Variation in the effect of profitability on prey size selection by the lacertid lizard Psammodromus algirus

Maximizing the average rate of energy intake (profitability) may not always be the optimal foraging strategy for ectotherms with relatively low energy requirements. To test this hypothesis, we studied the feeding behaviour of captive insectivorous lizards Psammodromus algirus, and we obtained experimental estimates of prey mass, handling time, profitability, and attack distance for several types of prey. Handling time increased linearly with prey mass and differed significantly among prey types when prey size differences were controlled for, and mean profitabilities differed among prey taxa, but profitability was independent of prey size. The attack distance increased with prey length and with the mobility of prey, but it was unrelated to profitability. Thus, lizards did not seem to take account of the rate of energy intake per second as a proximate cue eliciting predatory behavior. This information was combined with pitfall-trap censuses of prey (in late April, mid-June and late July) that allowed us to compare the mass of the prey captured in the environment with that of the arthropods found in the stomachs of sacrificed free-living lizards. In April, when food abundance was low and lizards were reproducing, profitability had a pronounced effect on size selection and lizards selected prey larger than average from all taxa except the least profitable ones. As the active season progressed, and with a higher availability of food, the number of prey per stomach decreased and their mean ize increased. The effect of profitability on size selection decreased (June) and eventually vanished (July–August). This variation is probably related to seasonal changes in the ecology of lizards, e.g. time minimization in the breeding season as a means of saving time for nonforaging activities versus movement minimization by selecting fewer (but larger) prey in the postbreeding season. Thus, the hypothesis that maximizing profitability could be just an optional strategy for a terrestrial ectothermic vertebrate was supported by our data.     

Effect of Group Size on Time Budgets of Sichuan Snub-Nosed Monkeys (Rhinopithecus roxellana) in Shennongjia National Nature Reserve, China

Group size influences intragroup scramble competition, which in turn influences time budgets in some primates, and may impact age–sex classes differently. There is a great deal of debate about whether folivorous primates, e.g., colobines, experience significant feeding competition. Unlike most colobines, Sichuan snub-nosed monkeys (Rhinopithecus roxellana) live in extraordinarily large groups and eat mainly lichens supplemented by seasonal plant food. We examined the effect of group size on time budgets in this species by studying two groups of different sizes in the same habitat in Shennongjia National Nature Reserve, China (study periods: August 2006–July 2008 for the larger group, November 2008–July 2009 for the smaller group). Results showed that the distribution of activities throughout the day did not differ between groups, but that time budgets did differ. Specifically, the monkeys spent more time moving and less time resting in the larger group than in the smaller group. Intergroup comparisons for each age–sex class indicated that adult females (but not adult males or juveniles) in the larger group spent more time moving and less time resting, and tended to spend more time feeding compared to those in the smaller group. The results suggested that increased scramble competition was occurring for adult females in the larger group. We provided preliminary evidence for the existence of intragroup scramble competition in Rhinopithecus roxellana.     

Prey availability affects territory size,but not territorial display behavior,in green anole lizards

The availability of food resources can affect the size and shape of territories, as well as the behaviors used to defend territories, in a variety of animal taxa. However, individuals within a population may respond differently to variation in food availability if the benefits of territoriality vary among those individuals. For example, benefits to territoriality may differ for animals of differing sizes, because larger individuals may require greater territory size to acquire required resources, or territorial behavior may differ between the sexes if males and females defend different resources in their territories. In this study, we tested whether arthropod abundance and biomass were associated with natural variation in territory size and defense in insectivorous green anole lizards, Anolis carolinensis. Our results showed that both male and female lizards had smaller territories in a habitat with greater prey biomass than lizards in habitats with less available prey, but the rates of aggressive behaviors used to defend territories did not differ among these habitats. Further, we did not find a relationship between body size and territory size, and the sexes did not differ in their relationships between food availability and territory size or behavioral defense. Together, these results suggest that differences in food availability influenced male and female territorial strategies similarly, and that territory size may be more strongly associated with variation in food resources than social display behavior. Thus, anole investment in the behavioral defense of a territory may not vary with territory quality.     

