Ecology and signal evolution in lizards

Current models of signal evolution explain diversity by invoking a variety of social, perceptual and environmental factors. Social systems and spacing patterns determine the active space of signals and their function. Receiver sensory systems and habitat characteristics interact to constrain signal design. These factors are traditionally implicated in promoting directional evolutionary change, leading to increases or decreases in signal complexity. We examine macro-evolutionary trends in signal design, as reflected by display modifier repertoire size, for 124 species of iguanian lizards to identify the importance of ecological factors in display evolution. Possessing a small home range, being arboreal and feeding on moving prey are all correlated with the evolution of large repertoires. However, living in closed habitats is associated with increased evolutionary change in repertoire size, producing greater signal diversity. Ecological factors can thus act either directionally or to promote evolutionary lability.   © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 127–148.     

Correlated evolution of thermal characteristics and foraging strategy in lacertid lizards

1. We investigated the association between field body temperatures (T_b), field air temperatures (T_a), and their differences (Δ) with measurements of foraging activity (percentage of time moving (PTM), number of movements per minute (MPM) and proportion of prey attacked while moving (PAM)) for 25 species of lacertid lizards.

2. Lizards active at relatively high field body temperatures tended to have higher PTM and PAM values. We found no association between temperatures and MPM. The difference Δ did not co-vary with PTM and MPM, but showed a positive trend with PAM.

3. Our results seem robust with regard to the assumptions of different models of evolution and to the phylogenetic trees used.

Evidence of constrained phenotypic evolution in a cryptic species complex of agamid lizards

Lineages that exhibit little morphological change over time provide a unique opportunity to explore whether nonadaptive or adaptive processes explain the conservation of morphology over evolutionary time scales. We provide the most comprehensive evaluation to date of the evolutionary processes leading to morphological similarity among species in a cryptic species complex, incorporating two agamid lizard species (Diporiphora magna and D. bilineata). Phylogenetic analysis of mitochondrial (ND2) and nuclear (RAG-1) gene regions revealed the existence of eight deeply divergent clades. Analysis of morphological data confirmed the presence of cryptic species among these clades. Alternative evolutionary hypotheses for the morphological similarity of species were tested using a combination of phylogenetic, morphological, and ecological data. Likelihood model testing of morphological data suggested a history of constrained phenotypic evolution where lineages have a tendency to return to their medial state, whereas ecological data showed support for both Brownian motion and constrained evolution. Thus, there was an overriding signature of constrained evolution influencing morphological divergence between clades. Our study illustrates the utility of using a combination of phylogenetic, morphological, and ecological data to investigate evolutionary mechanisms maintaining cryptic species.     

Above-ground biomass and vegetation attributes in the forest-savannah mosaic of Togo,West Africa

Despite the increasing interest in the role of African savannah and woodlands on the global carbon cycle, little is known about the above-ground biomass (AGB) and the factors affecting it in these ecosystems in West Africa. We estimated AGB in different vegetation types of a forest–savannah mosaic in Togo, and we investigated the relationship between AGB, structural and diversity attributes. We also assessed the effects of using the ≥5 or ≥10 cm diameter threshold on AGB estimates. We sampled tree diameter, height and species of all trees ≥5 cm diameter following standardised protocols in 160 plots of 50 × 20 m (50 × 10 m for riparian). Above-ground biomass (AGB) (all trees ≥5 cm diameter) ranged from 6.2 Mg/ha in shrub savannah to 292 Mg/ha in riparian forest and showed significant differences between vegetation types. Differences in AGB were related to structural attributes, with little influence of diversity attributes. The effects of minimum tree diameter size (5 or 10 cm) on AGB estimates were negligible. At a landscape level, closed-canopy and open forests stored important quantities of carbon. We highlight the importance of the forest–savannah mosaic as a large carbon pool, which could be released if converted to another land cover type.     

Interdemic variation in the foraging ecology of the African cyprinid, Barbus neumayeri

In the African cyprinid, Barbus neumayeri, populations from hypoxic waters have larger gills than populations from well-oxygenated streams. Differences in trophic morphology and feeding performance between these populations suggest a reduction in feeding efficiency in large-gilled fish that may reflect spatial constraints of the gills. However, this variation may also reflect interdemic variation in diets. In this study, we describe patterns of variation in diet, gut morphology, and prey availability for populations of B. neumayeri from swamp (low-oxygen) and stream (high-oxygen) sites in Kibale National Park, Uganda. Our results indicate that B. neumayeri are omnivorous, feeding primarily on benthic prey items; however, diets differed among swamp and stream sites for certain prey types. The observed dietary differences do not provide direct support for predictions based on variation in trophic musculature; hard-bodied prey were more common in low-oxygen sites. Prey availability also differed among sites; in particular, insect abundance and richness was generally lower in the swamp sites. Gut length was longer in one of the four populations, but did not conform to expectations based on diet differences. Condition and growth rates did not differ between populations from hypoxic and well-oxygenated sites, despite observed differences in prey availability and diet, suggesting that B. neumayeri may be distributed in a way that equalizes fitness among populations in different habitats.     

Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

A defining character of adaptive radiations is the evolution of a diversity of morphological forms that are associated with the use of different habitats, following the invasion of vacant niches. Island adaptive radiations have been thoroughly investigated but continental scale radiations are more poorly understood. Here, we use 52 species of Australian agamid lizards and their Asian relatives as a model group, and employ three‐dimensional geometric morphometrics to characterize cranial morphology and investigate whether variation in cranial shape reflects patterns expected from the ecological process of adaptive radiation. Phylogenetic affinity, evolutionary allometry, and ecological life habit all play major roles in the evolution of cranial shape in the sampled lizards. We find a significant association between cranial shapes and life habit. Our results are in line with the expectations of an adaptive radiation, and this is the first time detailed geometric morphometric analyses have been used to understand the selective forces that drove an adaptive radiation at a continental scale.     

Marine subsidies change short‐term foraging activity and habitat utilization of terrestrial lizards

Resource pulses are brief periods of unusually high resource abundance. While population and community responses to resource pulses have been relatively well studied, how individual consumers respond to resource pulses has received less attention. Local consumers are often the first to respond to a resource pulse, and the form and timing of individual responses may influence how the effects of the pulse are transmitted throughout the community. Previous studies in Bahamian food webs have shown that detritivores associated with pulses of seaweed wrack provide an alternative prey source for lizards. When seaweed is abundant, lizards (Anolis sagrei) shift to consuming more marine‐derived prey and increase in density, which has important consequences for other components of the food web. We hypothesized that the diet shift requires individuals to alter their habitat use and foraging activity and that such responses may happen very rapidly. In this study, we used recorded video observations to investigate the immediate responses of lizards to an experimental seaweed pulse. We added seaweed to five treatment plots for comparison with five control plots. Immediately after seaweed addition, lizards decreased average perch height and increased movement rate, but these effects persisted for only 2 days. To explore the short‐term nature of the response, we used our field data to parametrize heuristic Markov chain models of perch height as a function of foraging state. These models suggest a “Synchronized‐satiation Hypothesis,” whereby lizards respond synchronously and feed quickly to satiation in the presence of a subsidy (causing an initial decrease in average perch height) and then return to the relative safety of higher perches. We suggest that the immediate responses of individual consumers to resource pulse events can provide insight into the mechanisms by which these consumers ultimately influence community‐level processes.     

Decisions of cattle herdsmen in Burkina Faso and optimal foraging models

Models of optimal foraging theory are used to evaluate the decisions of a sedentary herdsman and his family in Burkina Faso concerning the movement of his cattle from pasture to pasture. Generally, such models describe exploitation at the patch level, but are inadequate at higher levels. The herdsmen in the study area are generally sedentary, and their strategy of exploitation appears to be characterized by planning at least in terms of a whole day and minimizing daily travel time among fields. In conjuction with this conclusion a modified optimization model is proposed. We conclude that optimal foraging models are useful in interpreting and understanding the rules governing the movements of traditional West African herdsmen when so modified, but that more data are needed to develop and test these models further.     

Life-history strategies of Australian lizards: a comparison between the tropics and the temperate zone

Summary Previous studies have suggested that tropical and temperate-zone lizards may differ fundamentally in life histories. We tested the applicability of this idea to Australian species by comparing temperate-zone species of agamid and scincid lizards with their congeners from the seasonal tropics. Data were derived from dissection of 1,941 specimens and from published information. Clutch size and egg size were positively correlated with mean maternal body size in most lizard species from both climatic zones. Mean body size of the lizards studies did not differ between the tropics and the temperate zone, nor did egg or hatchling size. However, tropical skinks showed considerably (approximately 20%) lower clutch size and relative clutch mass than did temperate-zone skinks. This difference was partly due to the higher incidence of species with low, invariant clutch size in the tropical lizard fauna (as seen in other continents as well), but primarily due to a trend for lineages (especially genera) with relatively high fecundity to be more common in the temperate zone than in the tropics. In contrast to studies on African lizards, our data suggested that modification of clutch size between areas has not occurred within genera: congeneric species from the tropics and temperate zone did not differ in clutch size. Production of more than one clutch per annum by individual females was common in both climatic zones. Tropical lizards may differ from temperate-zone species in showing higher reproductive frequencies, more rapid growth and earlier maturation. However, most of these effects may be due to phenotypic responses to environmental conditions (especially longer annual activity season), rather than to genetically based lifehistory adaptations.     

