Predator-prey interactions: jaguar predation on caiman in a floodplain forest

Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle

The lifestyle of spinosaurid dinosaurs has been a topic of lively debate ever since the unveiling of important new skeletal parts for Spinosaurus aegyptiacus in 2014 and 2020. Disparate lifestyles for this taxon have been proposed in the literature; some have argued that it was semiaquatic to varying degrees, hunting fish from the margins of water bodies, or perhaps while wading or swimming on the surface; others suggest that it was a fully aquatic underwater pursuit predator. The various proposals are based on equally disparate lines of evidence. A recent study by Fabbri and coworkers sought to resolve this matter by applying the statistical method of phylogenetic flexible discriminant analysis to femur and rib bone diameters and a bone microanatomy metric called global bone compactness. From their statistical analyses of datasets based on a wide range of extant and extinct taxa, they concluded that two spinosaurid dinosaurs (S. aegyptiacus, Baryonyx walkeri) were fully submerged "subaqueous foragers," whereas a third spinosaurid (Suchomimus tenerensis) remained a terrestrial predator. We performed a thorough reexamination of the datasets, analyses, and methodological assumptions on which those conclusions were based, which reveals substantial problems in each of these areas. In the datasets of exemplar taxa, we found unsupported categorization of taxon lifestyle, inconsistent inclusion and exclusion of taxa, and inappropriate choice of taxa and independent variables. We also explored the effects of uncontrolled sources of variation in estimates of bone compactness that arise from biological factors and measurement error. We found that the ability to draw quantitative conclusions is limited when taxa are represented by single data points with potentially large intrinsic variability. The results of our analysis of the statistical method show that it has low accuracy when applied to these datasets and that the data distributions do not meet fundamental assumptions of the method. These findings not only invalidate the conclusions of the particular analysis of Fabbri et al. but also have important implications for future quantitative uses of bone compactness and discriminant analysis in paleontology.

Collaborative behaviour and coalitions in male jaguars (Panthera onca)—evidence and comparison with other felids

Abstract

Most large felids are classified as solitary species, with only lions (Panthera leo) and cheetahs (Acinonyx jubatus) exhibiting social, collaborative behaviours. Herein, we present evidence of the formation of male coalitions by jaguars (Panthera onca), based on data from five studies conducted with camera trapping, GPS telemetry, and direct observations in the Venezuelan Llanos and Brazilian Pantanal. Out of 7062 male records obtained with camera traps or visual observations, we detected 105 cases of male-male interactions, of which we classified 18 as aggression, nine as tolerance, 70 as cooperation/coalition, and eight as unidentified. In two studies, two male jaguars formed stable coalitions lasting over 7 years each. In the Llanos, each coalition male paired and mated with several females. For male jaguar coalitions, we documented similar behaviours as recorded earlier in lions or cheetahs, which included patrolling and marking territory together, invading territories of other males, collaborative chasing and killing other jaguars, and sharing prey. However, different from lions or cheetahs, associated male jaguars spent less time together, did not cooperate with females, and did not hunt cooperatively together. Our analysis of literature suggested that male jaguar coalitions were more likely to form when females had small home range size, a proxy of females’ concentration, while in lions, the male group size was directly correlated with the female group size. Similarly, locally concentrated access to females may drive formation of male coalitions in cheetahs. We conclude that high biomass and aggregation of prey are likely drivers of sociality in felids.

Significance statement

The division into social and solitary species in large felids has so far seemed unambiguous, with only lions and cheetahs classified as social species, in which male coalitions also occurred. Our data show that, under certain conditions, male coalitions may also form in jaguar populations. Factors that drive formation of male coalitions in lions and cheetahs, but not in other species of large cats, have not been clear until now. Our analyses indicate that in jaguars, lions, and cheetahs, the concentration of females likely plays the most important role. In jaguars, the probability of male coalition occurrence is highest in populations with the smallest mean female home range size (and thus likely high local density of females), while in lions, male group size is most strongly correlated with female group size.

Density and habitat use of one of the last jaguar populations of the Brazilian Atlantic Forest: Is there still hope?

The jaguar (Panthera onca) plays an important role in maintaining biodiversity and ecological processes. We evaluated the status of a jaguar population in one of the last stronghold habitats for its conservation in the Atlantic Forest, the Rio Doce State Park (RDSP). We used a random survey design from 2016/17 to estimate jaguar abundance and density as well as its occupancy and detection probabilities in the entire Park's area. To monitor for temporal fluctuations in density and abundance, we used a systematic survey design in the southern portion of the Park where jaguars were more recorded when using the random approach. We then conducted two surveys in 2017/18 and 2020. Our 2016/17 random survey revealed that jaguar density (0.11 ± SE 0.28 individuals/100 km2) was the lowest obtained for the species across the Atlantic Forest. We noticed that jaguar density increased three times from 2017/18 (0.55 ± SE 0.45 individuals/100 km2) to 2020 (1.61 ± SE 0.6 individuals/100 km2). Jaguar occupancy and detection probability were 0.40 and 0.08, respectively. The low jaguar occupancy probability was positively associated with smaller distances from lakes and records of potential prey. The detection probability was positively associated with prey detection, the rainy season, and smaller distances from lakes. Our work contributes to a growing awareness of the potential conservation value of a protected area in a human-dominated landscape as one of the last strongholds for jaguars across the Atlantic Forest.

