Importance Of Body Size Research Articles

Small workers are more persistent when providing and requiring help in a monomorphic ant

The common sand-dwelling Formica cinerea ants possess monomorphic workers, yet with considerable and easily identified size variation. Considering the importance of body size in polymorphic ants and other animals, we test whether size-dependent differences in behaviour occur in this species. We focus on the behaviour of large and small foragers in the context of rescue occurring between nestmates when one of them is entrapped and requires help. We show that workers of different sizes are characterized by a similar frequency of rescue activity and time delay to the first act of rescue. However, small workers rescue for longer than large workers. These results indicate that, although there is no size-related rescue specialization in F. cinerea foragers, small rescuers behave differently than large ones in terms of rescue persistence. Additionally, we show that small workers are more active when trapped. We suggest that variation in behavioural persistence of differently-sized workers may increase the efficiency of rescue actions. This study is the first to find a connection between body size and rescue behaviour in ants and the first to quantify and analyze the behaviour of individuals in need of rescue. These findings add substantially to our understanding of social insects and, more generally, highlight the need to study among-individual behavioural variation in social animals, including those in which body size is judged minute and irrelevant.

Male mate choice in mosquitofish: personality outweighs body size

BackgroundDespite its important implications in behavioural and evolutionary ecology, male mate choice has been poorly studied, and the relative contribution of personality and morphological traits remains largely unknown. We used standard two-choice mating trials to explore whether two personality traits (i.e., shyness and activity) and/or body size of both sexes affect mate choice in male mosquitofish Gambusia affinis. In the first set of trials involving 40 males, we tested whether males would prefer larger females and whether the preference would be affected by males’ body length and personality traits, and females’ activity level. In the second set of trials (using another 40 males), we tested whether males would prefer more active females and whether the preference would be affected by males’ body length and personality traits.ResultsBoth shyness and activity in males were significantly repeatable and constituted a behavioural syndrome. No overall directional preference for large (or small) females with the same activity levels was detected because larger males preferred larger females and smaller males chose smaller females. Males’ strength of preference for larger females was also positively correlated with the activity level of larger females but negatively with the activity level of smaller females. Males spent more time associating with active females regardless of their body lengths, indicating males’ selection was more influenced by female activity level than body size. Males’ preference for inactive females was enhanced when females became active. There was no convincing evidence for the effect of males’ personality traits or body length on their preferences for females’ activity level.ConclusionsOur study supports the importance of body size in male mate choice but highlights that personality traits may outweigh body size preferences when males choose mating partners.

Noctuid and geometrid moth assemblages show divergent elevational gradients in body size and color lightness

Previous macroecological studies have suggested that larger and darker insects are favored in cold environments and that the importance of body size and color for the absorption of solar radiation is not limited to diurnal insects. However, whether these effects hold true for local communities and are consistent across taxonomic groups and sampling years remains unexplored. This study examined the variations in body size and color lightness of the two major families of nocturnal moths, Geometridae and Noctuidae, along an elevational gradient of 700 m in Southern Germany. An assemblage‐based analysis was performed using community‐weighted means and a fourth‐corner analysis to test for variations in color and body size among communities as a function of elevation. This was followed by a species‐level analysis to test whether species occurrence and abundance along an elevation gradient were related to these traits, after controlling for host plant availability. In both 2007 and 2016, noctuid moth assemblages became larger and darker with increasing elevation, whereas geometrids showed an opposite trend in terms of color lightness and no clear trend in body size. In single species models, the abundance of geometrids, but not of noctuids, was driven by habitat availability. In turn, the abundance of dark‐colored noctuids, but not geometrids increased with elevation. While body size and color lightness affect insect physiology and the ability to cope with harsh conditions, divergent trait–environment relationships between both families underline that findings of coarse‐scale studies are not necessarily transferable to finer scales. Local abundance and occurrence of noctuids are shaped by morphological traits, whereas that of geometrids are rather shaped by local habitat availability, which can modify their trait–environment‐relationship. We discuss potential explanations such as taxon‐specific flight characteristics and the effect of microclimatic conditions.

