Ricardo A. Ojeda

Rodentia has a high species number and chromosomal variability. The South American genus Akodon is one of the most speciose muroids, with more than 40 species included in several species groups. Here, we characterize cytogenetically specimens of Akodon from central-western Argentina. Subsequently, we reviewed and analyzed the cytogenetic data for this genus, build a phylogeny and mapped chromosome changes to interpret its evolution. Specimens of A. dolores from central-western Argentina have 2n=42-44/FNa=44 (46, 48) due to a Robertsonian rearrangement. Our data expand the distribution range known for this polymorphism and confirm its geographic structure. Other specimens had 2n=40/FNa=40, representing populations of A. oenos, A. polopi, and A. spegazzinii. All karyotypes have a low amount of heterochromatin, concentrated in centromeres and sex chromosomes, as in other rodents. The complement with 2n=40/FNa=40 is the most frequent in Akodon and is shared by most species in some groups. Chromosome numbers are very diverse. The FNa shows less variability; FNa=42 was recovered as ancestral, excluding A. mimus, which was connected at the base of the Akodon tree and has FNa=44. This indicates a complex chromosome evolution in Akodon, and suggests that reductions and increases in the 2n and FNa evolved independently in some lineages.

Abrocoma schistacea Thomas, 1921 is an abrocomid rodent commonly known as the Sierra del Tontal chinchilla rat. This medium-sized chinchilla rat is a rock specialist that inhabits the pre-Andean foothills of southern San Juan Province (Argentina) within an elevation range of 1,100–2,900 m. Its saxicolous specializations include padded feet with leathery tubercles on the pads. Incisors are large and orthodont; molariform teeth appear broad. A. schistacea is a creosotebush dietary specialist that can be distinguished from other chinchilla rats by living in groups of 3–4 individuals. This species is categorized as of low conservation concern in Argentina but is currently listed as “Data Deficient” by the International Union for Conservation of Nature and Natural Resources.

The Gran Chaco in central South America is a major savanna woodland ecosystem. Accelerated changes in land use within it have resulted in a complex matrix of areas with varying capabilities for sustaining wildlife. Furthermore, hunting and habitat loss increasingly threaten the functional diversity of mammals found there. We assess the potential consequences of the loss of large and medium‐sized native mammalian herbivores and frugivores on Chacoan ecosystem functioning, focusing on their role and conservation status in the Argentine Chaco. Our review shows that almost 50% of the largest frugivorous mammals present in the Argentine Chaco are threatened and exhibit declining population trends. Their decline may cause changes in vegetation composition, since almost 53% of the Chacoan woody plant species display endozoochory as their seed dispersal mechanism. Moreover, 80% of the largest herbivores are threatened, which may also lead to a compositional change in savanna vegetation. There is a significant void of information regarding the population status of native mammals in the Argentine Chaco and the functional roles they play in the ecosystem, and there are few studies examining the consequences of their potential loss. We express our concern with the major changes taking place in this subtropical region due to significant and rapid habitat transformations and emphasize the important role of ecological functionality in restoration and conservation planning in the Gran Chaco.

Although scaling biodiversity is a common topic in ecology, scaling functional biodiversity is a major theoretical and analytical challenge, mainly because trait differentiation and regulating processes occur at different spatial scales. Here, we propose a method to scale functional biodiversity by comparing the relative dominance of convergent versus divergent functional traits across environmental gradients. Particularly, in highly variable systems such as deserts, one would expect species convergence in the use of an abundant resource through niche filtering, promoting functional redundancy (stability hypothesis), but at which spatial scale? We tested this approach using small mammal assemblages of the Monte Desert (Argentina, South America) and found that divergent traits are dominant on smaller spatial scales, whereas convergent traits are present only at the highest spatial scale. Functional complementarity was recorded at the community and meta‐community levels, suggesting that niche partitioning is the main regulating process and diet the major divergent trait. At regional scale, divergent traits were also present, indicating that biodiversity is also regulated by niche filtering. Finally, we found that the stability hypothesis cannot be generalized for desert systems but depends on the spatial scale. This novel approach offers new insights into the search for an integrative perspective on functional biodiversity.

Biodiversity patterns are the result of the interaction of numerous contemporary factors and historical opportunities for allopatric speciation. Seve