Competition For Food Resources Research Articles

Dietary relationships among Nearctic and Neotropical migratory shorebirds in a key coastal wetland of South America

Dietary requirements influence the structure of shorebird assemblages, and information on diet is a key to understanding why and when particular species of shorebird use an area and how competition for food might shape their geographical distributions. We describe the diet and patterns of use of food resources of four migratory shorebirds at Samborombón Bay, Argentina, one of the most important sites for shorebirds in the western hemisphere. The birds consumed items representing at least 15 taxa but only a few taxa comprised the main resources consumed. The four species of shorebird showed dietary flexibility influenced by season and tidal level. Co-occurring species showed complementary differentiation in two dimensions of their respective trophic niches (taxonomic composition, size-class). The greatest differences in taxonomic composition of the diet were between Red Knots, which fed mainly on molluscs, and the other three species, which fed mainly on polychaetes. Polychaete consumers that co-occurred during autumn (Hudsonian Godwit and White-rumped Sandpiper) focussed on different prey sizes. Alternatively, shorebirds that co-occurred during winter (Hudsonian Godwits and Two-banded Plovers) fed mainly on polychaete of similar size but showed differences in the taxonomic composition of their diets. Interspecific competition for food resources might shape the composition of the shorebird assemblage of our study area during the austral autumn and winter.

Male competition fitness landscapes predict both forward and reverse speciation.

Speciation is facilitated when selection generates a rugged fitness landscape such that populations occupy different peaks separated by valleys. Competition for food resources is a strong ecological force that can generate such divergent selection. However, it is unclear whether intrasexual competition over resources that provide mating opportunities can generate rugged fitness landscapes that foster speciation. Here we use highly variable male F2 hybrids of benthic and limnetic threespine sticklebacks, Gasterosteus aculeatus Linnaeus, 1758, to quantify the male competition fitness landscape. We find that disruptive sexual selection generates two fitness peaks corresponding closely to the male phenotypes of the two parental species, favouring divergence. Most surprisingly, an additional region of high fitness favours novel hybrid phenotypes that correspond to those observed in a recent case of reverse speciation after anthropogenic disturbance. Our results reveal that sexual selection through male competition plays an integral role in both forward and reverse speciation.

Foods, macronutrients and fibre in the diet of blue sheep (Psuedois nayaur) in the Annapurna Conservation Area of Nepal.

Food resources are often critical regulating factors affecting individual fitness and population densities. In the Himalayan Mountains, Bharal "blue sheep" (Pseudois nayaur) are the main food resource for the endangered snow leopard (Panthera uncia), as well as being preyed upon by other predators. Blue sheep, however, may face a number of challenges including food resource competition with other wild and domestic ungulates, and hunting pressure. Here, we characterized the diet of blue sheep in the Annapurna Conservation Area (ACA) of Nepal and conducted proximate nutritional analysis on a limited number of plants identified as foods. Furthermore, we investigated the macronutrient and fiber balance of these plants using nutritional geometry which is a state-space approach to modeling multidimensional and interactive nutritional aspects of foraging. A total of 19 plant species/genera were identified in blue sheep pellets using microhistological analysis. On average, across seasons and regions of the study area, the two most frequently occurring plants in pellets were graminoids: Kobressia sp. and Carex spp. The macronutrient balance of Kobresia sp. was relatively high in carbohydrate and low in protein, while other plants in the diet were generally higher in protein and lipid content. Analysis of fiber balance showed that the two most consumed plants of blue sheep (i.e., Kobresia spp. and Carex spp.) contained the highest concentration of hemicellulose, which is likely digestible by blue sheep. The hemicellulose and lignin balance of plants ranged relatively widely, yet their cellulose contents showed less variation. Foraging by blue sheep may therefore be a balance between consuming highly digestible high-carbohydrate plants and plants less-digestible but higher in protein and/or lipid.

