change in species
composition (Figure 2b). At the landscape scale, landscape structure was the most important
contributor to beta diversity (Table 2). The large patch index (LPI), which was the variable most
strongly associated with beta diversity, was also positively associated with the least disturbed
landscape units (Figure 3b). These results concur with other studies indicating that species
composition is affected by several factors and process operating at different spatial scales
(Leibold, 2006, Hubbell, 2001, Parker, 2004).
Although there were fewer environmental and space variables explaining species
composition at the landscape scale than at the local scale, the variation explained by these
variables was more than double at the landscape scale compared to the local scale (31.7% versus
13.8%). This may suggest that disturbance has a greater influence on woody species
composition than vegetation cover.
References
Arroyo-Mora J.P., Sánchez-Azofeifa G.A., Kalácska M., Rivard B. and Janzen D.H. 2005.
Secondary forest detection in a Neotropical dry forest using Landsat 7 ETM+ imagery.
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Borcard, D. and Legendre, P., 2002. All-scale spatial analysis of ecological data by means of
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Borcard, D., Legendre, P. Drapeau, P., 1992. Partialling out the Spatial Component of
Ecological Variation. Ecology, 73(3): 1045-1055.
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.