Resource partitioning in freshwater turtle communities: A null model meta-analysis of available data

Trophic Resource Use by Sympatric vs. Allopatric Pelomedusid Turtles in West African Forest Waterbodies

Organisms that are similar in size, morphological characteristics, and adaptations, including vertebrates, often coexist by partitioning the available resources (food, space, and time). So, studies of the dynamics of these cases of coexistence are scientifically interesting. Here, we study a coexistence case of two species of freshwater turtles inhabiting the forest waterbodies of West Africa, focusing on the dietary habits of the two species. We found that both turtle species are omnivorous generalists, eating both vegetal and animal matter abundantly. However, there were clear interspecific differences, with the larger of the two species (P. cupulatta) eating more vertebrates (mainly fish but occasionally other vertebrates), whereas P. castaneus consumed more invertebrates. These patterns appeared consistently within the species and across sites, highlighting that the same patterns were likely in other conspecific populations from the Upper Guinean forest streams (Côte d'Ivoire and Liberia). Our study also showed that interspecific competition for food does not occur between these two species; instead, previous studies uncovered that a clear partitioning of the habitat niche occurs. We conclude that the food resource is likely unlimited in the study areas, as it is not the case in more arid environments (since food shortages may occur during the dry season). We anticipate that, within the Pelomedusidae communities throughout Africa, intense competition for food probably occurs in the Sahel and Sudanian vegetation zones, particularly during the dry months, but is unlikely within the Guinea and wet savannah region and even less likely in the Guineo-Congolian rainforest region.

Factors contributing to the range expansion and population increase of a native generalist species

Ecological communities are becoming more typified by generalist species in conjunction with anthropogenic activities. Using a long-term dataset (1968-2019), we documented the expansion of a native generalist species, the red-eared slider (Trachemys scripta elegans), into a river community, and studied the subsequent population changes that occurred in conjunction with short- and long-term changes within the ecosystem. Trachemys scripta elegans was able to expand into a new geographic area following a harvesting-induced population decline of a native competitor, the northern map turtle (Graptemys geographica). The population of T. s. elegans remained small for approximately 2.5 decades, then significantly increased in conjunction with habitat degradation in the form of increased silt/sediment deposits and nuisance aquatic vegetation growth. Our results demonstrate how a generalist species can expand and establish a population in an area impacted by multiple anthropogenic stressors. This research reveals how ecological communities become characterized by more generalist species following anthropogenically-induced competitive release caused by harvesting of native competitors, habitat degradation, and extreme flooding associated with land cover and climate change.

Predicting the structure of turtle assemblages along a megatransect in West Africa

Understanding large- and small-scale patterns and the determinants of species richness is central for the study of evolutionary mechanisms. The extent to which species richness in local communities is related to larger-scale processes is a pre-eminent topic in ecological and evolutionary research. To investigate how local and regional species richness are related, we sampled freshwater turtle assemblages in seven localities to represent the variation in ecological conditions along a 90 km south–north megatransect in Benin, West Africa. In each locality, all turtles captured were identified and measured, and the microhabitat in which individual turtles were observed was classified. Based on these data, we used community diversity metrics to compare turtle assemblages. Spatial autocorrelation did not affect our data. For all localities pooled, two species (Pelusios castaneus and Pelomedusa olivacea) were the most common and one species (Trionyx triunguis) was the rarest. Analyses of the commonest and more numerous species showed that the abundance of Pelusios castaneus declined with an increase in latitude and longitude, but the opposite was true for Pelomedusa olivacea. We showed that various characteristics of the microhabitat were significantly correlated with the abundance of the two common species. We found significant but variable south–north gradients in microhabitat use for different turtle species. Our results highlight the importance of studying interactions between local environments, the ecological requirements of each species and their synecological relationships.

Basking activity pattern of the European pond turtle, Emys orbicularis (Linnaeus, 1758) in Babat valley (Gödöllő, Hungary)

The populations of the widespread European pond turtle and their numbers are decreasing in Hungary and other European countries. Knowledge of basking habits, along with other biological characteristics of the species, could be important to preserve the European pond turtle. The purpose of our research was to assess the seasonal and daily basking activity of the European pond turtle, and the effects of weather parameters on sun-basking, for which no prior data exist for Hungary. Our study was carried out in the area of a dammed valley pond system at Gödöllő (Hungary) over two years. The results showed that the seasonal peak of the turtles’ basking (the highest number of observed sun-basking turtles) was in the spring. When using a finer time scale (1.5-hour intervals), we found that daily activity peaks were earlier in the spring and summer (11:00–12:30 h) than in autumn (12:30–14:00 h). Based on three measured temperatures (air temperature in shade and sunlight, water temperature), the number of basking turtles positively correlated with temperatures and varied seasonally; the optimal temperature ranges also shifted during the year. In the spring and autumn, turtles started sun-basking at lower temperatures than in the summer. We observed the narrowest optimal temperature ranges in the summer as well. Based on a Principal Component Analysis of weather parameters, low humidity and high air temperature created optimal basking conditions, whereas high humidity, and low air and water temperatures had an adverse effect.