A proactive–reactive syndrome affects group success in an ant species

Social insects have been particularly evolutionarily successful: they dominate terrestrial ecosystems all over the globe. Their success stems from their social organization, where one or a few individuals reproduce, whereas others carry out different colony tasks. From an evolutionary standpoint, social species are particularly interesting because natural selection acts at both the individual and colony levels. Therefore, we might expect to see selection acting simultaneously on personality at the individual level and colony level. In this study, we tested whether captive colonies of the ant Aphaenogaster senilis exhibited different behavioral types and evaluated their consequences for intraspecific competition. Our results demonstrate that colonies of the same age exposed to standardized laboratory conditions did indeed have different personalities. In addition, we found that A. senilis demonstrated a behavioral syndrome that included proactive and reactive behaviors: colonies varied in their approaches to exploration, risk taking, food retrieval, and conspe-cific interactions. This syndrome appears to be associated with a trade-off between competition for food resources and temperature-related foraging risks. Bold colonies contained individuals who more readily explored novel environments, exhibited aggressive behaviors, and demonstrated higher food-retrieval efficiency during intraspecific competition trials. However, such colonies were also more risk prone: workers suffered higher mortality rates because they more frequently foraged over their critical thermal maximum. The trade-off we observed under laboratory conditions might be key in maintaining colony-level personality, thus driving local-level adaptations in collective behavior.

Dietary overlap and potential competition in a dynamic ungulate community in Northwestern Canada

ABSTRACTThe potential for interspecific competition for food resources is a key consideration when newly introduced ungulates occupy a shared range with resident native species. Management plans in Yukon, Canada, for reintroduced bison (Bison bison) and introduced elk (Cervus canadensis) called for an assessment of competition for food resources between these species and resident populations of caribou (Rangifer tarandus), thinhorn sheep (Ovis dalli), and moose (Alces americanus). To assess potential competition among ungulates, we examined dietary overlap of 7 ungulate species in southwestern Yukon, Canada. We compared diet composition at the forage class level and composite diet indices (diversity, evenness, and niche breadth) among species found at 2 elevation classes (high [≥1,200 m ASL] and low [<1,200 m ASL]) during summer and winter, using data derived from microhistological analyses of feces. Composite indices and percent of key forage classes in diets differed among ungulates during summer and winter and at both high and low elevations. Potential dietary overlap for most species pairs was low to moderate (0.07–0.60). However, for bison and thinhorn sheep at high elevations, and bison and semi‐feral horses (Equus ferus caballus) at low elevations, it was high (0.82–0.97) during both summer and winter, indicating potential for food competition. Dietary overlap between species appeared to be based primarily on morphophysiological classification (i.e., browser‐intermediate‐grazer), rather than body size. Bison, horses, and sheep were all grazers. Intermediate species, such as introduced elk, had only moderate dietary overlap with several species. We concluded that the potential for competition for food resources based on dietary overlap between bison and sheep and bison and horses may be high in our study area, depending on forage availability, but for all other species pairs in our study area the potential for forage competition is low to moderate. © 2015 The Wildlife Society.

Were large carnivorans and great climatic shifts limiting factors for hominin dispersals? Evidence of the activity of Pachycrocuta brevirostris during the Mid-Pleistocene Revolution in the Vallparadís Section (Vallès-Penedès Basin, Iberian Peninsula)

Abstract The chronology of the first human dispersal out of Africa and the ecological role of the genus Homo in Europe as a scavenger or an active hunter during the late Early Pleistocene are two of the paleoanthropological topics most hotly debated during the last decades. The earliest human occurrences in Western Europe are recorded in the Iberian Peninsula by the late Villafranchian (1.4–1.2 Ma), during a period of climatic stability. However, currently available taphonomic and paleoecological data suggest a direct and intense competition for food resources between these human populations and the large scavenging hyaenid Pachycrocuta brevirostris. The Villafranchian was followed by the Epivillafranchian (ca. 1.2–0.8 Ma), a period of climatic instability dominated by several strong glacial periods. The evidence from the Vallparadis Section reported here suggests that such unstable climatic conditions did not affect to a great extent the composition of the large mammal assemblages and, particularly, that of the carnivore guild. Based on the impressive record of carnivoran remains recovered from the Vallparadis Section and the taphonomic interpretation of this assemblage, we suggest that the putative direct competition between early Homo and large carnivores, especially P. brevirostris, persisted throughout the late Villafranchian and the Epivillafranchian.

Isotopic niches of sympatric native and exotic fish species in a Neotropical floodplain.

