Kithsiri B. Ranawana

Random walk analysis of ranging patterns of sympatric langurs in a complex resource landscape.

The identification of random walk models to characterize the movement patterns of social groups of primates, and the behavioral processes that give rise to such movement patterns, remain open questions in movement ecology. Movement patterns characterized by a power‐law tail with exponent between 1 and 3 (Lévy flight) occur when animals forage on scarce, randomly distributed resources. For primates and similar foragers with memory processes, movements resembling Lévy flights emerge when feeding trees (targets) are randomly distributed and the trunk size distribution of targets follows a power‐law. We tested three competing random walk models to describe movement patterns of two langur species. We found a truncated power law to be the most suitable model. The power‐law model was poorly supported by the data and hence we found no support for Lévy‐flight‐like behavior. Moreover, the spatial distribution of feeding trees and the probability distribution of feeding tree size differed from values suggested to result in Lévy‐flight‐like patterns. We identify intraspecific territoriality, foraging behavior, and the spatial and size distribution of food patches as plausible mechanisms that may have given rise to the observed movement patterns Am. J. Primatol. 75:1209–1219, 2013.

Does spatial variation in predation pressure modulate selection for aposematism

Abstract It is widely believed that aposematic signals should be conspicuous, but in nature, they vary from highly conspicuous to near cryptic. Current theory, including the honest signal or trade‐off hypotheses of the toxicity–conspicuousness relationship, cannot explain why adequately toxic species vary substantially in their conspicuousness. Through a study of similarly toxic Danainae (Nymphalidae) butterflies and their mimics that vary remarkably in their conspicuousness, we show that the benefits of conspicuousness vary along a gradient of predation pressure. Highly conspicuous butterflies experienced lower avian attack rates when background predation pressure was low, but attack rates increased rapidly as background predation pressure increased. Conversely, the least conspicuous butterflies experienced higher attack rates at low predation pressures, but at high predation pressures, they appeared to benefit from crypsis. Attack rates of intermediately conspicuous butterflies remained moderate and constant along the predation pressure gradient. Mimics had a similar pattern but higher attack rates than their models and mimics tended to imitate the signal of less attacked model species along the predation pressure gradient. Predation pressure modulated signal fitness provides a possible mechanism for the maintenance of variation in conspicuousness of aposematic signals, as well as the initial survival of conspicuous signals in cryptic populations in the process of aposematic signal evolution, and an alternative explanation for the evolutionary gain and loss of mimicry.

Two new localities of the endangered fish Systomus martenstyni (Kottelat & Pethiyagoda, 1991) (Teleostei: Cyprinidae) found in Sri Lanka

Systomus martenstyni is an endemic and endangered fish of Sri Lanka. This species was earlier known to be restricted to the Amban Ganga River basin. Recently two populations of S. martenstyni were located in two major tributaries of River Mahaweli: Loggal Oya and Badulu Oya in the Uva province of Sri Lanka. These new populations are relatively small and are facing the threat of habitat quality degradation and habitat loss. Effective conservation actions should be undertaken to conserve this endangered fish species.