Blowin' in the wind: Dispersal of Glossy Ibis Plegadis falcinellus in the West Mediterranean basin

The movement of organisms is a central process in ecology and evolution, and understanding the selective forces shaping the spatial structure of populations is essential to conservation. Known as a trans-Saharan migrant capable of long-distance flights, the Glossy Ibis Plegadis falcinellus' dispersal remains poorly known. We started a ringing scheme in 2008, the first of its kind in North Africa, and ringed 1121 fledglings over 10 years, of which 265 (23.6%) were resighted. Circular statistics and finite mixture models of natal dispersal indicated: (1) a strong West/Northwest-East/Southeast flight orientation; (2) Glossy Ibis colonies from North Africa and Southern Europe (particularly on the Iberian Peninsula) are closely linked through partial exchanges of juvenile and immature birds; (3) unlike birds from Eastern Europe, North African Glossy Ibis disperse to but do not seem to undergo regular round-trip migration to the Sahel; (4) young adults (>2-years-old) have a higher probability of dispersing further than individuals in their first calendar year (<1-year-old); and (5) dispersal distance is not influenced by sex or morphometric traits. Together, these results enhance our knowledge of the dispersal and metapopulation dynamics of Glossy Ibis, revealing large-scale connectivity between the Iberian Peninsula and Algeria, likely driven by the spatial heterogeneity of the landscape in these two regions and the prevailing winds in the Western Mediterranean.

Sex differences in condition dependence of natal dispersal in a large herbivore: dispersal propensity and distance are decoupled

Evolution should favour plasticity in dispersal decisions in response to spatial heterogeneity in social and environmental contexts. Sex differences in individual optimization of dispersal decisions are poorly documented in mammals, because species where both sexes commonly disperse are rare. To elucidate the sex-specific drivers governing dispersal, we investigated sex differences in condition dependence in the propensity and distance of natal dispersal in one such species, the roe deer, using fine-scale monitoring of 146 GPS-collared juveniles in an intensively monitored population in southwest France. Dispersal propensity increased with body mass in males such that 36% of light individuals dispersed, whereas 62% of heavy individuals did so, but there was no evidence for condition dependence in dispersal propensity among females. By contrast, dispersal distance increased with body mass at a similar rate in both sexes such that heavy dispersers travelled around twice as far as light dispersers. Sex differences in the strength of condition-dependent dispersal may result from different selection pressures acting on the behaviour of males and females. We suggest that females disperse prior to habitat saturation being reached, likely in relation to the risk of inbreeding. By contrast, natal dispersal in males is likely governed by competitive exclusion through male-male competition for breeding opportunities in this strongly territorial mammal. Our study is, to our knowledge, a first demonstration that condition dependence in dispersal propensity and dispersal distance may be decoupled, indicating contrasting selection pressures drive the behavioural decisions of whether or not to leave the natal range, and where to settle.

Rodents' responses to manipulated plant litter and seed densities: implications for restoration

Rodent populations in arid grasslands do not always track seed production, possibly due to high levels of plant litter. When natural disturbances are suppressed, litter accumulates becoming physically complex, causing rodents to harvest fewer seeds per equivalent time foraging. It also alters security from predation. Restoring natural disturbances may be an important element in conserving rodent communities. The aim of this study was to assess the influence of two levels of plant litter cover and seed densities on nocturnal rodent population characteristics in a semiarid grassland. Specifically, I hypothesized that kangaroo rats, pocket mice, grasshopper mice, and total rodents would be higher in the sparse plant litter treatment than dense litter, whereas deer mice would be lower in sparse plots. I further hypothesized that kangaroo rats and deer mice would be higher in the seed augmented treatment compared to the unseeded treatment. A prescribed fire removed litter in four of eight plots prior to sowing native seeds 1 year postfire into two burned and two unburned plots. Rodents were live-trapped during spring and fall 1 year. Sparse litter treatment had higher total rodent abundance, biomass, and frequency of offspring compared to dense plots indicating use of stored seeds. Banner-tailed kangaroo rats had higher abundance, implying reduced predation risk. Pocket mice body mass was greater in dense plots. After winter, seeded plots had higher kangaroo rat body mass and grasshopper mice abundance than unseeded, reflecting the use of stored seeds. These short term results demonstrate litter's physical complexity may be equivalent to seed pulses on the responses of nocturnal rodents. Managers might positively influence grassland rodents by providing a mosaic of varying levels of plant litter.