This study investigated the isotopic niches of two fish species, one exotic and one native. It was hypothesized that these species would show little or no isotopic niche overlap. This hypothesis was tested with the isotopic niche concept and the trophic Layman's metrics. A considerable isotopic niche overlap was observed between the species, mainly for the exotic that showed the greater percentage of overlapping, indicating an interspecific competition for food resources. Layman's metrics also showed this species probably exploits a more specific array of food resources when compared with the native species. The native species probably has the ability to exploit a wider array of resources, highlighted by the higher values given for the Layman's metrics. The juveniles and adults of native species showed minor overlapping between the isotopic niches. This indicates that they have probably adopted different foraging strategies, minimizing intraspecific competition. Evidences that the exotic species explores a narrower range of resources and that the native species has a greater isotopic niche and possibly suffer less intraspecific competition, indicates that the native species can tolerate the presence of the exotic species and promote survival and maintenance of its population even under possible competition effects imposed by the exotic species.

Evolution of hypsodonty reveals a long‐standing ecological separation in the Japanese shrew‐moles

AbstractHabitat segregation has been reported for the Japanese shrew‐moles by several studies. However, there is a lack of surveys aimed at characterizing the ecological separation occurring between Urotrichus talpoides and Dymecodon pilirostris. In this paper, possible reasons for this ecological separation are proposed for the first time. A geometric morphometrics analysis was performed on first lower molars and mandibles of both fossil and extant specimens. The results evidenced that U. talpoides evolved a hypsodont configuration and a more robust mandible bearing an enlarged second incisor, while D. pilirostris maintained the primitive brachyodont morphology and a slender mandible. The fossil specimens proved to be very similar to their extant relatives. The shape analyses of m1 and the mandible suggest that U. talpoides possesses a more efficient feeding behaviour compared with that of D. pilirostris. Moreover, the derived state of the mandible morphology, associated with a larger size, suggests that U. talpoides largely displaced D. pilirostris and confined it to isolated highland areas by means of competition for food resources.

DNA metabarcoding diet analysis for species with parapatric vs sympatric distribution: a case study on subterranean rodents.

Closely related sympatric species commonly develop different ecological strategies to avoid competition. Ctenomys minutus and C. flamarioni are subterranean rodents parapatrically distributed in the southern Brazilian coastal plain, showing a narrow sympatric zone. To gain understanding on food preferences and possible competition for food resources, we evaluated their diet composition performing DNA metabarcoding analyzes of 67 C. minutus and 100 C. flamarioni scat samples, collected along the species geographical ranges. Thirteen plant families, mainly represented by Poaceae, Araliaceae, Asteraceae and Fabaceae, were identified in the diet of C. minutus. For C. flamarioni, 10 families were recovered, with a predominance of Poaceae, Araliaceae and Asteraceae. A significant correlation between diet composition and geographical distance was detected in C. minutus, whereas the diet of C. flamarioni was quite homogeneous throughout its geographical distribution. No significant differences were observed between males and females of each species. However, differences in diet composition between species were evident according to multivariate analysis. Our results suggest some level of diet partitioning between C. flamarioni and C. minutus in the sympatric region. While the first species is more specialized on few plant items, the second showed a more varied and heterogeneous diet pattern among individuals. These differences might have been developed to avoid competition in the region of co-occurrence. Resource availability in the environment also seems to influence food choices. Our data indicate that C. minutus and C. flamarioni are generalist species, but that some preference for Poaceae, Asteraceae and Araliaceae families can be suggested for both rodents.

Anthropogenic food use and diet overlap between red foxes (Vulpesvulpes) and arctic foxes (Vulpeslagopus) in Prudhoe Bay, Alaska

Red foxes (Vulpes vulpes (L., 1758)) recently expanded into the oil fields at Prudhoe Bay, Alaska, USA, and we hypothesized that the availability of anthropogenic foods may contribute to their success and persistence there. This study assessed the importance of anthropogenic foods to the diets of red foxes and arctic foxes (Vulpes lagopus (L., 1758)), and competition for food resources between the two species in Prudhoe Bay. We used stable isotope analysis of fox tissues to infer diet during summer and winter for both red and arctic foxes, and lifetime diet for red fox. While the contribution of anthropogenic foods in late summer for both species’ diets was low (~10% to 15%), the contribution in late winter was higher and varied between species (red foxes = 49%; arctic foxes = 39%). Estimates of lifetime diet in red foxes suggest consistent use of anthropogenic foods. We found moderate overlap of fox diets, although red foxes appeared to be more specialized on lemmings, whereas arctic foxes had a more diverse diet. Availability and consumption of anthropogenic foods by red foxes, particularly in winter, may partially explain their year-round presence in Prudhoe Bay.

