Quantifying whether different demographic models produce incongruent results on population dynamics of two long-term studied rodent species

1. Population density (ind/ha) of long-term (>15 years) series of CMR populations, using distinct demographic models designed for both open and closed populations, were analysed for two sympatric species of rodents (Myodes glareolus and Apodemus flavicollis) from a mountain area in central Italy, in order to test the relative performance of various employed demographic models. In particular, the hypothesis that enumeration models systematically underestimate the population size of a given population was tested.2. Overall, we compared the performance of 7 distinct demographic models, including both closed and open models, for each study species. Although the two species revealed remarkable intrinsic differences in demography traits (for instance, a lower propensity for being recaptured in Apodemus flavicollis), the Robust Design appeared to be the best fitting model, showing that it is the most suitable model for long-term studies.3. Among the various analysed demographic models, Jolly-Seber returned the lower estimates of population density for both species. Thus, this demographic model could not be suggested for being applied for long-term studies of small mammal populations because it tends to remarkably underestimate the effective population size. Nonetheless, yearly estimates of population density by Jolly-Seber correlated positively with yearly estimates of population density by closed population models, thus showing that interannual trends in population dynamics  were uncovered by both types of demographic models, although with different values in terms of true population size

Population surveys of Nile crocodiles (Crocodylus niloticus) in the Murchison Falls National Park, Victoria Nile, Uganda

1. A 12-month-long survey (April 2013 to March 2014) for Nile crocodiles (Crocodylus niloticus) was conducted along a section of the Victoria Nile/Ramsar site of Murchison Falls National Park, in order to update the historic information on crocodile populations in the area, locating nesting areas, determining seasonality patterns and habitat use, and assess the current abundance and the population size trends since the 1960s. The methods employed included visual encounter surveys, transect counts and opportunistic methods, by using boats.2. In general, there were diurnal and seasonal fluctuations in the number of crocodile sightings. The crocodile sightings peaked between the months of June and August, with the highest mean number of sightings encountered on any single day being 67 (in July 2013), and the second peak was between January and March with  the highest mean of 118 recorded in January 2014. The second peak also coincided with the crocodile breeding  season. This clearly shows that the distribution of the sub-population sampled followed a climatic regime.3. Crocodiles were observed most frequently in water (37%). Grassy banks, islands, river mouths and sandy banks constituted about 47% of the habitats utilised by the crocodile population. Although basking was the most frequent type of activity performed by crocodiles (50%) over the entire survey period, their key activities varied significantly from month to month. Nesting was very visible during the last quarter of the year and the first quarter of the New Year.4. There was a clear decline of the abundance of crocodiles in this population between 1960s and nowadays. This declining trend was obvious also taking into account the various survey methodologies employed over the decades

Le partage des ressources dans les communautés de tortues terrestres : une revue des évidences

In this study I reviewed the studies on the community organization of terrestrial turtles to examine the main patterns of resource partitioning, and to predict whether interspecifi c competition may be or may not be an important organizing force for these ectotherms. These reptiles exhibit four (nearly) constant ecological/life-history traits that may affect the role and the infl uence of interspecifi c competition: (i) low species richness, (ii) high longevity, (iii) herbivorous/omnivorous dietary habits, and (iv) low population density. Based on the expectations derived from these ecological characteristics, I predicted that interspecifi c competition should be of lesser relevance for these turtle communities than for other reptilian communities (lizards, snakes). After reviewing the international literature, I concluded that most of the turtle communities around the world appear currently uninfl uenced by interspecifi c competition. Much of their species diversity refl ects geographic replacement of one species by another. In the regions of the world where two or more species are sympatric, current interspecifi c competition is also of relatively low importance, because the sympatric species tend to partition very clearly the spatial axis or the food axis. By Monte Carlo simulations of niche overlap data versus current niche overlap data at a geographic region in tropical Africa where the community ecology of three sympatric species of terrestrial turtles, three of scincid lizards, four of chameleons, and nineteen of snakes, was accurately studied, I concluded that the interspecifi c competition among turtles was statistically lower than that among these other reptiles, with the spatial niche being the niche dimension most clearly partitioned by turtles in comparison with the other ectotherms. Hence, terrestrial turtles would be unusual among reptiles with respect to the un-infl uence of the competition process for their community ecologydences. - Le présent travail analyse les études de l'organisation des communautés de tortues terrestres afin d'examiner les principaux patterns de partage des ressources et de voir si la compétition interspécifique constitue ou non une force structurante importante pour ces ectothermes. Ces reptiles montrent quatre traits quasi constants dans leur écologie et leur histoire de vie : (i) une faible richesse spécifique, (ii) une forte longévité, (iii) une alimentation de type herbivore/omnivore et (iv) une faible densité de population. Sur la base de ces caractéristiques, on peut prédire que la compétition interspécifique serait moins pertinente pour l'organisation des communautés de tortues que pour celles des autres reptiles (lézards et serpents). L'examen de la littérature internationale amène à conclure que la plupart des communautés de tortues de par le monde ne sont actuellement pas influencées par la compétition interspécifique. Une grande partie de leur diversité spécifique reflète le remplacement géographique d'une espèce par une autre. Dans les régions où deux espèces, ou davantage, sont sympatriques, la compétition interspécifique est relativement faible car ces espèces tendent à se partager très nettement l'espace ou la nourriture. La confrontation de simulations de type Monte Carlo du chevauchement de niche à des chevauchements de niche réels dans une région d'Afrique tropicale où a été bien étudiée la communauté composée de trois espèces de tortues terrestres, trois de lézards scincidés, quatre de caméléons et dix-neuf de serpents, met en évidence que la compétition interspécifique est statistiquement plus faible entre les tortues qu'entre les autres reptiles, la dimension spatiale de la niche étant celle qui sépare le plus clairement les tortues. Les tortues terrestres seraient donc particulières parmi les reptiles pour ce qui concerne la non-influence du processus de compétition dans l'écologie de leurs communautés