An intraspecific analysis of trade-offs in sprinting performance in a West Indian lizard species (Anolis lineatopus)

We examined whether a trade-off exists in sprinting ability among individuals within the Caribbean lizard Anolis lineatopus. Specifically, we made the following predictions: Longer-legged (relative to body size) individual lizards should sprint faster than shorter-legged lizards on a broad (5.1 cm diameter) rod. However, longer-legged lizards should also decline in sprinting performance to a greater extent than shorter-legged lizards when sprinting on rods of different diameters. To test these predictions, we examined morphology and sprinting performance in adult male, adult female and juvenile A. lineatopus. As predicted, longer-legged lizards are faster sprinters than shorter-legged lizards on the broad substrate, but they also decline more in speed between the broad and narrow (0.7 cm diameter) dowel. However, despite statistically significant morphological differences among intraspecific classes, differences in morphology did not result in differences in sprinting performance among intraspecific classes, with the exception that larger lizards run faster than smaller lizards on each dowel size.     

One Solution for Two Challenges: The Lizard Microlophus atacamensis Avoids Overheating by Foraging in Intertidal Shores

In lizards, one of the most important behavioral mechanisms to cope with spatial and temporal variations in thermal resources observed is activity time. The longer a lizard can maintain activity, the more time it has to forage and reach larger adult body size. We studied the behavioral adjustments to different climatic regimens on daily and seasonal scales in three natural populations of the lizard Microlophus atacamensis along a latitudinal temperature and rainfall gradient. We also used Niche Mapper to determinate the amount of thermally suitable time for activity for this species. Abundance and daily activity patterns varied greatly over the year for the three populations. In summer and spring, the daily activity times were greater, and were reduced in fall and winter seasons. In summer, when stressful heat loads should prohibit activity over a midday gap, lizards did not show bimodal patterns of activity. Instead, they move to the cooler intertidal habitat. Abundance and thermal quality in the southernmost coolest site was lower, and the potential annual activity time decreases with latitude. Contrary to expectations, lizards from this locality showed the largest body sizes possibly due to diet and/or time to sexual maturation. Our results indicate that the intertidal habitat is a key factor that influences daily and seasonal activity of M. atacamensis lizards. While this habitat is not climatically optimal for lizards, it allows them to behaviorally extend their activity window and gain access to food in the intertidal areas.     

Comparative ecology of Varanus in the Great Victoria Desert

Abstract The ecologies of seven desert species of monitor lizards (Varanus), which are very variable in size, are described and compared. Data are reported on abundance, anatomy, behaviour, body temperature relationships, daily activity patterns, diet, growth, habitat and microhabitat, prey size, reproduction, seasonal patterns of activity, sexual dimorphisms, and tracks. As many as six of the seven species occur together in sympatry at one study site. New results reported here are merged with extensive data collected over the past quarter of a century to provide a comprehensive and detailed overview of numerous aspects of the natural history and ecology of the seven species in the Great Victoria Desert. One species of pygmy monitor has evolved large clutch size for unknown reasons. A food web for 40 species of desert lizards is presented. Hutchinsonian ratios of head lengths (larger/smaller) are significantly greater in two observed assemblages of sympatric varanids than in a null model consisting of all possible pairs of species of all Australian varanids. Evolution of body size and the two adaptive radiations of Varanus in Australia are discussed.     