Fine-scale spatial age segregation in the limited foraging area of an inshore seabird species, the little penguin

Competition for food resources can result in spatial and dietary segregation among individuals from the same species. Few studies have looked at such segregations with the combined effect of sex and age in species with short foraging ranges. In this study we examined the 3D spatial use of the environment in a species with a limited foraging area. We equipped 26 little penguins (Eudyptula minor) of known age, sex, and breeding output with GPS (location) and accelerometer (body acceleration and dive depth) loggers. We obtained dietary niche information from the isotopic analysis of blood tissue. We controlled for confounding factors of foraging trip length and food availability by sampling adults at guard stage when parents usually make one-day trips. We observed a spatial segregation between old (>11 years old) and middle-aged penguins (between 5 and 11 years old) in the foraging area. Old penguins foraged closer to the shore, in shallower water. Despite observing age-specific spatial segregation, we found no differences in the diving effort and foraging efficiency between age classes and sexes. Birds appeared to target similar prey types, but showed age-specific variation in their isotopic niche width. We hypothesize that this age-specific segregation was primarily determined by a "cohort effect" that would lead individuals sharing a common life history (i.e. having fledged and dispersed around the same age) to forage preferentially together or to share similar foraging limitations.

An experimental study of Aurelia aurita feeding behaviour: Inference of the potential predation impact on a temperate estuarine nursery area

Temperate estuaries are nursery areas for economically important fisheries resources. The common jellyfish Aurelia aurita is a resident species in many of these areas, where it can reach high abundances. This work aimed to determine the potential for predation of A. aurita on zooplanktonic organisms and early life stages of fishes, measuring feeding rates at concentrations that mimic those occurring for zooplankton, fish eggs and larvae in an estuarine nursery area. A set of experiments was aimed at determining the feeding selectivity of jellyfish when offered a mixture of fish eggs and larvae and wild plankton. Clearance rates varied markedly with prey availability and concentrations. When given mixtures of different prey types, jellyfish preferentially elected some taxa (copepods and fish eggs). Data obtained in the laboratory experiments were used to infer the potential impact of jellyfish predation upon zooplankton and ichthyoplankton in the Guadiana estuary (Southern Iberia). Repeated sampling of zooplankton, fish eggs and medusae was undertaken during the summer season of 2011. Abundance determinations were combined with experimentally estimated clearance rates of individual medusa to infer the potential jellyfish-induced mortality on prey in the area. In June and early August jellyfish-induced mortality rates were very high, and half-life times (t1/2) were consequently short for the zooplankton and ichthyoplankton. Although the potentially overestimation of our feeding rates typical of confined laboratory experiments, the results show high ingestion and clearance rates at high temperatures, typical from summer condition, and results also suggest that either by predation on early life stages of fish, or by competition for food resources, jellyfish may have a significant impact on estuarine communities and its nursery function.

Interactions between multiple large macrofauna species and nematode communities — Mechanisms for indirect impacts of trawling disturbance

Diverse assemblages of infauna in sediments provide important physical and biogeochemical services, but are under increasing pressure by anthropogenic activities, such as benthic trawling. It is known that trawling disturbance has a substantial effect on the larger benthic fauna, with reductions in density and diversity, and changes in community structure, benthic biomass, production, and bioturbation and biogeochemical processes. Largely unknown, however, are the mechanisms by which the trawling impacts on the large benthic macro- and megafauna may influence the smaller meiofauna. To investigate this, a mesocosm experiment was conducted whereby benthic nematode communities from a non-trawled area were exposed to three different densities (absent, low, normal) of 7 large (>10mm) naturally co-occurring, bioturbating species which are potentially vulnerable to trawling disturbance. The results showed that total abundances of nematodes were lower if these large macrofauna species were present, but no clear nematode abundance effects could be assigned to the macrofauna density differences. Nematode community structure changed in response to macrofauna presence and density, mainly as a result of the reduced abundance of a few dominant nematode species. Any detectable effects seemed similar for nearly all macrofauna species treatments, supporting the idea that there may be a general indirect, macrofauna-mediated trawling impact on nematode communities. Explanations for these results may be, firstly, competition for food resources, resulting in spatial segregation of the meio- and macrobenthic components. Secondly, different densities of large macrofauna organisms may affect the nematode community structure through different intensities of bioturbatory disturbance or resource competition. These results suggest that removal or reduced densities of larger macrofauna species as a result of trawling disturbance may lead to increased nematode abundance and hints at the validity of interference competition between large macrofauna organisms and the smaller meiofauna, and the energy equivalence hypothesis, where a trade-off is observed between groups of organisms that are dependent on a common source of energy.