Life-history correlates of suboptimal adaptation to rainforest biota by spitting cobras, Naja nigricollis, in southern Nigeria: comparative evidences with sympatric forest cobras, Naja melanoleuca

La zone de forêt continue du sud du Nigéria héberge deux espèces de najas (Naja melanoleuca et N. nigricollis). Elle est actuellement soumise à une forte déforestation due aux activités humaines (extractions et prospections pétrolières notamment, mais aussi effets de la surpopulation). A l'évidence, jusqu'à un passé récent, l'espèce forestière (N. melanoleuca) était beaucoup plus commune que l'espèce savanicole (N. nigricollis) quand les taux de déforestation étaient bien inférieurs aux actuels. De nos jours, l'espèce savanicole est très commune et répandue, non seulement dans les zones péri-urbaines et les habitats altérés, mais aussi en vieille forêt secondaire. De plus, contrairement à l'espèce forestière, elle est particulière en ce qu'elle réduit considérablement son alimentation durant la saison sèche. Cela s'observe chez les adultes et chez les jeunes, chez les mâles et chez les femelles, et dans trois types d'habitats différents (forêt, voisinage des habitations et mosaïque forêt-plantations). Aucun lien avec la biologie de la reproduction ne peut être établi pour expliquer ce fait. L'hypothèse la plus vraisemblable est que cette particularité écologique refléterait une adaptation suboptimale de l'espèce savanicole au biome forestier et serait le « fantôme » d'une récente invasion de la zone forestière par cette espèce savanicole.The region of continuous rainforest in southern Nigeria is inhabited by two species of cobras (Naja melanoleuca and N. nigricollis), and is nowadays subjected to devastating deforestation due to human activity (mainly oil extraction and exploration projects) and overpopulation. Evidence is presented that the forest species (N. melanoleuca) was much more common than the savanna species (N. nigricollis) in the recent past when rates of deforestation were much smaller than today. Nowadays, the savanna species is very common and widespread, not only in suburban and altered habitats, but also in mature secondary forests. Moreover, contrary to the forest species, it is peculiar in that it greatly reduces its feeding rates during the peak of the dry season. These reduced feeding rates were observed in both adults and juveniles, in both males and females, and in three different habitat types (forest, suburbs, and forest-plantation mosaic). No links with reproductive biology can be advocated to explain such a pattern. It is hypothesized that this ecological pattern reftects suboptimal adaptation of the savanna species to rainforest biota, and is a "ghost" of this species' recent invasion of the rainforest region

First assessment of age and sex structures of elephants by using dung size analysis in a West African savannah

1. An age and sex structure study of the West African savannah elephant (Loxodonta africana africana) population of the Nazinga Game ranch (Burkina Faso) was carried out using direct sightings of individuals near water points, where they group during hot periods of the day, and droppings circumference measurements of dung pile along line transects, during the dry seasons of 2007 and 2008. The age structure, from direct observation data, was estimated by classifying the individuals into 9 age-class-categories based on body size and eruption (length) of tusks.2. The frequency distribution of number of individuals into the age-class-categories showed high similarity with the distribution of circumference measurements of dung-piles that the individuals were seen depositing. Fifty dung-piles measured soon after they were deposited (Class A) and after they dried (to class C) showed a significant difference between the circumference measurements in relation to the time elapsed between the measurements.3. The frequency distribution of dung circumference classes of the observed elephants was similar to that of the dung-piles measured along the transects in 2008. Therefore, dung-piles measurements were used to estimate the Nazinga Game Ranch savanna elephant population’s age and sex structures at the end of dry seasons of 2007 and 2008. We advocated that the Nazinga elephant population consisted mainly of sub-adults.4. The sex ratio was estimated to be in favour of females (1/2). The age-class-specific sex ratio was uneven for calves and young individuals, while being in favour of females with adults. Individuals of less than 1 year represented 6% of the population during the study period