Correlations between lizard cranial shape and diet: a quantitative, phylogenetically informed analysis

Although the relationship between dietary and phenotypic specialization has been well documented for many vertebrate groups, it has been stated that few such general trends can be established for lizards. This is often thought to be due to the lack of dietary specialization in many lizards. For example, many species that are reported to be insectivorous may also consume a variety of plant materials, and the reverse is often true as well. In this study, we investigate whether a correlation exists between general cranial form and dietary niche in lizards. Additionally, we test previously proposed hypotheses suggesting that herbivorous lizards should be larger bodied than lizards with other diets. Our data indicate that lizards specializing in food items imposing different mechanical demands on the feeding system show clear patterns of morphological specialization in their cranial morphology. True herbivores (diet of fibrous and tough foliage) are clearly distinguished from omnivorous and carnivorous lizards by having taller skulls and shorter snouts, likely related to the need for high bite forces. This allows herbivores to mechanically reduce relatively less digestible foliage. Carnivores have relatively longer snouts and retroarticular processes, which may result in more efficient capture and processing of elusive prey. When analysed in an explicit phylogenetic context, only snout length and skull mass remained significantly different between dietary groups. The small number of differences in the phylogenetic analyses is likely the result of shared evolutionary history and the relative paucity of independent origins of herbivory and omnivory in our sample. Analyses of the relationship between diet and body size show that on average herbivores have a larger body size than carnivores, with omnivores intermediate between the two other dietary groups. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 433–466.     

Sexual differences in growth strategies of the wolf spider Hygrolycosa rubrofasciata

In invertebrates, the size at maturation is considered to be important for adult fitness. In the wolf spider Hygrolycosa rubrofasciata, however, it is only females that clearly benefit of larger size through augmented egg production, while male mating success is determined by display activity not related to size. Thus, we can expect conflicting growth patterns for the sexes. Additionally, populations differ greatly in adult size: individuals from dry habitats are smaller than those from wet habitats. To study the sexual differences in reaction norms of growth, we reared spiderlings from seven populations at two food levels under controlled laboratory conditions and compared size at sexual maturity. The shapes of reaction norms for adult size differed between the sexes. In females, the reaction norms were parallel, but individuals from dry habitats tended to grow larger at the given food levels. In males, there was a significant interaction between food level and population without any consistent differences between populations. Maturation time was a plastic character in both sexes with no genetic differences among populations. However, females on low food level matured later and significantly smaller in size than those on high food level. Males also matured later on low food level, but they were nearly of the same size as males that received more food. Female growth patterns reflected the strong selection for large size at maturity. However, the patterns for males were highly variable, which could be explained by the weak overall selection on male size, which means that any environmental factors can affect male growing patterns. This revised version was published online in November 2006 with corrections to the Cover Date.     

东方田鼠家群个体体重、攻击性及胆量对其扩散的影响

扩散作为动物适应生存环境的重要特征之一,受到自身生物学特征及环境等方面的制约。以家群形式生活和子代雄鼠扩散为主的东方田鼠,其成员个体是否因领地食物和空间资源竞争导致体重小、攻击性弱及胆小个体先行扩散。以新鲜马唐叶片构建三块密集均质的食物斑块,在食物斑块周边以透明玻璃设置观测箱,采用透明塑胶管连接三块食物斑块作为动物扩散的通道,构建东方田鼠扩散行为观测装置。将东方田鼠家群子代成员投放至带有自身家群气味的食物斑块,测定成员个体在食物斑块上的觅食行为序列过程和参数,以及向其他食物斑块扩散的行为过程和参数以及家群中先行扩散个体体重、攻击性及胆量占所有家群数的比率,检验成员个体的体重、攻击性及胆量对扩散的影响。结果发现,体重小、攻击性弱和胆小个体的觅食启动时间极显著地大于体重大、攻击性强和胆大个体的,但其先行扩散的比率却显著地大于体重大、攻击性强和胆大个体的;然而体重小、攻击性弱及胆小个体的扩散开始时间显著或极显著地大于体重大、攻击性强及胆大个体的。结果揭示,东方田鼠家群成员随着年龄的增长和对食物及空间资源竞争的加剧,体重大、攻击性强及胆大个体会迫使体重小、攻击性弱及胆小个体先行扩散。     

The effect of body size on the thermoregulation of lizards on hot,dry Mediterranean islands