Aggression and Food Resource Competition between Sympatric Hermit Crab Species

The vertical zonation patterns of intertidal organisms have been topics of interest to marine ecologists for many years, with interspecific food competition being implicated as a contributing factor to intertidal community organization. In this study, we used behavioral bioassays to examine the potential roles that interspecific aggression and food competition have on the structuring of intertidal hermit crab assemblages. We studied two ecologically similar, sympatric hermit crab species, Clibanarius digueti [1] and Paguristes perrieri [2], which occupy adjacent zones within the intertidal region of the Gulf of California. During the search phase of foraging, C. digueti showed higher frequencies of aggressive behaviors than P. perrieri. In competition assays, C. digueti gained increased access to food resources compared to P. perrieri. The results suggest that food competition may play an important role in structuring intertidal hermit crab assemblages, and that the zonation patterns of Gulf of California hermit crab species may be the result of geographical displacement by the dominant food competitor (C. digueti).

Are Estuarine Fish Opportunistic Feeders? The Case of a Low Anthropized Nursery Ground (the Canche Estuary, France)

Stomach contents of the main fish species (i.e. sprat Sprattus sprattus, sea-bass Dicentrarchus labrax, common goby Pomatoschistus microps and flounder Platichthys flesus) in the Canche nursery ground (France) were examined from May 2006 to March 2007 according to food availability (i.e. macrozoobenthos and zooplankton) to analyse diet composition, trophic competition and prey selection. Overall, 44 prey fish species were identified from the 684 stomach contents examined. Fish diet was characterized by a wide diversity of prey, a relatively high feeding activity (vacuity index ranged between 16.9 and 29.0 % according to species) and spatiotemporal changes, except for D. labrax which did not vary between periods or estuarine zones. Copepods Temora longicornis and Euterpina acutifrons were the most important items in the diet of S. sprattus; for D. labrax, the dominant prey was the amphipod Gammarus sp., while Platichthys flesus and Pomatoschistus microps showed a more similar trophic niche (similarity percentage = 39 %) with diets consisting of nematodes and amphipods. Spatiotemporal sharing of trophic resources by fish and high food resources in the Canche estuary was examined, and very limited diet overlap was observed, indicating that competition for food resources was limited. Differences between the available preys and fish diets demonstrated that fish do not select the most abundant food resources. S. sprattus showed a selection for Tachidius sp. and cladocerans; D. labrax for Gammarus sp., Hediste diversicolor and to a lesser extent nematodes and Corophium sp.; Pomatoschistus microps for nematodes and Gammarus sp.; and Platichthys flesus for nematodes, Gammarus sp., H. diversicolor and Corophium sp. It was concluded that the studied fish exhibit a specialist rather than opportunistic feeding strategy.

Changes in roach (Rutilus rutilus (L.)) diet and growth in relation to river water quality

Diet composition and growth of the roach (Rutilus rutilus (L.)) was studied in three Lithuanian rivers, differing in water quality. In the pristine river roach fed on various taxa of macroinvertebrates and plant material with similar frequency, none of food categories clearly dominated in the guts of fish. The overall diversity of food items in the diet as well as abundance and diversity of macroinvertebrates in the benthic assemblages were the greatest in the moderately polluted river, but plant material formed the major part of food and was consumed most frequently, presumably as a result of inter-specific competition for the food resources. Percentage of the plant material in the diet was the smallest in the heavily polluted river, where roach predominated over the rest of fish. The growth rates of roach did not differ among reference and heavily polluted river, but in the moderately polluted river fish grew much slower. It is likely that habitat degradation to an extent when majority of less tolerant fish and macroinvertebrate species do not survive seems to be favorable for roach, if the degradation reduces inter-specific competition for food resources.