Birthweight, Childhood Body Mass Index, Height and Growth, and Risk of Polycystic Ovary Syndrome

Introduction: Adult obesity is linked with polycystic ovary syndrome (PCOS), but the importance of body size at ages before PCOS is diagnosed is unknown. Objective: To investigate associations between a woman’s own birthweight, childhood body mass index (BMI), height and growth patterns in relation to her risk of PCOS. Methods: We included 65,665 girls from the Copenhagen School Health Records Register, born in the period 1960–1996, with information on birthweight and measured weight and height at the ages of 7–13 years. Overweight was defined using International Obesity Task Force (IOTF) criteria. From the Danish National Patient Register, 606 women aged 15–50 years were identified. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated by Cox regression analysis. Results: Birthweight was not associated with PCOS. At the age of 7–13 years, girls with overweight had a higher risk of developing PCOS than girls without overweight; HR 2.83 (95% CI 2.34–3.42) at age 7 years and 2.99 (95% CI 2.38–3.76) at age 13 years. Furthermore, girls with overweight at both 7 and 13 years had a higher risk of developing PCOS than girls without overweight or overweight at only one age. Height was positively associated with PCOS risk at all ages. Girls who were persistently tall or changed from tall to average height had a higher risk of developing PCOS than girls with average height growth. Conclusion: Overweight and tall stature in childhood are positively associated with PCOS risk, but birthweight is not.

Museum Specimens Reveal Life History Characteristics in Plethodon montanus

Amphibian life history strategies can vary across broad geographic patterns, which have been explained, at least in part, by how development, growth, maintenance, and reproduction respond to temperature. However, there is a dearth of information regarding life history traits and their variation among populations for many amphibian species, which prevents assessment of these broad patterns among species. Therefore, we used museum specimens to assess the variation in reproductive condition of Plethodon montanus across its range and used skeletochronology at five populations along an elevational gradient to determine the elevational variation in age, growth rate, and asymptotic size. We found that body size and temperature seasonality best explained the variation in the presence of eggs and a mental gland, whereas body size alone best explained the presence of enlarged pigmented testes. We also found that longevity in P. montanus is at least 12 years with higher elevations having a higher proportion of older individuals compared to lower elevations and that size was a better explanation of reproductive condition than age across the elevation. Our results further demonstrate the importance of body size for amphibian life history traits and the utility of museum specimens to estimate these traits. Variation in reproductive condition across the range of P. montanus is likely the result of variation in growing season length. Lastly, we found evidence suggesting asymptotic size and growth rates may have changed over the last half century, which would ultimately affect fertility and other life history traits and warrants future studies.

Comparative analysis of feeding habits and dietary niche breadth in skates: the importance of body size, snout length, and depth

Skates (Elasmobranchii, Rajiformes) are a morphologically conservative group of bentophagous chondrichthyan fishes with a high degree of endemism, that occur on marine soft bottoms. Subtle morphological aspects and bathymetric distribution are traits that vary among skate species that could have implications for their feeding ecology. We test how body size, snout length and bathymetric distribution influence the feeding habits and dietary niche breadth in skates using data on 71 species taken from the literature. We hypothesized that snout length has an effect on diet composition. We also hypothesized that dietary niche breadth increases with increasing depth range and decreases with increasing body size of skate species. Generalized additive models for location scale and shape were fitted with taxonomic level (genera nested within family) included as a random effect term in each model. A model selection approach to test the level of support for alternative models was applied. We found that skate species that forage on large prey have the largest body size and skate species with the smallest body size prey on small and medium-sized invertebrates. The results indicated that body size has an effect on feeding habits of skates, whereas an effect of snout length was not supported. Bathymetric variables have an effect on the diet of skates. Our prediction that dietary niche breadth increases with increasing depth range and decreases with increasing body size of skate species was supported in part: in a first phase the relationship between dietary niche breadth and body size is positive, then in a second phase, including species larger than 1000 mm total length, the relationship become negative.

