Which Factors Determine Spatial Segregation in the South American Opossums (Didelphis aurita and D. albiventris)? An Ecological Niche Modelling and Geometric Morphometrics Approach

Abstract

Didelphis albiventris and D. aurita are Neotropical marsupials that share a unique evolutionary history and both are largely distributed throughout South America, being primarily allopatric throughout their ranges. In the Araucaria moist forest of Southern Brazil these species are sympatric and they might potentially compete having similar ecology. For this reason, they are ideal biological models to address questions about ecological character displacement and how closely related species might share their geographic space. Little is known about how two morphologically similar species of marsupials may affect each other through competition, if by competitive exclusion and competitive release. We combined ecological niche modeling and geometric morphometrics to explore the possible effects of competition on their distributional ranges and skull morphology. Ecological niche modeling was used to predict their potential distribution and this method enabled us to identify a case of biotic exclusion where the habit generalist D. albiventris is excluded by the presence of the specialist D. aurita. The morphometric analyses show that a degree of shape discrimination occurs between the species, strengthened by allometric differences, which possibly allowed them to occupy marginally different feeding niches supplemented by behavioral shift in contact areas. Overlap in skull morphology is shown between sympatric and allopatric specimens and a significant, but weak, shift in shape occurs only in D. aurita in sympatric areas. This could be a residual evidence of a higher past competition between both species, when contact zones were possibly larger than today. Therefore, the specialist D. aurita acts a biotic barrier to D. albiventris when niche diversity is not available for coexistence. On the other hand, when there is niche diversification (e.g. habitat mosaic), both species are capable to coexist with a minimal competitive effect on the morphology of D. aurita.

Mandible size and shape in extant Ursidae (Carnivora, Mammalia): A tool for taxonomy and ecogeography

“…To better characterize mandibular shape variation within our sample, a variation partitioning approach was also applied using shape variables as response and climate (continuous standardized variables inclusive of all the 19 bioclim), taxonomy (categorical variable), sex, and size (continuous variable, ln CS) as explanatory variables (Cáceres et al., ; Cardini et al., ; Meloro et al., ,b). Variation partitioning allows testing for contribution of climate, size, sex, and taxonomic categorization on mandibular shape variance, taking their interaction into account.…”

“…To take also the impact of sexual dimorphism into account, we used for this analysis a subsample of 66 specimens for which geographic location was available. In this case, specimens were not averaged by geographic location to maximize sample size and include intraspecific sexual variation (Cáceres et al., ). This analysis was performed using the R package vegan (Oksanen et al., ).…”

Didelphis albiventris: an overview of an unprecedented transcriptome sequencing of the white-eared opossum

“…These marsupials are widely distributed in South America (including Cerrado, Caatinga and Pantanal areas) [38][39][40][41][42], and they have been used as model organisms to understand human infections such as Chagas disease [43,44] and leishmaniasis [45]. Cáceres [46] suggested that D. albiventris is an important agent as a seed spreader.…”

Can Niche Modeling and Geometric Morphometrics Document Competitive Exclusion in a Pair of Subterranean Rodents (Genus Ctenomys) with Tiny Parapatric Distributions?

“…In addition, we used natural history information for the species, including spatial distribution 23 – 27 , diet composition 28 , and microhabitats requirements 29 , 30 . The combination of both techniques 31 , together with natural history information, can provide stronger, and likely complementary evidence of competitive interactions than the use of any of them alone.…”