Physiological indices as indicators of ecosystem status in shellfish aquaculture sites

The filtration activity of cultured mussels may exert a strong control on phytoplankton populations. Given that phytoplankton constitutes the base of marine food webs, carrying capacity in shellfish aquaculture sites has been commonly studied in terms of phytoplankton depletion. However, spatial and temporal variability of phytoplankton concentration in coastal areas present a methodological constraint for using phytoplankton depletion as an indicator in monitoring programs, and necessitates intensive field campaigns. The main goal of this study is to explore the potential of different bivalve performance indices for use as alternatives to phytoplankton depletion as cost-effective indicators of carrying capacity. For that, a fully spatial hydrodynamic–biogeochemical coupled model of Tracadie Bay, an intensive mussel culture embayment located in Prince of Edward Island (Canada), has been constructed and scenario building has been used to explore the relationship between phytoplankton depletion and bivalve performance. Our underlying premise is that overstocking of bivalves leads to increased competition for food resources, i.e. phytoplankton, which may ultimately have a significant effect on bivalve growth rate and performance. Following this working hypothesis, the relationships among bay-scale phytoplankton depletion and three bivalve physiological indices, one static, condition index, and two dynamic, tissue mass and shell length growth rates, have been simulated. These three metrics present methodological advantages compared to phytoplankton depletion for incorporation into monitoring programs. Although significant correlations among phytoplankton depletion and the three physiological indices have been observed, shell length growth rate is shown as the most sensitive indicator of carrying capacity, followed by tissue mass growth rate and then by condition index. These results demonstrate the potentiality of using bivalve physiological measurements in monitoring programs as indicators of ecosystem status.

Colony size and not nest density drives reproductive output in the Common TernSterna hirundo

Density is known to be an important factor in population size regulation. Several mechanisms of density limitation have been identified in colonial birds. We studied competition in Common Terns Sterna hirundo to assess whether the factor limiting reproductive output was competition for nest‐sites, which is dependent on local nest density, or density‐dependent competition for food resources, which is dependent on overall colony size using the same foraging area. We found strong associations of both colony size and nest density with reproductive output in five colonies of Common Terns in three different habitats (one marine, two freshwater). Based on detailed long‐term datasets of six separate sub‐colonies of the Banter See colony that differed in nest density, we found that reproductive success was not related to nest density but to overall colony size, possibly a result of resource depletion and food competition. We also found carry‐over effects of colony size during rearing on post‐fledging return rate. These results have important implications for the conservation management plans aimed at recovering declining populations of Common Terns.

Dietary niche partitioning in sympatric gadid species in coastal Newfoundland: evidence from stomachs and C-N isotopes

The feeding habits of co-occurring gadid species Atlantic cod (Gadus morhua) and Greenland cod (Gadus ogac) in coastal Newfoundland waters, examined using stable isotope (δ 13C and δ 15N) and stomach content analysis, indicated little dietary niche overlap and interspecific competition for food resources despite similar trophic levels. Both species consumed a variety of invertebrates and fish but showed a preference for different prey items. Polychaetes, fish and small crustaceans dominated G. ogac stomach contents while small crustaceans, in particular hyperiid amphipods and fish, dominated those of G. morhua. In general, G. morhua consumed more pelagic prey and had a significantly more pelagic (more negative) δ 13C signature while G. ogac consumed primarily benthic prey and had a more benthic (more positive) δ 13C signature. δ 15N levels were similar in these species suggesting similar trophic positions, with levels increasing with fish length in both species. Dietary overlap was not significant in both stomach and stable isotope analyses. We conclude that interspecific competition for food is low between G. ogac and G. morhua and is unlikely to be a factor in the slow rebuilding of Atlantic cod in this region.

Giant lizards occupied herbivorous mammalian ecospace during the Paleogene greenhouse in Southeast Asia

Mammals dominate modern terrestrial herbivore ecosystems, whereas extant herbivorous reptiles are limited in diversity and body size. The evolution of reptile herbivory and its relationship to mammalian diversification is poorly understood with respect to climate and the roles of predation pressure and competition for food resources. Here, we describe a giant fossil acrodontan lizard recovered with a diverse mammal assemblage from the late middle Eocene Pondaung Formation of Myanmar, which provides a historical test of factors controlling body size in herbivorous squamates. We infer a predominately herbivorous feeding ecology for the new acrodontan based on dental anatomy, phylogenetic relationships and body size. Ranking body masses for Pondaung Formation vertebrates indicates that the lizard occupied a size niche among the larger herbivores and was larger than most carnivorous mammals. Paleotemperature estimates of Pondaung Formation environments based on the body size of the new lizard are approximately 2–5°C higher than modern. These results indicate that competitive exclusion and predation by mammals did not restrict body size evolution in these herbivorous squamates, and elevated temperatures relative to modern climates during the Paleogene greenhouse may have resulted in the evolution of gigantism through elevated poikilothermic metabolic rates and in response to increases in floral productivity.