In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 26:33-40 (2017) - DOI: https://doi.org/10.3354/ab00669 In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material R. C. Challener1,*, J. B. McClintock2 1Bellarmine University, Department of Biology, Louisville, KY 40205, USA 2University of Alabama at Birmingham, Department of Biology, Birmingham, AL 35294, USA *Corresponding author: rchallener@bellarmine.edu ABSTRACT: Righting behavior has been used extensively in laboratory studies of sea urchins as an indicator of stress under various environmental conditions. In situ measurements of the natural righting response of sea urchins would serve to place such laboratory measurements in an ecological context as well as potentially validate laboratory control conditions. We investigated the righting response of the sea urchin Lytechinus variegatus in seagrass and sand bottom habitats of Saint Joseph’s Bay, Florida. Field-measured righting times (other than the exception mentioned below) in L. variegatus were similar to those measured in laboratory studies. Moreover, as seen in multiple sea urchin species in laboratory studies, smaller individuals exhibited significantly shorter righting times than larger individuals. Importantly, sea urchins lacking covering material (shell material, seagrass blades) that were placed on open sand patches took significantly longer to right than those with covering material placed on sand patches. Our field observations indicate the importance of sea urchin size, substrate type, and the presence or absence of covering materials when making righting measurements in the laboratory or the field. Our findings also suggest that higher water velocities facilitate righting, as at higher flows on sand patches, the presence/absence of covering material no longer significantly impacted righting time. These findings are ecologically important as they indicate that, under certain natural conditions (sand substrate, low availability of covering materials and low water velocities), L. variegatus that are displaced onto their aboral side are more vulnerable to predation. KEY WORDS: Righting response · Covering behavior · Soft bottom · Echinodermata · Echinoidea Full text in pdf format PreviousNextCite this article as: Challener RC, McClintock JB (2017) In situ measurements of righting behavior in the common sea urchin Lytechinus variegatus: the importance of body size, substrate type, and covering material. Aquat Biol 26:33-40. https://doi.org/10.3354/ab00669 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 26. Online publication date: February 21, 2017 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2017 Inter-Research.

Effects of salinity on nest-building behaviour in a marine fish.

BackgroundParental allocation and reproductive success are often strongly influenced by environmental factors. In this respect, salinity is a key factor influencing species distributions and community structure in aquatic animals. Nevertheless, the effects of salinity on reproductive behaviours are not well known. Here, we used the sand goby (Pomatoschistus minutus), a small fish inhabiting a range of different salinities, to experimentally assess the effects of changes in salinity on nesting behaviour, a key component of reproduction in sand gobies and many other taxa.ResultsWe found that salinity levels influenced some aspects of male nesting behaviour (i.e. nest entrance size) but not others (i.e. latency to build a nest, choice of nest site, sand on top of nest) and that small and large individuals were differently affected. In particular, the importance of body size in adjustment of nest entrance depended on the salinity level.ConclusionThe results support the prediction that geographically widespread aquatic species, such as sand gobies, are able to perform well under a range of salinity levels. The phenotype by environment interaction found between male size and behavioural responses to salinity can, in turn, help to explain the notable variation observed in nest-building (and other) behaviours closely linked to reproduction.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0067-y) contains supplementary material, which is available to authorized users.

Size-assortative copulation in the simultaneously hermaphroditic pond snail Radix auricularia (Gastropoda: Pulmonata)

To better understand the importance of body size in hermaphroditic mating, we studied the mating behaviour of the pond snail Radix auricularia. This simultaneous hermaphrodite exhibits a positive correlation between body size and egg production and provides weak evidence for size-assortative mating. In addition to this mating pattern, the partner performing the male role was significantly smaller than the mounted partner, performing the female role. In this study, two laboratory experiments were done to test whether body size has (1) an effect on mate choice of the sperm donor, and (2) poses mechanical constraints. These snails did not display physical limitation in mating with a much larger or smaller partner. In the mate choice experiment, we found no evidence for significant preferences for large partners. Therefore, mate choice of sperm donor and mechanical constraints are not likely to contribute to the formation of size-assortatively mating pairs in this species, which contributes to understanding about how these processes work in hermaphrodites.