Do diets vary over large spatial or temporal ranges? A test using interannual and interpopulation data on Diamondback Terrapin (Malaclemys terrapin) diets

Animal diets may vary spatially or temporally as resource availability vary. Diets of species with extensive geographic ranges often span multiple habitats, thus their diets may vary accordingly. Temporal diet variation is rarely explored because most diet studies are short term; this is problematic for long-lived species where individuals may persist as prey availability changes. We analyzed diet variation in Diamondback Terrapins (Malaclemys terrapin (Schoepf, 1793)), which inhabits nearly 70 000 km of United States Atlantic coastline, spanning 16.5°N latitude and 27.4°W longitude and four Köppen climatic zones, and Bermuda. We explored spatially or temporally Diamondback Terrapin diet variation, including populations from Atlantic salt marshes, an Everglades mangrove swamp, the Texas Gulf Coast, and a Caribbean golf course pond. We found remarkably high levels of similarity, indicating that although diets vary according to local prey availability, they are broadly similar at lower taxonomic resolution. Even short-term studies may be sufficient to accurately characterize diets of Diamondback Terrapins. These results are surprising given the geographic range sampled in this study and indicate that Diamondback Terrapin diets are conservative, reflecting local prey availability. Such diets apparently allow Diamondback Terrapins to exploit their extensive range and may allow Diamondback terrapin populations to persist as local prey species wax and wane.

Meta-análisis de la historia del estudio de las tortugas continentales de Colombia

Analizamos las referencias incluidas en una reciente revisión literaria sobre el estado de conocimiento de las tortugas continentales de Colombia. La tasa de publicaciones sobre estas especies ha incrementado exponencialmente desde los años 1950s, aunque muchas de éstas no podrían haber sido detectadas usando búsquedas de literatura por internet. Los tópicos más comunes de las publicaciones fueron sistemática y filo-geografía, ecología de anidación, y manejo. En los años 1970s y 1980s, la tasa de publicaciones sobre temas de ecología y genética de poblaciones ocupando el territorio colombiano, estuvo por debajo de publicaciones sobre estos dos tópicos con poblaciones de las mismas especies en otras regiones de Suramérica. Sin embargo, actualmente la producción en ambas regiones es comparable. En otros países, detectamos una tendencia temporal significativa de publicar cada vez más en inglés y en revistas de mayor impacto; esta tendencia no fue significativa para las publicaciones sobre poblaciones de tortugas colombianas. En Colombia, un número desproporcionado de las publicaciones son sobre especies de tamaños grandes que enfrentan problemas de conservación. Argumentamos que estudios futuros de las especies de tortugas continentales de Colombia relativamente bien conocidas, se deberían enfocar en evaluar la efectividad de los programas de manejo, y también debemos dar prioridad a investigaciones que aumenten el estado de conocimiento de las especies de tortugas continentales poco estudiadas en el país, especialmente de aquellas que actualmente están categorizadas por la UICN como con datos deficientes (DD).

Attributes of basking sites of the European pond turtle (Emys orbicularis) in central Italy

Attributes of basking sites are important elements to study in management plans of threatened freshwater turtles. Here, we analyzed the basking-site characteristics of European pond turtle (Emys orbicularis) populations in a Mediterranean territory of central Italy (Tolfa Mountains, Latium). We used logistic regression and Principal Components Analysis to characterize 29 presence sites versus 61 random sites, through 16 descriptive variables recorded within a 5 m radius from the sighting/target spot. Our analyses revealed that some variables (i.e. water turbidity, presence of small coves, submerged vegetation, and emergent tree-trunks) were those that influenced most strongly the presence of turtles on potential basking sites. Maintenance of deadwood in water and preservation of submerged aquatic vegetation should be included in the management planning for this turtle species in central Italy.