The physiology of movement

Movement, from foraging to migration, is known to be under the influence of the environment. The translation of environmental cues to individual movement decision making is determined by an individual's internal state and anticipated to balance costs and benefits. General body condition, metabolic and hormonal physiology mechanistically underpin this internal state. These physiological determinants are tightly, and often genetically linked with each other and hence central to a mechanistic understanding of movement. We here synthesise the available evidence of the physiological drivers and signatures of movement and review (1) how physiological state as measured in its most coarse way by body condition correlates with movement decisions during foraging, migration and dispersal, (2) how hormonal changes underlie changes in these movement strategies and (3) how these can be linked to molecular pathways. We reveale that a high body condition facilitates the efficiency of routine foraging, dispersal and migration. Dispersal decision making is, however, in some cases stimulated by a decreased individual condition. Many of the biotic and abiotic stressors that induce movement initiate a physiological cascade in vertebrates through the production of stress hormones. Movement is therefore associated with hormone levels in vertebrates but also insects, often in interaction with factors related to body or social condition. The underlying molecular and physiological mechanisms are currently studied in few model species, and show -in congruence with our insights on the role of body condition- a central role of energy metabolism during glycolysis, and the coupling with timing processes during migration. Molecular insights into the physiological basis of movement remain, however, highly refractory. We finalise this review with a critical reflection on the importance of these physiological feedbacks for a better mechanistic understanding of movement and its effects on ecological dynamics at all levels of biological organization.

Generalist dispersal and gene flow of an endangered keystone specialist (Dipodomys ingens)

Movement ecology and dispersal capabilities inherently drive genetic structure across landscapes. Through understanding dispersal and gene flow of giant kangaroo rats (Dipodomys ingens), conservation efforts can be focused, and we can further understand how genetic structure persists in this highly endemic small mammal. Here, we genetically identify parent–offspring and sibship relationships among 239 giant kangaroo rats using 15 microsatellites in the northern part of the species range and describe the individual genetic-spatial variation using a Moran eigenvector map (MEM). We further employ two landscape genetic analyses (isolation by resistance [IBR] and least cost paths [LCPs]) and two individual-based genetic metrics (Dps and a codominant marker distance from GenAlEx) to determine landscape factors (precipitation, slope, vegetation community, and roads) that influence gene flow. We found 19 pairs of related individuals, of which 18 were less than 250 m apart, but one sibling pair was 5.52 km apart, suggesting greater dispersal capabilities than previously noted. We found hierarchal spatial genetic structure using a MEM, with 3–4 genetically similar regions and two genetically similar subregions. Finally, we found low correlative strength between landscape features and gene flow. IBR consistently outperformed LCPs, and there was evidence that regions with 250–350 mm of precipitation and slope ≤ 5° promoted connectivity. We recommend that managers focus on habitat protection rather than corridor maintenance, with the caveat that anthropogenic factors were minimally considered in this study.

Individual dispersal decisions affect fitness via maternal rank effects in male rhesus macaques

Natal dispersal may have considerable social, ecological and evolutionary consequences. While species-specific dispersal strategies have received much attention, individual variation in dispersal decisions and its fitness consequences remain poorly understood. We investigated causes and consequences of natal dispersal age in rhesus macaques (Macaca mulatta), a species with male dispersal. Using long-term demographic and genetic data from a semi-free ranging population on Cayo Santiago, Puerto Rico, we analysed how the social environment such as maternal family, group and population characteristics affected the age at which males leave their natal group. While natal dispersal age was unrelated to most measures of group or population structure, our study confirmed earlier findings that sons of high-ranking mothers dispersed later than sons of low-ranking ones. Natal dispersal age did not affect males’ subsequent survival, but males dispersing later were more likely to reproduce. Late dispersers were likely to start reproducing while still residing in their natal group, frequently produced extra-group offspring before natal dispersal and subsequently dispersed to the group in which they had fathered offspring more likely than expected. Hence, the timing of natal dispersal was affected by maternal rank and influenced male reproduction, which, in turn affected which group males dispersed to.

Sexual dimorphism and condition dependence in the anal pad of the small Indian mongoose (Herpestes auropunctatus)

Secondary sexual traits tend to be sexually dimorphic, and theory predicts that such traits should also be condition-dependent in a sex-specific manner. We investigate these phenomena in a field study of the small Indian mongoose (Herpestes auropunctatus (Hodgson, 1836); formerly Herpestes javanicus (É. Geoffroy Saint-Hillaire, 1818)), in the first attempt at understanding secondary sexual traits and sexual selection in this species. Small Indian mongooses are solitary and nonterritorial, and they likely depend on chemical (scent) rather than visual or acoustic signals for communication. Additionally, they possess a fleshy projection around their anus, the anal pad, thought to aid in scent-marking. Our results revealed strong male-biased sexual dimorphism in mass, skull and body lengths, canine diameters, and anal pad area. After controlling for the influence of body length, males were 31% heavier and possessed anal pads that were 68% larger than females’. Additionally, anal pad size was positively related to body size in males but not in females and was condition-dependent in males but not in females. Taken together, our findings provide indirect evidence that the anal pad might have evolved, at least in part, via sexual selection.