Consumer–plant interaction strength: importance of body size, density and metabolic biomass

Explaining variability in the strength and sign of trophic interactions between primary consumers and plants is a long‐standing research challenge. Consumer density and body size vary widely in space and time and are predicted to have interactive effects on consumer–plant interactions. In a southern US salt marsh, we used replicate field enclosures to orthogonally manipulate the body size (mass) and density of a dominant consumer (a snail). We investigated impacts (leaf damage and biomass) on monocultures of cordgrass, the foundation species, over three months. Increasing consumer density and body size increased leaf damage additively and, as predicted, multiplicatively reduced plant biomass. Notably, size and density determined the sign of consumer impact on plants: low to medium densities of small consumers enhanced, while high densities of large consumers strongly suppressed, plant biomass. Finally, total consumer metabolic biomass (mass0.75) within an enclosure parsimoniously explained plant biomass response, supporting theoretical predictions and suggesting that multiplicative effects of density and body size resulted from their effects on total metabolic biomass. The consequences of changes in consumer density and body size resulting from anthropogenic perturbations may therefore be predicted based on metabolic biomass.SynthesisConsumer size, density and biomass can all strongly affect consumer–plant interactions. Though density and body size have been extensively studied as drivers of variation in interaction strength, the role of biomass as the ultimate driver has been less appreciated. We manipulated body size and density of a single consumer species and, based on metabolic theory, integrated these into a single variable: total metabolic biomass. Our results suggest that changes in interaction strength attributed to size or density may in fact be due to changes in metabolic biomass. This metric could thus serve as a useful tool in further understanding species interactions.

Importance of body size and hunting strategy during interactions between the Mexican red-rump tarantula (Brachypelmavagans) and the wolf spiderLycosasubfusca

Behavioural adaptation helps animals to maximize their ability to obtain food and to avoid being eaten, increasing fitness. To achieve this, they must assess predation risk and evaluate foraging needs simultaneously. In two sympatric spider species, the wandering wolf spider Lycosa subfusca F.O.P. Cambridge, 1902 and the sit-and-wait Mexican red-rump tarantula (Brachypelma vagans Ausserer, 1875), we studied the relationship between predatory behaviour and antipredatory behaviour at different life stages. In the laboratory, encounters were organized between one wolf spider (small, medium-sized, or large) and one tarantula (spiderling, small, medium-sized, or large). Attack latencies and behaviours were recorded. The results showed that wolf spiders attacked and successfully captured younger tarantulas, while they avoided or retreated from older ones. Tarantulas preferentially attacked and captured older wolf spiders. On other hand, younger wolf spiders were more cautious than older ones, which waited until for the tarantulas to attack before retreating. Younger tarantulas were also more cautious than adults, which never retreated from attack and increased their success in attacks with age. Finally, we discuss the relationship between the predatory strategies of both spiders with their perception abilities and life history.

Marine biodiversity and ecosystem functioning: frameworks, methodologies, and integration

1. Marine biodiversity: its history, present status and future threats 2. Biodiversity in the context of ecosystem function 3. Ecosystem function and co-evolution of terminology in marine science and management 4. Ecological consequences of declining biodiversity: A biodiversity-ecosystem function (BEF) framework for marine systems 5. Lessons from the fossil record: the Ediacaran radiation, the Cambrian radiation, and the end-Permian mass extinction 6. The analysis of biodiversity-ecosystem function experiments: partitioning richness and density-dependent effects 7. The importance of body size, abundance, and food web structure for ecosystem functioning 8. Effects of biodiversity-environment conditions on the interpretation of biodiversity-function relations 9. Extending the approaches of biodiversity and ecosystem functioning to the deep ocean 10. Incorporating extinction risk and realistic biodiversity futures: Implementation of trait based extinction scenarios 11. Biodiversity and ecosystem functioning: an ecosystem-level approach 12. Multitrophic biodiversity and the responses of marine ecosystems to global change 13. Reality check: issues of scale and abstraction in biodiversity research, and potential solutions 14. Why bother going outside: the role of observational studies in understanding biodiversity-ecosystem function relationships 15. Implementing an ecosystem approach: predicting and safeguarding marine biodiversity futures Index

Spatial and seasonal variation in δ15N and δ13C values in a mesopredator shark, Squalus suckleyi, revealed through multitissue analyses

