Predicting patterns of prey use from morphology of fishes

Synopsis Ecomorphological analyses that search for patterns of association between morphological and prey-use data sets will have a greater chance of understanding the causal relationships between form and diet if the morphological variables used have known consequences for feeding performance. We explore the utility of fish body size, mouth gape and jaw-lever mechanics in predicting patterns of prey use in two very different communities of fishes, Caribbean coral reef fishes, and species of the Centrarchidae that live in Lake Opinicon, Ontario. In spite of major differences in the spectrum of potential prey available, the centrarchids of Lake Opinicon show dietary transitions during ontogeny that are very similar to those seen among and within species of Caribbean groupers (Serranidae). The transition from small zooplankton to intermediate sized invertebrates and ultimately to fishes appears to be very general in ram-suction feeding fishes and is probably driven largely by the constraints of mouth size on prey capture ability. The jaw-lever systems for mouth opening and closing represent direct trade-offs for speed and force of jaw movement. The ratio of in-lever to out-lever in the opening system changes during ontogeny in bluegill, indicating that the mechanics and kinematics of jaw movement may change as well. Among 34 species of Caribbean reef fishes, biting species had jaw-closing ratios that favored force translation, while species that employ rapid-strike ram-suction had closing ratios that enhanced speed of closing and mouth opening ratios that favored a more rapid expansion of the mouth during the strike. We suggest that when prey are categorized into functional groups, reflecting the specific performance features that are important in capturing and handling them, and the differences among habitats in the available prey resource are taken into account, general patterns can be found in morphology-diet relations that cross phylogenetic boundaries.     

The food and feeding relationships of larval and 0+ year juvenile fishes in lowland rivers and connected waterbodies. II. Prey selection and the influence of gape

The relative importance of taxa- and size-specific prey selection, and the influence of gape on the prey consumed by the larvae and 0+ year juveniles of four fish species were investigated in 'main river', 'marina' and 'pond' macrohabitats in the lower River Trent, England. A general sequence of ontogenetic shifts in food consumption was reflected in the electivity indices of particular prey taxa, partly due to the restrictions imposed by the gape of 0+ year fishes. Certain taxa, however, were consistently selected over others, irrespective of size, suggesting that taxa-specific, as well as size-specific, prey characteristics may be important in the selection process. There were significant, positive relationships between maximum prey (zooplankton) length and maximum gape height for larvae, but not for 0+ year juveniles. The majority of fishes, however, consumed prey substantially smaller than the maximum theoretically possible inferred from their gape. The greater size ranges of zooplankton in connected waterbodies compared with main river channels provide suitable prey for a range of developmental steps and fish species, and may, thus, enhance recruitment success.     

Gape size,its morphological basis,and the validity of gape indices in western diamond‐backed rattlesnakes (crotalus atrox)

Maximum gape is important to the ecology and evolution of many vertebrates, particularly gape‐limited predators, because it can restrict the sizes and shapes of prey that can be eaten. Although many cranial elements probably contribute to gape, it is typically estimated from jaw length or jaw width, or occasionally from a combination of these two measures. We measured maximum gape directly for 18 individuals of the western diamond‐backed rattlesnake, Crotalus atrox. We measured each individual's body length, several external cranial dimensions, several cranial osteological dimensions from cleaned skeletons, and we calculated gape index values from two published gape indices (GI). Cranial bone lengths and gape circumference showed negative allometry with snout–vent length (SVL), indicating that small individuals have relatively larger heads and gapes than their larger conspecifics. We then used Akaike's Information Criterion to determine which external and osteological measurements were the best predictors of gape. Body size (SVL) was the best predictor of maximum gape overall; however, when SVL was excluded from the analysis, quadrate (QL) and mandible lengths (MdLs) were the best predictors of maximum gape using both external and osteological measurements. Quadrate length probably contributes directly to gape; however, the importance of MdL to gape is less clear and may be due largely to its allometric relationships with head length and SVL. The two published GI did not prove to be better indicators of actual gape than the jaw and QLs in this study, and the gape values they produced differed significantly from our empirically determined gapes. For these reasons, we urge caution with the use and interpretation of computed GI in future studies. The extensive variation in quadrate and mandible morphology among lineages suggest that these bones are more important to variation in gape among species and lineages than within a single species. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