Body size shapes the overall biology of organisms. We assessed the impact of size on temperature regulation in populations of normal-sized and large-bodied insular Mediterranean lizards (Podarcis gaigeae, Lacertidae). We hypothesized that large lizards would achieve higher body temperatures and thermoregulate more effectively than their smaller kin. Large- and small-bodied lizards share the same thermoregulation pattern, achieving similar body temperatures in the field. Large lizards, however, prefer higher set-point temperatures. Lizards in both populations thermoregulate effectively, but large lizards thermoregulated less effectively than normal-sized lizards. The particular conditions at the islet that harbors the large-bodied population (harsh intraspecific competition) seem to account for this pattern.     

Ranging Patterns of Two Syntopic Howler Monkey Species (Alouatta guariba and A. caraya) in Northeastern Argentina

To avoid competition, ecologically similar and closely related species tend to differ in their patterns of habitat use when they live in sympatry. We compared ranging patterns of brown howler (Alouatta guariba) and black and gold howler (A. caraya) monkeys living syntopically, i.e., co-occurring and overlapping their ranges in the same habitat within the zone of sympatry, in the Atlantic Forest of northeastern Argentina with the objective of evaluating whether their use of space contributes to the avoidance of interspecific competition for food resources. During 12 mo we collected data on the ranging behavior of 2 groups of each howler species. We analyzed annual and seasonal daily path lengths and movement rates, home range size, use and overlap, habitat and vertical strata use, and intergroup encounters. Black and gold howlers traveled farther and faster during the time of relative food abundance (abundant season) than during the time of relative food shortage (lean season), and their movement rates were affected by group identity and increased with the proportion of fruits in the diet. Brown howlers’ traveling patterns were not affected by any of these factors. Home ranges for both species (95% fixed kernel; brown howlers: 31–70 ha, black-and-gold howlers: 17–112 ha) were among the largest recorded for Alouatta. For both species, core areas (50% fixed kernel) were larger for larger versus smaller groups, and decreased in the lean season compared to the abundant season. Both species showed similar patterns of habitat use, except for a slight vertical stratification. Groups of different species overlapped their ranging areas consistently more and responded to one another less aggressively during encounters than groups of the same species, suggesting that interspecific spatial niche separation for these two syntopic species is not occurring. The vertical stratification, as well as a day-to-day avoidance strategy, may be the only responses of species to one another that could reduce the potentially high levels of competition for food suggested by their elevated trophic niche overlap. A high degree of niche overlap may explain the parapatric distribution of howlers and other closely related and ecologically similar species of primates.     

Patterns of occurrence of corticolous myxomycetes on white oak trees of two different size classes

Data were obtained on the assemblages of corticolous myxomycetes (plasmodial slime moulds or myxogastrids) associated with the bark surface of living white oak (Quercus alba) trees from two different size classes. Bark samples obtained from larger trees were characterized by higher values for both species richness and diversity when compared to those collected from smaller trees. This might have been expected since the former possess a larger surface area and presumably have persisted over a longer period of time. However, the myxomycete assemblage associated with smaller trees was appreciably different and did not simply represent a depauperate version of the assemblage associated with larger trees. This suggests that the differences observed between size classes cannot be simply attributed to size alone.     

Evidence of Niche Partitioning under Ontogenetic Influences among Three Morphologically Similar Siluriformes in Small Subtropical Streams