We used variance decomposition to explore the importance of body size, sex, location, and sampling period as predictors of intrapopulation variation in δ15N and δ13C values in spiny dogfish Squalus suckleyi from the Puget Sound–Strait of Georgia basin. Isotopes in two tissues with long (dorsal white muscle) and short (liver) isotopic turnover rates (~1 year and ~3–4 months, respectively) were sampled to evaluate whether the relative importance of each variable differed depending on the time span over which diet information was integrated. Significant spatial variation was observed in both muscle and liver isotopic composition, whereby location uniquely explained 25 and 17 % of the total variance, respectively. The remaining variables explained considerably less variation in both tissue types. Furthermore, evidence of seasonal isotopic shifts in δ15N and δ13C values was apparent, but differed widely in direction and magnitude among groups. These findings suggest that members of spiny dogfish schools may share a common feeding history, possibly by spending extended time periods (weeks to months) foraging in a spatially fixed region. Another explanation is that individuals may move and feed in aggregations that exist for extended periods. These complex group-level patterns suggest that even for large-bodied, motile predators such as sharks, population-level diet estimates derived from averaging isotope ratios of individuals collected from only a few locations may poorly reflect the true population mean.

Advancing Frontiers, with a retrospective

editorial ISSN 1948‐6596 Advancing Frontiers, with a retrospective The first issue of a new volume of Frontiers of Bio‐ geography, following soon after a Biennial meet‐ ing of the International Biogeography Society (IBS), provides a timely opportunity to take stock of achievements and to chart the new course for the journal. We aim to do this in two installments: first a brief retrospective herein, followed by a prospective in the next issue. Frontiers of Biogeography is now seven is‐ sues, and not quite two years, old (the first issue was published in September 2009). During this period, we have maintained an average of over 30 pages per issue of diverse content, including opin‐ ions and perspectives, book reviews, news and comment on the current literature, and updates for the IBS membership. That level of output, al‐ though small by the standards of an established journal, is a testament to the support of IBS mem‐ bers in submitting articles and a dedicated edito‐ rial team. We take this opportunity to thank this team of editors, who are listed inside the cover of all the issues of the journal. Many of them are early‐career scientists with a great enthusiasm for our subject: key members of the next generation of leading biogeographers. It is great to have such dynamic, motivated people involved. A key part of our mission is inherited from the antecedent IBS Newsletter: to abet communi‐ cation among all the members of IBS. The mem‐ bership corner remains a pillar of that mission, in partnership with the IBS blog, facebook, and twit‐ ter sites. We have been able to bring some of the latest content from the diverse biogeography lit‐ erature to your laptop, including discussion of top‐ ics in the peer‐reviewed literature. With the Wiley –Blackwell biogeography journals discontinuing their book reviews about four years ago, Frontiers is now the place to look for reviews of, and infor‐ mation about, books in our field; the recent ap‐ pointment of Markus Eichhorn as Book Reviews Editor has made this a strong feature of the jour‐ nal. We also bring early delivery of ideas gestating within the minds of a series of highly regarded interviewees; the interview with Robert E. Ricklefs in this issue brings up to date the series on Alfred Russel Wallace Award winners. In this vein, the current issue again engages with some of the very latest in biogeography in a series of reports from the 5 th Biennial Interna‐ tional Conference of the IBS, convened in Herak‐ lion, Crete. Each report provides a summary of cutting‐edge topics within the field, but we sug‐ gest there are gems hidden in these reports that emerge most clearly when reading the entire is‐ sue’s contents in quick succession, regardless of speciality. Several common themes spring out. To choose just two examples, the importance of body size (see the summaries of the Two Lenses, Hot Topics, and Marine Biogeography symposia) and the role of ecology in species distributions (Two Lenses and Marine Biogeography symposia) have a large presence across nominally distant disci‐ plines. Additionally, the Conservation Biology and Palaeoecology summaries explicitly draw links between symposia. These glimpses of transversal‐ ity are evidence that, by bringing together bio‐ geographers from different areas of research, the IBS meetings are facilitating a multidisciplinary exchange from which conceptual syntheses can emerge. But also, reading the book reviews and interview, we are led to consider the merits of practising biogeography in different ways: focus‐ ing on place, question or taxon, using shallow sampling with great breadth or sampling intensely with depth. In this issue we have the added op‐ portunity of viewing one symposium through the eyes of both the organizers and two student at‐ tendees (fittingly, this is the Two Lenses sympo‐ sium on biogeography and ecology). The diversity of points of view, conceptual and methodological approaches and research topics provided by these discussions, in print, represents the vitality of the meeting, the society and the discipline they seek to represent. Thus, as IBS continues to establish itself as a scientific society, Frontiers of Biogeography also is evolving to take on a broader role in communicat‐ ing biogeography. Our long‐standing series of con‐ tributed opinion and perspective articles (now highlighted on the Frontiers of Biogeography frontiers of biogeography 3.1, 2011 — © 2011 the authors; journal compilation © 2011 The International Biogeography Society

