The ambient energy hypothesis and the habitat heterogeneity
hypothesis
The
ambient
energy hypothesis predicts that areas with high productivity can
accommodate more species, and species interaction will be more frequent
in the areas with high species richness, which could promote species
specialization and lead to finer niche separation and smaller range size
(Hildrew, Townsend, & Francis, 1984; Currie, 1991). However, to our
knowledge, no empirical study found evidence to support the ambient
energy hypothesis, whether along the latitude gradient or the
elevational gradient. On the contrary, studies have shown positive or
irrelevant relationships between primary productivity and species mean
range size (e.g., Luo et al., 2011; J.-Y. Kim et al., 2019). In our
case, we also detected a positive relationship between species mean
range size and primary productivity.
Habitat heterogeneity also plays an important role in determining the
species distribution (Whitton, Purvis, Orme, & Olallatarraga, 2012).
Different combinations of habitat types can affect the energy allocation
of an ecosystem. For example, higher habitat heterogeneity can promote
the subdivision of limited resources (Kerr & Packer 1997). Therefore,
the habitat heterogeneity hypothesis was proposed as a supplement to the
ambient energy hypothesis (J.-Y. Kim et al., 2019). The habitat
heterogeneity hypothesis indicates that complex habitats should
facilitate the resource allocation in ecosystems, which could lead to
greater species specialization and coexistence. Under certain
conditions, an increase in available space and shelters, as well as
opportunities for isolation and divergent adaptation, is thought to
enhance species coexistence, persistence, and diversification (Rohde
1992). However, our results found little evidence to support the habitat
heterogeneity hypothesis, and the area with higher
habitat heterogeneity does not
necessarily mean a larger area of suitable habitat. Our result showed
that habitat heterogeneity was the lowest while the area percentage of
suitable habitat types was the highest (Figure S3 in Appendix 2). The
relationship between species mean range size and habitat heterogeneity
in Lebu Valley may be weak in this case.