Ontogenetic influences in patterns of niche breadth and feeding overlap were investigated in three species of Siluriformes (Heptapterus sp., Rhamdia quelen and Trichomycterus poikilos) aiming at understanding the species coexistence. Samplings were conducted bimonthly by electrofishing technique from June/2012 to June/2013 in ten streams of the northwestern state of Rio Grande do Sul, Brazil. The stomach contents of 1,948 individuals were analyzed by volumetric method, with 59 food items identified. In general Heptapterus sp. consumed a high proportion of Aegla sp., terrestrial plant remains and Megaloptera; R. quelen consumed fish, and Oligochaeta, followed by Aegla sp.; while the diet of T. poikilos was based on Simuliidae, Ephemeroptera and Trichoptera. Specie segregation was observed in the NMDS. Through PERMANOVA analysis feeding differences among species, and between a combination of species plus size classes were observed. IndVal showed which items were indicators of these differences. Niche breadth values were high for all species. The niche breadth values were low only for the larger size of R. quelen and Heptapterus sp. while T. poikilos values were more similar. Overall the species were a low feeding overlap values. The higher frequency of high feeding overlap was observed for interaction between Heptapterus sp. and T. poikilos. The null model confirmed the niche partitioning between the species. The higher frequency of high and intermediate feeding overlap values were reported to smaller size classes. The null model showed resource sharing between the species/size class. Therefore, overall species showed a resource partitioning because of the use of occasional items. However, these species share resources mainly in the early ontogenetic stages until the emphasized change of morphological characteristics leading to trophic niche expansion and the apparent segregation observed.     

Early Activity Rates do not Predict Growth and Future Body Size of Juvenile Eastern Fence Lizards,Sceloporus undulatus

Selection favors larger body size in many taxa. In some species, larger individuals are more active and bolder than smaller conspecifics, but the nature of this relationship is unclear: Is body size a predictor or a consequence of behavior? Any effect of behavior on body size may be through its effect on competitive ability, suggesting that the presence of potential competitors could exaggerate or suppress this relationship. In this study, we tested whether an individual's activity rates early in life predict its future body size by measuring same‐aged, sibling eastern fence lizards before (8 d) and after (8 wk) they significantly diverged in body size. We tested for an effect of conspecific presence (potential competition) on the relationship between early behavior and future body size by housing some lizards in sibling groups and others individually, using a split‐clutch design. Our results reveal that individuals' activity rates do not significantly differ between 8 d and 8 wk of age. At 8 wk (but not 8 d) of age, more active siblings were also larger in both housing treatments; however, early activity rates did not predict body size later in development for either of these groups. Conversely, body size at hatching did predict size at 8 wk. Although variation in activity rates exists prior to divergence in body size, and activity and body size are correlated later in development, our results suggest that higher activity rates are unlikely to be driving body size divergence in this species. Instead, very small differences in body size at hatching appear to be compounded over time and drive much more exaggerated differences in later body size.     

Reproductive Success and Body Size in the Cricket Gryllus firmus

Male body size influences mate choice and sexual selection in many animal species. Here we investigate the role of male body size in the reproductive success of the field cricket Gryllus firmus. This species hybridizes with a close smaller relative, G. pennsylvanicus, and it is thought that this size difference may affect reproductive isolation between these species. We paired large and small G. firmus males with a single G. firmus female and genotyped the resulting offspring. Overall, larger males sired a greater proportion of offspring and in a majority of the crosses the larger male sired all of the offspring. For crosses in which both males sired offspring, there was no difference in the proportion of offspring sired by small and large males. Intrasexual competition, female choice, and differences in ejaculates between males could all influence the patterns we observe. We discuss the implications of our findings within the context of reproductive isolation between G. firmus and G. pennsylvanicus.     

Phenotypic sorting in morphology and reproductive investment among sociable weaver colonies

Colony sizes in birds can vary by orders of magnitude within species, and many studies have shown that selection pressures differ dramatically among small and large colonies. Does such selection result in phenotypic sorting at the level of individuals? This study describes inter-colony differences in morphology and reproductive investment in a population of a highly colonial, communal and sedentary African passerine bird, the sociable weaver Philetairus socius. Relative colony sizes were fairly stable over a 10-year period. Adults differed among colonies in terms of bill morphology, condition, body size and degree of ectoparasite infestation, and the last two declined consistently with colony size. In larger colonies, smaller eggs were laid, and nestlings were more parasite-infested, showed weaker cell-mediated immune responses, and experienced higher levels of brood reduction and snake predation. Taken together with another study showing that adult survival is higher in larger colonies, these results suggest that patterns of age-specific mortality are consistently related to colony size in the sociable weaver. Based on these observations I suggest two hypotheses that might account for the observed phenotypic sorting, involving colony size-dependent patterns in (1) density-dependent competition for food and (2) adaptive life-history adjustment.     