Optimal foraging constrains macroecological patterns: body size and dietary niche breadth in lizards

Aim  To explore and identify probable mechanisms contributing to the relationships among body size, dietary niche breadth and mean, minimum, maximum and range of prey size in predaceous lizards.
Location  Our data set includes species from tropical rainforests, semi-arid regions of Brazil, and from deserts of the south-western United States, Australia and the Kalahari of Africa.
Methods  We calculated phylogenetic and non-phylogenetic regressions among predator body size, dietary breath and various prey size measures.
Results  We found a negative association between body size and dietary niche breadth in 159 lizard species sampled across most evolutionary lineages of squamate reptiles and across major continents and habitats. We also show that mean, minimum, maximum and range of prey size were positively associated with body size.
Main conclusions  Our results suggest not only that larger lizards tend to eat larger prey, but in doing so offset their use of smaller prey. Reduction of dietary niche breadth with increased body size in these lizards suggests that large predators target large and more profitable prey. Consequently, the negative association between body size and niche breadth in predators most likely results from optimal foraging. Though this result may appear paradoxical and runs counter to previous studies, resources for predators may be predictably more limited than resources for herbivores, thus driving selection for more profitable prey.     

Ambush site selection and ontogenetic shifts in foraging strategy in a semi-aquatic pit viper, the Eastern cottonmouth

Although habitat selection has been studied in a variety of snake taxa, little is known about habitat selection in aquatic snake species. Additionally, due to their small size and secretive nature, juvenile snakes are seldom included in habitat selection studies. The Eastern cottonmouth Agkistrodon piscivorus is a semi-aquatic pit viper known to use ambush, sit-and-wait foraging strategies. Ambush hunters are likely to select habitats that increase opportunity for successful prey capture while minimizing predation risk and maintaining appropriate thermal and hydric conditions. We characterized the foraging strategy and microhabitat use of cottonmouths at Ellenton Bay, an isolated Carolina bay freshwater wetland on the Savannah River Site in SC, USA. We measured habitat characteristics of 55 ambush sites used by 51 individual cottonmouths located during nighttime visual surveys, as well as 225 randomly selected sites within our search area. Cottonmouths exhibited an ontogenetic shift in foraging strategy with juveniles using predominately ambush foraging around the edge of the wetland while adults were most often encountered actively moving within the wetland. Principal components analysis revealed that juveniles selected foraging microhabitats that were different from random and consisted of mud substrate with sparse vegetation, whereas adults occupied a greater variety of microhabitats that did not differ from random. Concomitantly, free-ranging cottonmouths exhibited ontogenetic shifts in diet: juveniles consumed mostly salamanders, while adults ate a greater variety of prey including other snakes and birds. Our results highlight the importance of understanding how ontogenetic changes in coloration, diet and predation risk influence foraging strategy and microhabitat selection in snakes.     

Spatial and trophic niche differentiation in two sympatric lizards (Tropidurus torquatus and Cnemidophorus ocellifer) with different foraging tactics

Abstract In a ‘restinga’ habitat of southeastern Brazil, we studied the food habits and the microhabitat use of two lizards with distinct foraging modes: the tropidurid Tropidurus torquatus, a sit-and-wait predator, and the teiid Cnemidophorus ocellifer, a wide forager. The diet of the two species differed strongly, indicating a low level of similarity in their trophic niche. The sit-and-wait predator fed mainly on mobile prey, whereas the wide forager fed mainly on sedentary prey (larvae). The spatial niche breadth of T. torquatus was larger than that of C. ocellifer. Despite interspecific differences, the two species overlapped greatly in micro-habitat use. The data indicate that at Linhares the two lizard species differed more in food resources than in microhabitat, and that most of the food differences reflect the foraging patterns of the species.     

Root foraging strategies and soil patchiness in a humid savanna

In Lamto (Côte d'Ivoire), the savanna is a patchy environment as far as soil is concerned: tree clumps and termite mounds lead to higher nutrient contents than in the surrounding savanna. Mature Borassus aethiopum (Mart.) specimens are tall palm trees dominating the community, with aerial parts located out of these nutrient-rich patches.Palm root densities were compared under tree clumps and in the surrounding savanna, and were also sampled along transects between palm trees and nutrient-rich patches (two clumps and one mound). Palm root densities were far higher (up to 10 times) in the nitrogen-rich soil of both clumps and termite mounds than in the surrounding savanna. Evidence is given that palm trees are able to extend their root system as far as 20 m towards these nutrient-rich patches where they proliferate. These results point out a particular root foraging strategy, which is one of the first known for a woody perennial. They also provide new insights for understanding nitrogen cycling and savannas high rate of primary production.     