Habitat use and food habitats of a gecko population in a west African suburban area

1.The spatial and trophic ecology of Afrotropical gecko populations are poorly known. Here, we report ecological observations on Brook’s House Gecko (Hemidactylus angulatus), a widespread gekkonid species, in the Rivers State University of Science and Technology campus, Port Harcourt, Nigeria.2. A total of 488 gecko individuals were recorded during the present study, in two surveyed habitat types: (i) plantationm trees (PTH) and (ii) buildings (BDH). In PTH, they were observed in 13 out of 15 species of trees present in the study area, with their (log) frequency of sightings being positively correlated to the (log) frequency of surveyed trees per species.3. The geckos used substantially the non-native ornamental trees of the PTH habitat. Pinus ponderosa and Elaeis guineensis were significantly preferred by geckos over all the other tree species.4. Geckos also used frequently the buildings (BDH habitat) at the university campus. There was no correlation between (log) area of each building and (log) number of observed lizards.5. We collected faeces from 51 gecko individuals in dry season and 66 in wet season. There were no significant dietary differences between seasons, with Diptera and adult Lepidoptera dominating in the diet.6. Dietary habits of geckos differed significantly between habitat types, with Araneae and Lepidoptera (larvae) being eaten much more frequently in BDH, and in Coleoptera and Isopoda that were eaten much more frequently in PTH The diversity dietary metrics (Shannon and Dominance indices) were very similar either between seasons or between habitats.7. Our independent set of analyses (diet diversity metrics; contingency tables on taxonomic dietary composition and rank-abundance diagrams) showed that lizards exhibited a same feeding strategy in both wet and dry seasons as well as in the two habitat types, although the diet composition differed significantly between habitats.8. A “mixed” foraging strategy was apparently used by Hemidactylus angulatus at the study area, as also observed in other gekkonid species from elsewhere

Succès reproducteur individuel et taille de ponte dans une population de la couleuvre semi-aquatique Natrix tessellata en Italie centrale : les plus petits mâles et les plus grandes femelles sont-ils avantagés ?

Le succès de la formation des couples et de la reproduction de Natrix tessellata, serpent semi-aquatique, a été étudié dans le centre de l'Italie. Le succès des appariements a été établi en suivant par radiopistage 10 mâles et 12 femelles durant la période d'accouplement et en comptant combien chaque individu avait de partenaires sexuels en fonction de sa taille corporelle (longueur museauanus). Les femelles étaient significativement plus grandes que les mâles. Deux patrons opposés de succès individuel ont été mis en évidence dans la population : un succès d'appariement plus grand pour les plus petits mâles et pour les plus grandes femelles. De fait, chez les mâles, il y avait une relation significative entre la taille du mâle et le nombre de femelles avec lesquelles il s'accouplait tandis que les plus grandes femelles étaient courtisées et s'accouplaient avec un plus grand nombre de mâles. La taille maternelle était positivement liée au nombre d'œufs pondus

How much do the common goods of rural and semi-natural landscape cost? A case study

A Contingent Valuation (CV) was used to estimate the common goods’ overall value of three landscapes (woodlands, wetlands, rural landscape) of the Province of Rome, to use them for policy and administration purpose. Both single and multi-bounded discrete choice models was used. The results are similar between models with a repeated maximum likelihood trend of decreasing mean values from rural landscape to wetlands. The statistical robustness of this trend can be explained by the different organization of multiple consequential and deontological motives that build up preferences. The value assigned by tax payers to common goods analysed sums to a large extent up to the province budget and mean direct use values per hectare are comparable (cropland) or much smaller (woodlands) than indirect and non use values. The indications obtained could be considered robust enough to address decisions and policies (like that of rural development) about how much to pay for common goods management services

Shared ecological knowledge and wetland values: a case study

The estimation of wetlands’ non-use values to build up a total economic evaluation can be based on stated preference methods, which derives from the standard economic model that assumes a rational assessment of the consequence of preferences on personal utility. The paper describes the citizens’ shared ecological knowledge (SEK) of wetlands functions. It descibes SEK nature, SEK relation with the official knowledge, the relation between the motivations outlined by SEK and those expected by the standard economic model. The results demonstrate that economic preferences are driven by multiple motivations well rooted in the SEK’s social nature, and not by simply consequential motivations. In this case study, social knowledge of wetlands' ecological functions is proportionally related to people's living proximity to those wetlands. Unexpectedly, SEK of historically well-known and critically important services like hydraulic and hydrologic services has also been diminishing. Furthermore, there is a partial or clear-cut separation between official knowledge and SEK on crucial aspects like wetlands’ climate change role. This approach helps to construct a motivational framework to derive values that are useful as long as they allow accounting for a complex socio-cultural capital in the public decision making process