云南拉沙山黑白仰鼻猴群体规模对冬春季日移动距离和活动时间分配的影响

生态限制模型(Ecological constraints model)认为随种群规模增加,灵长类种群会增加日移动距离、移动时间和取食时间,减少休息时间.果食性灵长类为取食斑块分布的高质量食物资源(如果实)而存在群内分摊竞争(Within-group scramble competition),很好地验证了生态限制模型...     

Contrasting responses of two passerine bird species to moose browsing

Large herbivores may modify the ecosystem in a way that affects habitat quality and resource availability for other fauna. The increase in wild ungulate abundance in many areas may therefore lead to ecosystem changes, affecting distribution and reproduction of other species. Moose (Alces alces) in Scandinavia is a good example of a herbivore that has recently increased in abundance and has the potential to affect the ecosystem. In this study, we investigated how different levels of moose winter activity around supplementary feeding stations for moose affect reproduction in two insectivorous passerines: great tits (Parus major) and pied flycatchers (Ficedula hypoleuca). The two bird species showed contrasting responses to high moose activity at feeding stations. Great tits avoided habitats with high moose activity, where fledging success and feeding frequency was lower than at low moose activity habitats. Flycatchers nested more often at high moose activity habitats where fledging weight and feeding frequency were higher than at low moose activity habitats. Filming of nest boxes with great tits showed an increase in adult Lepidoptera in the diet at supplementary feeding stations for moose, and a smaller size of caterpillar prey at intermediate moose activity. The results support the hypothesis that herbivores may affect insectivorous passerines through changed arthropod food availability.     

Pattern of space use by female black bears in the White River National Wildlife Refuge,Arkansas, USA

The manner in which space is used by animals may influence several aspects of biology, including the pattern of resource use and intra-specific competition. We monitored 16 radio-collared female black bears (Ursus americanus) for 9,216 radio days during 1993–1995 in the White River National Wildlife Refuge (WRNWR), Arkansas, U.S.A. to investigate space use patterns. Annual home ranges (95% convex polygon) ranged from 2.10 to 11.34 km² with a mean (± SD) size of 4.90 (± 2.09) km² (n = 16). Largest home ranges were occupied by 2 females with yearlings during one year of study. Home ranges among neighbouring bears overlapped considerably. Although bears maintained larger home ranges during summer, the size of home range did not differ among seasons (P > 0.50). Our estimates of home range size for female black bears were smaller than those obtained in a study of the same population during 1979–1982. Because the size of the bear population at WRNWR was substantially smaller (about 130 bears) during 1979–1982 compared to the present population of ≥348 bears, these results suggested that population density and size of female black bear home ranges may be negatively correlated. Conservation implications of density-dependent space use pattern are also discussed.     

Anthropogenically modified habitats favor bigger and bolder lizards

Anthropogenic activities often create distinctive but discontinuously distributed habitat patches with abundant food but high risk of predation. Such sites can be most effectively utilized by individuals with specific behaviors and morphologies. Thus, a widespread species that contains a diversity of sizes and behavioral types may be pre‐adapted to exploiting such hotspots. In eastern Australia, the giant (to >2 m) lizard Varanus varius (lace monitor) utilizes both disturbed (campground) and undisturbed (bushland) habitats. Our surveys of 27 sites show that lizards found in campgrounds tended to be larger and bolder than those in adjacent bushland. This divergence became even more marked after the arrival of a toxic invasive species (the cane toad, Rhinella marina) caused high mortality in larger and bolder lizards. Some of the behavioral divergences between campground and bushland lizards may be secondary consequences of differences in body size, but other habitat‐associated divergences in behavior are due to habituation and/or nonrandom mortality.