Herpetofaunal communities at Muni Lagoon in Ghana

A herpetofaunal survey of Muni-Pomadze Lagoon, during the main rainy season (May–June), recorded a total of 32 species (13 amphibians and 19 reptiles). Three species are the first records for coastal habitats in Ghana: Kinixys homeana, Calabaria reinhardti, and Bothrophthalmus lineatus. None of the surveyed species are restricted to Ghana. The most diverse herpetofaunal community occurs in grassland thicket, with 26 species (81% of the sampled herpetofauna). Freshwater ponds include 12 species, while only three species (all amphibians) occur in brackish lagoons. Herpetofaunal conservation efforts at these sites should focus on protecting and monitoring grassland coastal thicket and freshwater ponds. Currently, freshwater pond habitats appear to be stable, but coastal thicket is being lost to provide new agricultural land at Muni. Hyperolius reedfrogs, pythons (Python regius) and monitor lizards (Varanus exanthematicus and V. niloticus) appear to offer the greatest potential for undertaking long-term monitoring of the coastal lagoon herpetofauna, because they can be more readily surveyed, and are likely to be sensitive to a broad range of environmental stressors.     

Diet of Zonocerus variegatus (Linné, 1758) (Orth., Acrididae) in cassava fields in Bénin

Abstract:  This paper presents the results of a study on the diet of Zonocerus variegatus in cassava agro-ecosystems at Allada, south Benin. The diet was determined by the analysis of plant fragments in the faeces of insects sampled in the fields. The grasshoppers studied consumed 21 plant species among the 81 found in the fields. Cassava, maize, Mallotus oppositifolius and Chromolaena odorata were the major food plants for Z. variegatus in this system. The presence of Z. variegatus in different fields was observed depending on the season and the presence of certain plant species. There was no relationship between plant frequency in the diet and in the field. Cassava was the preferred food resource for mature nymphs and adults. During the dry season, young nymphs stayed near the hatching sites and where good food resources were available. At this time, the grasshoppers were present in a field where cassava was not abundant but where maize and weeds were available. During the dry season, Z. variegatus had a broader diet than during the wet season. This contradicts the current hypothesis that the water content of plants and the floral diversity determines food preference. The dry season is also the time when C. odorata leaves were found in the faeces of both adults and nymphs. These observations made in West Africa are similar to those made in Central Africa, particularly for the number of plant species found in the faeces, 21 (26% of all plant species found in the fields) in Bénin and 17 (23%) in the Congo. The increase of the sample size and the great differences between the ecoregional situation of the study sites do not substantially change the number of plant species included in the diets. In the area covered by this study, C. odorata is not the major substitute for cassava during the dry season, although it remains a major food source and an especially visible food resource.     

Correlates of active body temperatures and microhabitat occupation in nine species of central Australian agamid lizards

Body temperatures of active lizards and their correspondence with microhabitat occupation were studied for nine species of agamid lizards in the central Australian arid zone. Thermoregulatory behaviour was also documented using several measures, such as the use of shade and perch height. The effects of thermal environment on lizard habitat occupation were hypothesized to be significant, because desert regions experience daily and seasonal extremes of temperature that are well in excess of a lizard’s preferred temperature range. All species, except Ctenophorus isolepis and Diporiphora winneckei, were found to have body temperatures that corresponded closely to ground and surface temperatures. Thermoregulatory behaviour was also found to be important throughout a lizard’s daily activity; all study species, other than Ctenophorus isolepis, were found to increase their perch height in the middle of the day. Ctenophorus isolepis was shown to be a strictly terrestrial species that uses the shade of spinifex in its thermoregulatory behaviour. Species exhibited a non‐random selection of microhabitats and a preference for a particular set of thermal and structural factors. In this study, it was shown that structural factors were particularly important in microhabitat occupation. Thermal factors accounted for a smaller proportion of variance in microhabitat occupation, but still played a considerable role in the microhabitat use in central Australian agamids.     

Life history studies of anisocentropus kirramus neboiss (trichoptera: Calamoceratidae) in a tropical Australian rainforest stream

Eggs and larvae of Anisocentropus kirramus were collected from leaf packs in riffles and pools in a small upland rainforest stream in tropical Queensland. Adults were collected in floating emergence traps. Egg masses contained 80–100 eggs. None developed in water at 12–15°C but at 22–25°C larvae hatched in 3–10 days. There were five larval instars and complete development appeared to take several months. Instars II‐V were present in all nine months sampled; instar I was present in all but one month. Adults emerged in all ten months sampled, but there was clear seasonality with peak emergence in the summer. The sex ratio of adults was 1:1.