CLUTCH SIZE AND EGG SIZE IN FREE-LIVING AND PARASITIC COPEPODS: A COMPARATIVE ANALYSIS

The evolution of reproductive strategies and the trade-off between number and size of eggs were investigated in a comparative analysis of free-living and parasitic copepods. Data from 1038 copepod species were used to obtain family averages for 105 families; the phylogenetic relationships among these families include 94 branching events or 94 independent contrasts on which the analysis was based. Transition from a free-living existence to parasitism on invertebrates resulted in small increases in body size. Transition from parasitism on invertebrates to parasitism on fish was associated with greater increases in body size. After controlling for body size, a switch to fish hosts resulted in an increase in the number of eggs produced and a reduction in egg size. Among all contrasts, there was a negative relationship between changes in relative clutch size and changes in relative egg size, suggesting the existence of a trade-off between egg size and numbers. However, opposite changes in these measures of clutch size and egg size were not quite more frequent than expected by chance, therefore indicating that investments into egg numbers are not necessarily made at the expense of egg size, and vice versa. Latitude affected copepod body size, clutch size, and egg size, whereas the effects of freshwater colonization or size of the fish host were not significant. Comparative analyses at either the genus or species levels within given taxa of copepods parasitic on fish provided limited support for a trade-off between clutch size and egg size, but were hampered by the small number of independent phylogenetic contrasts available. From the family-level comparative analysis, it appears that the evolutionary transition from a free life to parasitism on invertebrates, and the transition from parasitism on invertebrates to parasitism on fish, have led to changes in life-history traits in response to the different selective pressures associated with the different modes of life.     

中国陆生哺乳类的易绝灭特征

本研究首先收集了我国367个陆生哺乳类物种的4类基本特征数据:个体大小、繁殖力、利用和濒危等级。从类群和特征两个角度出发,用随机检验和回归分析的方法,检验(1)受威胁物种在各科中是否是随机分布的?如果不是,哪些科含有比随机分布更多或更少的受威胁物种?不同类群受威胁概率与人类的利用有何关系?(2)物种受威胁程度与个体大小和繁殖力有何关系?人类的利用是否对受威胁程度与个体大小和繁殖力的关系产生了重要影响?结果表明:受威胁物种在各科中的分布不是随机的,猴科、牛科和猫科含比随机分布更多的受威胁物种,而鼠科和科则相反;不同类群受威胁概率与被利用率成正比;物种受威胁程度相对于繁殖力和身体大小也不是随机的;当控制系统发育关系的影响后,物种受威胁程度随个体增大和繁殖力降低而增大;多元回归分析显示,只有个体大小与物种受威胁程度相关,这一点与其它的研究不同;个体大小与被利用率成正比。过度利用对我国哺乳类多样性受威胁模式产生了重要影响     

Size-dependent predator–prey relationships between perch and their fish prey

Size-dependent interactions between piscivorous perch Perca fluviatilis (age ≥1 year) and their fish prey age 0 year perch, pikeperch Sander lucioperca and roach Rutilus rutilus in the biomanipulated Bautzen Reservoir indicated that the highest ratio of prey total length ( L _T) to predator L _T was 59%. Perch L _T and prey fish L _T were positively and linearly related. Perch L _T was strongly related with both gape width and gape height. Within the range 80–110 mm L _T, the gape height of perch exceeded gape width, while beginning at 120 mm L _T the gape width exceeded gape height. The minimum, maximum and mean prey L _T and prey body depths of all three prey species increased with increasing predator size, but the increases in mean sizes of perch and pikeperch as prey were less than that of roach. The low limit of the 'predation window' observed in this study coupled with results of previous studies on perch in the Bautzen Reservoir indicated that perch had a major impact on the population dynamics of both perch and pikeperch.     