Size is not everything: a meta-analysis of geographic variation in microscopic eukaryotes

Aim To analyse how important body size is for geographic variation in microscopic organisms in the marine environment and thereby determine the validity of the ‘everything is everywhere’ hypothesis. Location Marine environments, globally. Methods Studies on geographic variation in all marine eukaryotes smaller than 1 mm and all marine copepods were compiled from the literature and incorporated in multiple binomial regressions to analyse the effect of body size, lifestyle, environmental isolation and taxonomic affinity on the probability of different regions being reciprocally monophyletic. Sample size was also analysed, because a negative relationship between sample size and probability of being reciprocally monophyletic would indicate biases due to undersampling in the original studies. Separate analyses were performed for three potential types of barriers to gene flow for marine organisms (the water barrier of the middle of the oceans, the temperature barrier of the equator, and the land barrier of the continents). Results Environmental isolation was the only variable in the best-fitting model for the probability of populations from each side of an ocean being reciprocally monophyletic. The estimated importance of body size was quite large and the lack of this variable in the best-fitting model may be a power issue due to the small sample size (n= 40). Both environmental isolation and body size were important for the probability of monophyletic populations in different hemispheres. The analysis of isolation between different oceans did not produce clear results. The relationship between sample intensity and probability of being reciprocally monophyletic was positive for the isolation between different oceans and non-existent for the two other analyses. Main conclusions The results showed that body size was an important factor governing the potential for geographic variation but not the only important factor by far. These results clearly weaken the ‘everything is everywhere’ hypothesis as they showed that microscopic organisms may have geographic variation, albeit to a lesser degree than larger organisms.

Fecundity in the hermaphroditic land snail Succinea putris (Pulmonata: Succineidae): does body size matter?

The relative importance of body size as a factor in life-history variation is poorly understood in hermaphrodites, especially in reciprocally mating species. Succinea putris is a reciprocally mating land snail with different courtship roles, i.e. an ‘active’ individual mounts the shell of a ‘passive’ partner after which penes are intromitted simultaneously. This species was used to examine (1) the relation between individual body size and fecundity; (2) whether an individual’s body size affects fecundity of the partner; (3) the relation between courtship role and fecundity; and (4) the relation between clutch size and egg weight under laboratory conditions. Simultaneously, we studied growth rate, hatching success and time budgets, as these may co-vary with fecundity. First, highly significant correlations between an individual’s body size and its fecundity and between an individual’s body size and the onset of egg laying were found. These effects were influenced by the relative size of the two partners in a mating pair and the effects on fecundity were observed only in passive (not active) individuals. Second, larger individuals laid heavier eggs. Third, active and passive individuals did not differ in fecundity, egg weight, the number of eggs in the first clutch, total egg weight, hatching success or onset of egg laying. Within pairs active individuals were significantly smaller than their passive partners. Finally, we found a trade-off between clutch size and egg weight. We conclude that our results are in agreement with the gender-ratio hypothesis which states that mating behaviour in hermaphrodites should be flexible and determined by the potential male and female fitness gain in each single mating interaction. Whether the observed interindividual variation in fecundity originates from body-size-dependent sex allocation needs to be studied further. A shift towards the female function as a result of sexual isolation after copulation could explain why active and passive individuals showed similar lifetime fecundities and why effects of body size on fecundity were not observed in active individuals.

