Relationship between plot and species range geometry impacts species richness and extinction
The question of how to best allocate a limited amount of land for maximum conservation impact has long been debated in ecology. We investigate the relationship between reserve/sample plot geometry and species range geometry to find how that relationship affects species richness, endemic richness, and edge-to-area ratios. We simulated various species range geometries and then took measures of the above traits under varying sample plot geometries. We then looked at how these measures are affected by different plot geometries overlayed on empirical species distributions.
We find an increase in endemic richness as a plot’s shape tends towards the expected shape (and orientation) of species’ ranges, e.g. a square plot has more endemics than a rectangular plot when species are expected to have a square range. Thus just by analyzing the geometry of potential removed plots, we can minimize extinction, or species endemic to the removed plot, when destroying habitat. We similarly nuance the often observed phenomenon that more elongated plots have higher species richness than square plots of the same area by showing that species richness actually increases with increasing dissimilarity between plot and expected species range shape and orientation. With endemic and species richness trends opposing each other with respect to geometry, we infer a tradeoff between the number of species captured and average population size with plot elongation. An ideal reserve would then be elongated to the extent that populations remain above their critical population size. Though the topology of the remaining habitat does not directly affect the number of endemics lost, it determines the amount of edge habitat created, which in turn has conservation implications. Considering geometry and topology in reserve design can help us maximize the number and persistence of species captured by a reserve and minimize extinction and edge habitat creation when habitat must be removed.