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

Abstract.  1. A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities.
2. Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees.
3. Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that β diversity was only occasionally greater or less than expected by chance alone.
4. When β diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species.
5. Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. α diversity).
6. Because β diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously.     

Sperm competition and sex change: a comparative analysis across fishes

Current theory to explain the adaptive significance of sex change over gonochorism predicts that female-first sex change could be adaptive when relative reproductive success increases at a faster rate with body size for males than for females. A faster rate of reproductive gain with body size can occur if larger males are more effective in controlling females and excluding competitors from fertilizations. The most simple consequence of this theoretical scenario, based on sexual allocation theory, is that natural breeding sex ratios are expected to be female biased in female-first sex changers, because average male fecundity will exceed that of females. A second prediction is that the intensity of sperm competition is expected to be lower in female-first sex-changing species because larger males should be able to more completely monopolize females and therefore reduce male-male competition during spawning. Relative testis size has been shown to be an indicator of the level of sperm competition, so we use this metric to examine evolutionary responses to selection from postcopulatory male-male competition. We used data from 116 comparable female-first sex-changing and nonhermaphroditic (gonochoristic) fish species to test these two predictions. In addition to cross-species analyses we also controlled for potential phylogenetic nonindependence by analyzing independent contrasts. As expected, breeding sex ratios were significantly more female biased in female-first sex-changing than nonhermaphroditic taxa. In addition, males in female-first sex changers had significantly smaller relative testis sizes that were one-fifth the size of those of nonhermaphroditic species, revealing a new evolutionary correlate of female-first sex change. These results, which are based on data from a wide range of taxa and across the same body-size range for either mode of reproduction, provide direct empirical support for current evolutionary theories regarding the benefits of female-first sex change.     

DOES DIVING LIMIT BRAIN SIZE IN CETACEANS?

We test the longstanding hypothesis, known as the dive constraint hypothesis, that the oxygenation demands of diving pose a constraint on aquatic mammal brain size.Using a sample of 23 cetacean species we examine the relationship among six different measures of relative brain size, body size, and maximum diving duration. Unlike previous tests we include body size as a covariate and perform independent contrast analyses to control for phylogeny. We show that diving does not limit brain size in cetaceans and therefore provide no support for the dive constraint hypothesis. Instead, body size is the main predictor of maximum diving duration in cetaceans. Furthermore, our findings show that it is important to conduct robust tests of evolutionary hypotheses by employing a variety of measures of the dependent variable, in this case, relative brain size.     

Species composition of dabbling duck assemblages: ecomorphological patterns compared with null models

Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.     

Scaling the amplitudes of the circadian pattern of resting oxygen consumption, body temperature and heart rate in mammals

We questioned whether the amplitudes of the circadian pattern of body temperature (T(b)), oxygen consumption (V (O(2))) and heart rate (HR) changed systematically among species of different body weight (W). Because bodies of large mass have a greater heat capacitance than those of smaller mass, if the relative amplitude (i.e., amplitude/mean value) of metabolic rate was constant, one would expect the T(b) oscillation to decrease with the increase in the species W. We compiled data of T(b), V (O(2)) and HR from a literature survey of over 200 studies that investigated the circadian pattern of these parameters. Monotremata, Marsupials and Chiroptera, were excluded because of their characteristically low metabolic rate and T(b). The peak-trough ratios of V (O(2)) (42 species) and HR (35 species) averaged, respectively, 1.57+/-0.08, and 1.35+/-0.07, and were independent of W. The daily high values of T(b) did not change, while the daily low T(b) values slightly increased, with the species W; hence, the high-low T(b) difference (57 species) decreased with W (3.3 degrees C.W(-0.13)). However, the decrease in T(b) amplitude with W was much less than expected from physical principles, and the high-low T(b) ratio remained significantly above unity even in the largest mammals. Thus, it appears that in mammals, despite the huge differences in physical characteristics, the amplitude of the circadian pattern is a fixed (for V (O(2)) and HR), or almost fixed (for T(b)), fraction of the 24-h mean value. Presumably, the amplitudes of the oscillations are controlled parameters of physiological significance.     