Spatial distribution of intertidal fishes: a pattern dependent on body size and predation risk?

Traditionally, heterogeneity levels have been associated with refuge availability and, consequently, with security areas for prey. Hence, there is assumed to be a positive correlation between the spatial distribution of potential victims and habitat heterogeneity levels. Among fish, the magnitude of predator-prey interaction has been associated with their size ratio, which includes body size as a central variable for individual predation risk. To date, the importance of body size and its interaction with spatial heterogeneity in relation to fish spatial distribution has been scarcely considered, being this the main objective of the present study. Based on a semi-experimental design, defined by the level of spatial heterogeneity, censuses in 24 artificial pools were conducted for 2 years at the rocky intertidal zone. This study focused on carnivorous fish assemblages residing off the rocky shore of central Chile. The results indicated a counterintuitive response of fish to spatial heterogeneity, with a higher abundance of small fish in open areas. Apparently, this differential distribution could be related to the size ratio between prey and predator (size-dependent susceptibility to predation), which is a hypothesis supported by decreases in the co-occurrence of fish with increasing size similarity.

Effect of Body Size on Intraguild Predation between Tadpoles of Bamboo-Breeding Poison Frogs and Predaceous Mosquito Larvae

ABSTRACT Our study focused on intraguild predation (IGP) between poison frog tadpoles and predaceous mosquito larvae that use water-filled bamboo internodes as primary microhabitat. We conducted an experiment using artificial pools in southeastern Peru to test the importance of body size of interacting individuals for individual survival. We found that body size strongly affected the outcome of the trophic interaction. We documented a case of symmetric IGP in which members of two phytotelm-breeding species acted as predator or prey depending on their individual and relative body sizes. We found that tadpole relocation by the parent frog may change the relative size of interacting individuals and that priority effects alone cannot be used to predict all outcomes of this interaction.

On the importance of body size in the colonisation of ephemeral resource patches by vagile consumers

A study on the colonisation of leaf detritus patches by vagile macroinvertebrates in a brackish lagoon is presented in the framework of a conceptual model where a body size-related constraint on patch use behaviour is explicitly considered. Abundance patterns of dominant macroinvertebrate taxa were characterised by short-term, non-random fluctuations, showing significant site-dependent variations. Yet, a site-independent covariation was observed between patterns’ fractal dimension and the average body mass of each taxon, indicating that, while the temporal scales characterising the colonisation patterns may be highly species-specific, cross-species generalisations are possible based on body size. The generality of these results was supported by literature data on temporal patterns of carcass colonisation by bathyal fish. The importance of size-related mechanisms in regulating the aggregation of vagile consumers on resource patches and, ultimately, their coexistence at both an inter- and intra-specific level, is discussed.

Small and sensitive to drought: consequences of aridifiation to the conservation of Homopus signatus signatus

Several climate models predict that the western Succulent Karoo in South Africa will aridi-fy. This region includes the range of the smallest tortoise, Homopus signatus signatus. Although the effects of rainfall on the physiology and ecology of H. s. signatus received attention in recent years, the results of these studies have not been integrated to facilitate conservation planning. Here we evaluate the importance of body size and the responses of H. s. signatus to rainfall variation to make recommendations for the taxon's conservation. The small body of H. s. signatus offers one solution to its habitat of low primary productivity and rocky slopes. Nevertheless, female fecundity and egg size increase with female size, and large eggs result in large hatchlings capable of surviving their harsh environment. Females accumulate nutrients in the rainfall season, winter, but also in the dry season, to enable the production of large eggs. Egg production decreases during drought, although some females continue to channel resources to reproduction, apparently at the cost of their own growth. Reduced fecundity and growth, a result of aridification, would likely lower the production of large eggs and hatchlings. Therefore, conservation measures that reduce the mortality of large females may aid population sus-tainability. Because egg and hatchling size might drop below a minimum viable size in an aridified environment, H. s. signatus conservation would benefit from the development of suitable habitat corridors to enable tortoise movements to regions that will receive sufficient rainfall in the future.