Amazon islands as predator refugia: jaguar density and temporal activity in Maracá-Jipioca

Limited space on islands usually cannot sustain stable populations of large predators. However, jaguars, the largest cat species in the Americas, unexpectedly occur in the Estação Ecológica Maracá-Jipioca reserve, a system of continental Amazonian islands in the Atlantic Ocean. We investigated jaguar population structure, density, and activity patterns. We placed 25 camera-trap stations across 149.19 km2 and used spatially explicit capture–recapture to estimate density, and Rayleigh’s test to assess activity patterns. We identified 21 individuals (12 females, six males, and three cubs) and estimated an adult density of 6.7 individuals per 100 km2, which equals a population of approximately 43 jaguars. The population is composed mostly of females (66%) in relation to males (33%). Male and female activity patterns overlapped and showed more activity during daytime. The high jaguar density and the presence of females with cubs indicate that these islands are likely natural refugia for jaguars, reinforcing the importance of this protected area for jaguar conservation and possibly challenging the paradigm that large-mammal populations are not feasible in restricted islands.

Early life differences in behavioral predispositions in two Alligatoridae species

Behavioral predispositions are innate tendencies of animals to behave in a given way without the input of learning. They increase survival chances and, due to environmental and ecological challenges, may vary substantially even between closely related taxa. These differences are likely to be especially pronounced in long-lived species like crocodilians. This order is particularly relevant for comparative cognition due to its phylogenetic proximity to birds. Here we compared early life behavioral predispositions in two Alligatoridae species. We exposed American alligator and spectacled caiman hatchlings to three different novel situations: a novel object, a novel environment that was open and a novel environment with a shelter. This was then repeated a week later. During exposure to the novel environments, alligators moved around more and explored a larger range of the arena than the caimans. When exposed to the novel object, the alligators reduced the mean distance to the novel object in the second phase, while the caimans further increased it, indicating diametrically opposite ontogenetic development in behavioral predispositions. Although all crocodilian hatchlings face comparable challenges, e.g., high predation pressure, the effectiveness of parental protection might explain the observed pattern. American alligators are apex predators capable of protecting their offspring against most dangers, whereas adult spectacled caimans are frequently predated themselves. Their distancing behavior might be related to increased predator avoidance and also explain the success of invasive spectacled caimans in the natural habitats of other crocodilians.

Factors influencing the habitat use by ocelots in one of the last large Atlantic Forest remnants in southeastern Brazil

Ocelots (Leopardus pardalis) are widely distributed throughout the Americas, being dependent on forested areas to survive. Although ocelot ecology is broadly studied throughout the species range distribution, studies concerning factors that may affect ocelot occupancy in the Atlantic Forest are still scarce. We used camera traps to evaluate factors influencing the probabilities of detection and occupancy of ocelots in a protected area of the Atlantic Forest, the Rio Doce State Park (RDSP), southeastern Brazil. To assess ocelot occupancy and detection probabilities, we measured the distances between sampling stations and rivers, lakes, cities, pasture, and Eucalyptus plantations. In addition, we recorded the mean rainfall levels for each sampling occasion, and native grassland areas within a 500 m-buffer around each sampling station. We found a strong and positive association between ocelot detection and the dry season, which might be due to a higher number of individuals moving through the Park during this season. Moreover, we found a strong and positive association of ocelot detection with native grassland areas around lakes, which may be related to the ocelot behavior of searching for prey in these areas. Conversely, the ocelot occupancy probability was intermediate ( Ψ ^  = 0.53, 95% CI = 0.36-0.69) and was not strongly associated with the evaluated covariates, which may be explained by the high-quality of forest habitats and water resources that are homogeneously distributed within the Park. Our study indicates that the RDSP still provides a structurally suitable forest habitat for ocelots, but because of the current worrying scenario of over fragmentation, reduction of forest cover, and weakness of the protective legislation of this biome, the long-term persistence of the species in RDSP is uncertain.

Wetlands are keystone habitats for jaguars in an intercontinental biodiversity hotspot