REEXAMINING THE RELATIONSHIP BETWEEN BODY SIZE AND TONAL SIGNALS FREQUENCY IN WHALES: A COMPARATIVE APPROACH USING A NOVEL PHYLOGENY

A negative relationship between cetacean body size and tonal sound minimum and maximum frequencies has been demonstrated in several studies using standard statistical approaches where species are considered independent data points. Such studies, however, fail to account for known dependencies among related species—shared similarity due to common ancestry. Here we test these hypotheses by generating the most complete species level cetacean phylogeny to date, which we then use to reconstruct the evolutionary history of body size and standard tonal sounds parameters (minimum, maximum, and center frequency). Our results show that when phylogenetic relationships are considered the correlation between body size (length or mass) and minimum frequency is corroborated with approximately 27% of the variation in tonal sound frequency being explained by body size compared to 86% to 93% explained when phylogenetic relationships are not considered. Central frequency also correlates with body size in toothed whales, but for other tonal sound frequency parameters, including maximum frequency, this hypothesized correlation disappears. Therefore, constraints imposed by body size seem to have played a role in the evolution of minimum frequency but alternative hypotheses are required to explain variation in maximum frequency.     

The assembly of forest communities according to maximum species height along resource and disturbance gradients

An ongoing debate in ecology concerns the relative importance of competition in driving community patterns, especially along gradients of disturbance and productivity. We used a null model to address this question by testing for non‐random organization of forest species according to maximum height, a trait associated with competitive ability for light. Specifically, we compared the species present in 409 different temperate forest plots with the pool of potentially present species (n=639 species), spanning a 50 000 km² area of southern Ontario, Canada. In contrast to current theory, coexisting forest species were neither more similar (i.e. convergent), nor more different (i.e. limiting similarity) in maximum height than expected by chance. However, coexisting forest species had larger maximum heights on average, and their maximum heights were more symmetrically distributed than expected by chance, suggesting that competition has reduced the representation of smaller plant species within plots (i.e. higher turn‐over of species with smaller maximum heights among forest plots). We explored the possibility that our findings resulted from smaller species having relatively narrower niches; however, a conclusive test of this explanation will require knowledge of fundamental, rather than realized niche breadth. We also tested the prediction that the influence of competition changes along gradients of productivity and disturbance by examining how the effect size of our null model tests changed along these gradients. We observed that species with smaller maximum heights were increasingly under‐represented in more productive forest communities, suggesting an increased role for competition in determining species membership in more productive communities. In contrast to theory, however, the effect size of our tests did not significantly change along a gradient of forest disturbance. In summary, we found evidence that maximum species height plays a significant role in driving the non‐random organization of plant species among hundreds of mature forest plots, and that this role is more pronounced in more productive forest plots. 1     

Assembly rules for New England ant assemblages

Community assembly rules specify patterns of species co-occurrence and morphology dictated by interspecific competition. We collected data on the occurrence of ground-foraging ant species in 22 ombrotrophic bogs and adjacent forest plots of New England to test two general assembly rules: reduced co-occurrence of species among communities, and even spacing of body sizes of species within communities. We used null models to generate random communities unstructured by competition and evaluated patterns at regional and local spatial scales. At the regional scale, species co-occurrence in forests, but not bogs, was less than expected by chance, whereas, at the local scale, co-occurrence in both habitats was not different from random. At the regional scale, spacing of body size distributions was random (in bogs) or aggregated (in forests). At the local scale, body size patterns were weakly segregated in bogs, but random or weakly aggregated in forests. In bogs, size ratio constancy was accompanied by greater generic diversity than expected. Although assembly rules were originally developed for vertebrate communities, they successfully explained some patterns in New England ant assemblages. However, the patterns were contingent on spatial scale, and were distinctly different for bog and forest communities, despite their close proximity and the presence of many shared species in both assemblages. The harsh physical conditions of bogs may act as a habitat filter that alters community assembly rules.     

Sexual dimorphism and ontogenetic allometry of soft tissues in Rattus norvegicus.