Spatial variation in the littoral vertebrate community of a reservoir relative to physical and biological gradients

Reservoirs possess gradients in conditions and resources along their long (deep-shallow) axis, but the response of littoral vertebrates (fish and turtles) to these gradients is poorly understood. We have quantified the littoral vertebrate communities throughout a small reservoir in Southeastern Ohio during July and August using traps, and related community composition to environmental variables using NMDS ordination. Ordination revealed that fish and turtles were broadly separated in ordination space, and three distinctly different environmental gradients were significantly associated with the underlying observed species abundances. Observed turtle abundance was explained by measurements of bathymetry, turbidity, and benthic resources, but none of these environmental variables were a reliable predictor of observed fish abundance. Temperature was a poor predictor of observed abundance for both fish and turtles independently, but when fish and turtles were considered together, it became apparent that there were cold areas of the reservoir where observed fish and turtle abundances were different than in other areas of the reservoir. These results suggest that the predictor (environmental) variables we used were appropriate for investigating turtle ecology in reservoirs, but that observed fish abundance is mediated by factors that were not modeled. The efficacy of using traps, the ecological implications of considering fish and turtles together as sympatric and potentially competing species, and directions for future study are discussed.

Species richness and evidence of random patterns in assemblages of South American Titanosauria during the Late Cretaceous (Campanian-Maastrichtian)

The Titanosauria were much diversified during the Late Cretaceous, but paleobiological information concerning these sauropods continues to be scarce and no studies have been conducted utilizing modern methods of community analysis to infer possible structural patterns of extinct assemblages. The present study sought to estimate species richness and to investigate the existence of structures in assemblages of the South American Titanosauria during the Late Cretaceous. Estimates of species richness were made utilizing a nonparametric estimator and null models of species co-occurrences and overlapping body sizes were applied to determine the occurrence of structuring in this assemblages. The high estimate of species richness (n = 57) may have been influenced by ecological processes associated with extinction events of sauropod groups and with the structures of the habitats that provided abundant support to the maintenance of large numbers of species. The pseudocommunity analysis did not differ from that expected by chance, indicating the lack of structure in these assemblages. It is possible that these processes originated from phylogenetic inertia, associated with the occurrence of stabilized selection. Additionally, stochastic extinction events and historical factors may also have influenced the formation of the titanosaurian assemblages, in detriment to ecological factors during the Late Cretaceous. However, diagenetic and biostratinomic processes, influenced by the nature of the sedimentary paleoenvironment, could have rendered a random arrangement that would make assemblage structure undetectable.

Temporal and spatial segregation in an assemblage of Afrotropical subterranean snakes

Niche partititioning patterns have not been studied so far in burrowing tropical snakes of the families Typhlopidae and Leptotyphlopidae. In this study, we analyze temporal (= monthly activity) and spatial (= habitat use) niche dimensions in three species of burrowing snakes from the Niger Delta, Nigeria. Null model analyses, using two randomization algorithms and 30 000 Monte Carlo permutations, showed that there was random resource partitioning patterns as for the spatial niche dimension. One species (Rhinotyphlops punctatus) clearly dominated in the sample, and appeared to be more habitat generalist than the others. All three species showed an uneven monthly activity, with peaks occurring by wet season, and statistically significant positive correlations between mean monthly rainfall and number of captured snakes. However, there were significantly negative correlations between mean monthly temperature and number of captured snakes in two of the three species (Rhinotyphlops congestus;Leptotyphlopscfr.sundewalli).

Dietary relationships among coexisting anuran amphibians: a worldwide quantitative review

Anuran amphibians have traditionally been considered suitable model organisms for community ecology studies. In this paper, we review and quantitatively re-analyze the original studies published on dietary relationships among anuran communities worldwide. We re-analyzed 33 independent communities from all continents, including data on prey numbers and/or prey volumes. All datasets underwent null model re-analysis using two randomization algorithms. In addition, logistic regression models were used to identify specific assemblage patterns. We discovered three main patterns: (1) one particular algorithm (RA2, which replaces every cell in the matrix with one randomly chosen, but retains the zero structure of the matrix) performed much better at uncovering community structure; (2) nonrandom structure was more likely to occur in tropical than in nontropical regions; (3) prey volume was a better descriptor of dietary relationships than prey number when attempting to detect nonrandom structure. We showed that: pattern (1) depended on both the overall generalist nature of the anurans in general and on the mathematical properties of RA2; pattern (2) was consistent with theoretical attributes of tropicality; and pattern (3) was due to the intrinsic ecological properties of generalist organisms, which forage more or less opportunistically on prey of very different sizes; hence, when prey number is used as a diet descriptor, there is a risk of approximating different prey taxa that make different relative volume contributions to the overall diet as being of similar relevance .