2.4 Niche differentiation comparison
The ecological niche space occupied by a population, which depends on
environmental variables influencing population occurrence, can be
estimated using the n-dimensional ecological
hypervolume
(Lê et al., 2008). Using the R package hypervolume, we then estimated
the four-dimensional hypervolumes for the EIOS and WPI populations based
on the selected principal components. The size of the population’s niche
space can be quantified by the values of hypervolume, a unitless
measure. We used the R package BAT to calculate the niche
differentiation between the EIOS and WPI populations. Total niche
differentiation
(βTotal)
represents the degree of overlap or separation between two hypervolumes.
It can be further divided into two parts: niche contraction/expansion,
which indicates the net variations in how much space each hypervolume
encompasses, and niche shift, which represents the replacement of the
space between the hypervolumes inhabited by two populations (Carvalho &
Cardoso, 2020; Mammola & Cardoso, 2020).