A critical assessment of two species distribution models: a case study of the vervet monkey (Cercopithecus aethiops)

Aim Species distribution models are invaluable tools in biogeographical, ecological and applied biological research, but specific concerns have been raised in relation to different modelling techniques in terms of their validity. Here we compare two fundamentally different approaches to species distribution modelling, one based on simple occurrence data where the lack of an ecological framework has been criticized, and the other firmly based in socio‐ecological theory but requiring highly detailed behavioural information that is often limited in availability. Location (Sub‐Saharan) Africa. Methods We used two distinct techniques to predict the realized distribution of a model species, the vervet monkey (Cercopithecus aethiops Linnaeus, 1758). A maximum entropy model was produced taking 13 environmental variables and presence‐only data from 174 sites throughout Africa as input, with an additional 58 sites retained to test the model. A time‐budget model considering the same environmental variables was constructed from detailed behavioural data on 20 groups representing 14 populations, with presence‐only data from the remaining 218 sites reserved to test model predictions on vervet monkey occurrence. Both models were further validated against a reference species distribution map as drawn up by the African Mammals Databank. Results Both models performed well, with the time budget and maximum entropy algorithms correctly predicting vervet monkey presence at 78.4% and 91.4% of their respective test sites. Similarly, the time‐budget model correctly predicted presence and absence at 87.4% of map pixels against the reference distribution map, and the maximum entropy model achieved a success rate of 81.8%. Finally, there was a high level of agreement (81.6%) between the presence–absence maps produced by the two models, and the environmental variables identified as most strongly driving vervet monkey distribution were the same in both models. Main conclusions The time‐budget and maximum entropy models produced accurate and remarkably similar species distribution maps, despite fundamental differences in their conceptual and methodological approaches. Such strong convergence not only provides support for the credibility of current results, but also relieves concerns about the validity of the two modelling approaches.     

The phylogenetic distribution,anatomy and histology of the post‐cloacal bones and adnexa of geckos

Post‐cloacal bones of gekkotans may be present as a single (medial) pair, two pairs (medial and lateral), or may be lacking. We, herein, demonstrate that the presence of a single medial pair is the ancestral condition for the Gekkota, that the lateral pair is of sporadic occurrence within and between families, except for the Eublepharidae where it is universal, and that absence is also of sporadic occurrence except for the Sphaerodactylidae where it is the ancestral condition. Adult male Tokay geckos (Gekko gecko) possess only the medial pair of bones, and these exhibit a regionally‐specific expression of woven, fibrolamellar, and lamellar bone, and an enclosed medullary cavity. Females and small juvenile males lack bony elements but exhibit a conspicuous band of dense connective tissue located about the anterior and lateral margins of the cloacal sacs. As males grow and attain sexual maturity, the medial post‐cloacal bones condense in this band of dense connective tissue, and are thus shown to be dermal ossifications, similar to osteoderms but with muscular associations (although this is also known for crocodylians). Based upon ontogenetic data we set forth a scenario to explain the loss of the medial post‐cloacal bones in various lineages. Differential staining of the cloacal sacs failed to reveal any specialized glandular structures. Investigation of the post‐cloacal spurs shows them to be associated with cellular connective tissue of a type similar to that found in the vicinity of the medial post‐cloacal bones. This suggests that the lateral post‐cloacal bones may also be dermal bones, but histological evidence is needed to corroborate this. J. Morphol. 277:264–277, 2016. © 2015 Wiley Periodicals, Inc.     

Dissociating Two Stages of Preparation in the Stop Signal Task Using fMRI

Often we must balance being prepared to act quickly with being prepared to suddenly stop. The stop signal task (SST) is widely used to study inhibitory control, and provides a measure of the speed of the stop process that is robust to changes in subjects’ response strategy. Previous studies have shown that preparation affects inhibition. We used fMRI to separate activity that occurs after a brief (500 ms) warning stimulus (warning-phase) from activity that occurs during responses that follow (response-phase). Both of these phases could contribute to the preparedness to stop because they both precede stop signals. Warning stimuli activated posterior networks that signal the need for top-down control, whereas response phases engaged prefrontal and subcortical networks that implement top-down control. Regression analyses revealed that both of these phases affect inhibitory control in different ways. Warning-phase activity in the cerebellum and posterior cingulate predicted stop latency and accuracy, respectively. By contrast, response-phase activity in fronto-temporal areas and left striatum predicted go speed and stop accuracy, in pre-supplementary motor area affected stop accuracy, and in right striatum predicted stop latency and accuracy. The ability to separate hidden contributions to inhibitory control during warning-phases from those during response-phases can aid in the study of models of preparation and inhibitory control, and of disorders marked by poor top-down control.