Agricultural development was the major contributor to South America's designation as the continent with the highest rates of forest loss from 2000-2012. As the apex predator in the Neotropics, jaguars (Panthera onca) are dependent on forest cover but the species' response to habitat fragmentation in heterogeneous agricultural landscapes has not been a subject of extensive research. We used occupancy as a measure of jaguar habitat use in Colombia's middle Magdalena River valley which, as part of the intercontinental Tumbes-Chocó-Magdalena biodiversity hotspot, is exceedingly fragmented by expanding cattle pastures and oil palm plantations. We used single-season occupancy models to analyze 9 months of data (2015-2016) from 70 camera trap sites. Given the middle Magdalena's status as a "jaguar corridor" and our possible violation of the occupancy models' demographic closure assumption, we interpreted our results as "probability of habitat use (Ψ)" by jaguars. We measured the associations between jaguar presence and coverage of forest, oil palm, and wetlands in radii buffers of 1, 3, and 5 km around each camera trap. Our camera traps recorded 77 jaguar detections at 25 of the camera trap sites (36%) during 15,305 trap nights. The probability of detecting jaguars, given their presence at a site, was 0.28 (0.03 SE). In the top-ranked model, jaguar habitat use was positively influenced by wetland coverage (β = 7.16, 3.20 SE) and negatively influenced by cattle pastures (β = -1.40, 0.63 SE), both in the 3 km buffers. We conclude that wetlands may serve as keystone habitats for jaguars in landscapes fragmented by cattle ranches and oil palm plantations. Greater focus on wetland preservation could facilitate jaguar persistence in one of the most important yet vulnerable areas of their distribution.

Jaguar Densities across Human-Dominated Landscapes in Colombia: The Contribution of Unprotected Areas to Long Term Conservation

Large carnivores such as jaguars (Panthera onca) are species of conservation concern because they are suffering population declines and are keystone species in their ecosystems. Their large area requirements imply that unprotected and ever-increasing agricultural regions can be important habitats as they allow connectivity and dispersal among core protected areas. Yet information on jaguar densities across unprotected landscapes it is still scarce and crucially needed to assist management and range-wide conservation strategies. Our study provides the first jaguar density estimates of Colombia in agricultural regions which included cattle ranching, the main land use in the country, and oil palm cultivation, an increasing land use across the Neotropics. We used camera trapping across two agricultural landscapes located in the Magdalena River valley and in the Colombian llanos (47-53 stations respectively; >2000 trap nights at both sites) and classic and spatially explicit capture-recapture models with the sex of individuals as a covariate. Density estimates were 2.52±0.46-3.15±1.08 adults/100 km2 in the Magdalena valley, whereas 1.12±0.13-2.19±0.99 adults/100 km2 in the Colombian llanos, depending on analysis used. We suggest that jaguars are able to live across unprotected human-use areas and co-exist with agricultural landscapes including oil-palm plantations if natural areas and riparian habitats persist in the landscape and hunting of both jaguar and prey is limited. In the face of an expanding agriculture across the tropics we recommend land-use planning, adequate incentives, regulations, and good agricultural practices for range-wide jaguar connectivity and survival.

Non-lethal sampling for mercury evaluation in crocodilians

Mercury (Hg) is a ubiquitous environmental contaminant that poses potential threats to ecosystems due to its toxicity to humans and wildlife. The development of non-lethal sampling techniques is a critical step for evaluation of Hg in threatened species in tropical floodplain environments, where most of Hg found is the result of land use and gold mining activities, and more methylation sites are available. We evaluated the spatial and seasonal effectiveness of caudal scutes and claws to estimate Hg bioaccumulation in crocodilians (Caiman yacare), in the scarcely documented Pantanal. Hence, we investigated the potential for Hg bioaccumulation in top predators according to its proximity to mining sites, and in water bodies with different hydrological characteristics and connectivity with the main river during two phases of the flood pulse (dry and flood). The highest Hg concentrations were detected in caimans captured close to mining activities, in claws (2176 ng g(-1) ww) and caudal scutes (388 ng g(-1) ww). THg concentration in claws was related to the flood season and its mean concentration was thirteen fold higher than Hg concentration in scutes during whole year. Both tissues were found to be effective as non-lethal sampling techniques for measuring Hg bioaccumulation in reptiles over time. Nevertheless, claw tissue seems to have a more consistent result, since its constitutional chemical characteristics makes it a better indicator of spatial patterns that influence on Hg exposure.

Lethal interactions among vertebrate top predators: a review of concepts, assumptions and terminology

Lethal interactions among large vertebrate predators have long interested researchers because of ecological and conservation issues. Research focusing on lethal interactions among vertebrate top predators has used several terms with a broad sense, and also introduced new terminology. We analysed the published literature with reference to the main underlying concepts and the use of terminology and its ecological context. The most frequently used terms in the literature were 'predation', 'intraguild predation', 'interference competition', and 'interspecific killing'. Most studies presented evidence of the killing of the victim (77%), but information regarding its consumption was not given in 48% of cases. More than half of the analysed studies (56%) had no solid information on the degree of competition between interacting species. By reviewing definitions and their underlying assumptions, we demonstrate that lethal interactions among large vertebrate predators could be designated using four terms-'predation', 'intraguild predation', 'interspecific competitive killing', and 'superpredation'-without the need to employ additional terminology that may increase confusion and misuse. For a correct framework of these lethal interactions it is critical to assess if the kill is consumed, if the victim is indeed a competitor of the killer, and if the prey is a high-order predator. However, these elements of the framework are simultaneously the most common constraints to studies of lethal interactions, since they often require a great effort to obtain. The proper use of terms and concepts is fundamental to understanding the causes behind lethal interactions and, ultimately, what is actually happening in these complex interactions.