Most studies of sexual dimorphism in mammals focus on overall body size. However, relatively little is known about the differences in growth trajectories that produce dimorphism in organ and muscle size. We weighed six organs and four muscles in Rattus norvegicus to determine what heterochronic and allometric scaling differences exist between the sexes. This cross-sectional growth study included 113 males and 109 females with ages ranging from birth to 200 days of age. All muscle and organ weights were ultimately greater in males than in females, because males grew for a longer period of time, had a greater maximum rate of growth, and spent more time near the maximum rate. No ontogenetic scaling differences existed between the sexes in organ weight except for lungs and gonads. During growth, organ weights were negatively allometric to body weight. No scaling differences relative to body weight existed between the sexes for muscles; however, there was variation in the allometric relations among muscles relative to body weight. Sexual dimorphism in muscles and organs appears to be a size difference resulting from differences in the duration and rates of growth.     

Body-size differences in a colonizing amphipod-mollusc assemblage

Summary We examined body size patterns in a colonizing assemblage of marine amphipods and molluscs. We collected animals over a 25 day period from an archipelago of pits that were drilled in brick surfaces. The percent of pits occupied, abundance, species richness, and body size of colonists all increased significantly through time. We compared size ratios of coexisting species with two null models, one that randomized individuals and one that randomized species-populations. For both models, observed overlap ratios usually did not differ from randomness, although species richness was consistently lower than expected for later samples. Results were similar for a subset of the data, a guild of suspension/deposit feeding amphipod species. Some assemblages did show significant deviations from the null models, but the results were spotty and varied among replicates. Overall, the evidence for non-random overlap ratios in body sizes of colonizers was weak.     

Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths

1. Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.
2. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.
3. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.
4. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.
5. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

     

No support for Heincke's law in hagfish (Myxinidae): lack of an association between body size and the depth of species occurrence

This study tests for interspecific evidence of Heincke's law among hagfishes and advances the field of research on body size and depth of occurrence in fishes by including a phylogenetic correction and by examining depth in four ways: maximum depth, minimum depth, mean depth of recorded specimens and the average of maximum and minimum depths of occurrence. Results yield no evidence for Heincke's law in hagfishes, no phylogenetic signal for the depth at which species occur, but moderate to weak phylogenetic signal for body size, suggesting that phylogeny may play a role in determining body size in this group.     

Extinction and the loss of functional diversity

Although it is widely thought to influence ecosystem processes, there is little consensus on an appropriate measure of functional diversity. The two major perspectives, to date, are to assume that every species is functionally unique, or to assume that some species are functionally identical, such that functional groups exist. Using a continuous measure of functional diversity (FD) derived from the quantitative functional traits of species, we show that the loss of functional diversity from six natural assemblages was rapid compared with rates of loss from comparable simulated assemblages. Loss of FD occurred faster than loss of functional-group diversity in four of the six natural assemblages. Patterns of functional-group diversity loss depended on the number of functional groups and the number of species in an assemblage. Extinctions that occurred first for species with particular traits (e.g. low leaf nitrogen concentration, deep roots and large body size) caused greater loss of FD than expected by chance in four of the six natural assemblages. In two real assemblages, these trait-dependent extinctions had more severe effects on FD than our simulated worst-case extinction scenario. These data suggest that conserving a large proportion of the functional traits of species requires conserving a large proportion of all species.     

Queen/worker thorax volume ratios and nest-founding strategies in ants

Queen/worker thorax volume ratios were calculated in nine monogynous, seven polygynous and eight parasitic ant species in order to determine whether mode of nest founding is reflected in relative gyne size. A significant difference in this ratio was found between monogynous (independent nest founders) and polygynous and parasitic species (dependent nest founders). Thorax volume ratio in ants appears to be independent of actual gyne or worker size and can be used as a relative measure sure of colony investment in the gynes. Furthermore, thorax volume ratio seems to reflect the mode of nestfounding behaviour when compared between species within genera as well as among species in general. Polygyny is discussed as a nest-founding strategy that is selected for when nest founding by single gynes is difficult and costly. In addition, secondary benefits could be gained by polygynous colonies since investment in gyne size could be decreased.