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139 results for “predator size”
Data from: Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises
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Data from: Nest predation risk explains variation in avian clutch size
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Data for the article entitled: Linking sexual size dimorphism to trophic niche partitioning in a generalist predator
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Prey size mediates interference competition and predation dynamics in a large carnivore community
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Data from: Seed size predicts global effects of small mammal seed predation on plant recruitment
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Data from: The sources of variation for individual prey-to-predator size ratios
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No impact of biocontrol agent’s predation cues on development time or size of surviving Aedes albopictus under optimal nutritional availability
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Data from: The evolution of eye size in response to increased fish predation in Daphnia
Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator-induced mortality has recently been identified as a potential driver of eye size variation. Here we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild-caught and third generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild-caught specimens did not differ in eye size across all lakes. However, third generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.
Predator population size structure alters consumption of prey from epigeic and grazing food webs
<p>Numerous studies have found that predators can suppress prey densities and thereby impact important ecosystem processes such as plant productivity and decomposition. However, prey suppression by spiders can be highly variable. Unlike predators that feed on prey within a single energy channel, spiders often consume prey from asynchronous energy channels, such as grazing (live plant) and epigeic (soil surface) channels. Spiders undergo few life cycle changes and thus appear to be ideally suited to link energy channels, but ontogenetic diet shifts in spiders have received little attention. For example, spider use of different food channels may be highly specialized in different life stages and thus a species may be a multichannel omnivore only when we consider all life stages. Using stable isotopes, we investigated whether wolf spider (Pardosa littoralis, henceforth Pardosa) prey consumption is driven by changes in spider size. Small spiders obtained > 80% of their prey from the epigeic channel, whereas larger spiders used grazing and epigeic prey almost equally. Changes in prey consumption were not driven by changes in prey density, but by changes in prey use by different spider size classes. Thus, because the population size structure of Pardosa changes dramatically over the growing season, changes in spider size may have important implications for the strength of trophic cascades. Our research demonstrates that life history can be an important component of predator diet, which may in turn affect community- and ecosystem-level processes.</p>
Anti-predator behaviour depends on male weapon size
<p>Tonic immobility and escape are adaptive anti-predator tactics used by many animals. Escape requires movement, whereas tonic immobility does not. If anti-predator tactics relate to weapon size, males with larger weapons may adopt tonic immobility, whereas males with smaller weapons may adopt escape. However, no study has investigated the relationship between weapon size and anti-predator tactics. In this study, we investigated the relationship between male weapon size and tonic immobility in the beetle <i>Gnathocerus</i><i> cornutus</i>. The results showed that tonic immobility was more frequent in males with larger weapons. Although most studies of tonic immobility in beetles have focused on the duration, rather than the frequency, tonic immobility duration was not affected by weapon size in <i>G</i>.<i> cornutus</i>. Therefore, this study is the first to suggest that the male weapon trait affects anti-predator tactics.</p>
Size, not temperature, drives cyclopoid copepod predation of invasive mosquito larvae
<p class="CxSpFirst">During range expansion, invasive species can experience new thermal regimes. Differences between the thermal performance of local and invasive species can alter species interactions, including predator-prey interactions. The Asian tiger mosquito, <i>Aedes albopictus</i>, is a known vector of several viral diseases of public health importance. It has successfully invaded many regions across the globe and currently threatens to invade regions of the UK where conditions would support seasonal activity. We assessed the functional response and predation efficiency (percentage of prey consumed) of the cyclopoid copepods <em>Macrocyclops albidus</em> and <em>Megacyclops viridis</em> from South East England, UK against newly-hatched French <em>Ae. albopictus</em> larvae across a relevant temperature range (15, 20, and 25ºC). Predator-absent controls were included in all experiments to account for background prey mortality. We found that both <i>M. albidus</i> and<i> M. viridis </i>display type II functional response curves, and that both would therefore be suitable biocontrol agents in the event of an <i>Ae. albopictus</i> invasion in the UK. No significant effect of temperature on the predation interaction was detected by either type of analysis. However, the predation efficiency analysis did show differences due to predator species. The results suggest that <i>M. viridis</i> would be a superior predator against invasive <i>Ae. albopictus</i> larvae due to the larger size of this copepod species, relative to <i>M. albidus</i>. Our work highlights the importance of size relationships in predicting interactions between invading prey and local predators.</p>
Data from: Early plant development depends on embryo damage location: the role of seed size in partial seed predation
<p>Data on 1) Observed weevil-infested acorns in the field; 2) Germination rates and times, and seedling emergence of control and embryo-damaged acorns; 3) Seedling performance and physiology of seedlings</p>
Data from: Allometric scaling of indirect effects: body size ratios predict non-consumptive effects in multi-predator systems
1. Non-consumptive effects (NCES) frequently lead to non-independent effects of multiple predators. While such emergent predator effects are ubiquitous in natural communities, the strength of these effects varies among studies and systems, making it difficult to predict a priory how changes in predator diversity influence prey suppression. Thus, identifying general scaling rules which can explain this variation of non-independent effects is vital for modeling natural communities and how they respond to biodiversity loss. 2. Body size is a key trait determining the nature and strength of ecological interactions. While great progress has been made using allometric relationships to predict the interaction strength of predator-prey pairs, it is unknown whether similar relationships explain variation in the strength of NCEs, and how they are related to consumptive effects. 3. Here we experimentally manipulate the relative size difference of multiple predators to determine whether NCEs follow general allometric scaling relationships in an aquatic multi-predator system. 4. Results demonstrate that the presence and strength of NCEs can vary dramatically across predator combinations. However, this variation scaled predictably with the size ratio of predators; increasing the size difference among predators increased NCEs. This pattern was driven by a size-mediated shift in "food web motif" from competition to intraguild predation and a positive correlation of NCEs and intraguild predation rate. 5. Results indicate that models which assume that consumers have independent effects are particularly likely to make erroneous predictions when predators differ substantially in size, but simple allometric relationships of NCEs could be used to correct this bias.
Data from: Size selection by a gape-limited predator of a marine snail: insights into magic traits for speciation
The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to be wave adapted and predatory shore crab adapted, but the magnitude and targets of predator-driven selection are unknown. In Spain, a small, wave ecotype with a large aperture from the lower shore and a large, thick-shelled crab ecotype from the upper shore meet in the mid-shore and show partial size-assortative mating. We performed complementary field tethering and laboratory predation experiments; the first set compared the survival of two different size-classes of the crab ecotype while the second compared the same size-class of the two ecotypes. In the first set, the large size-class of the crab ecotype survived significantly better than the small size-class both on the upper shore and in the laboratory. In the second set, the small size-class of the crab ecotype survived substantially better than that of the wave ecotype both on the upper shore and in the laboratory. Shell-breaking predation on tethered snails was almost absent within the lower shore. In the laboratory shore crabs (Pachygrapsus marmoratus) with larger claw heights selected most strongly against the small size-class of the crab ecotype, whereas those with medium claw heights selected most strongly against the thin-shelled wave ecotype. Sexual maturity occurred at a much larger size in the crab ecotype than in the wave ecotype. Our results showed that selection on the upper shore for rapid attainment of a size refuge from this gape-limited predator favors large size, thick shells, and late maturity. Model parameterization showed that size-selective predation restricted to the upper shore resulted in the evolution of the crab ecotype despite gene flow from the wave ecotype snails living on the lower shore. These results on gape-limited predation and previous ones showing size-assortative mating between ecotypes suggest that size may represent a magic trait for the thick-shelled ecotype.
Data from: Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators
The extinct shark Carcharocles megalodon is one of the largest marine apex predators ever to exist. Nonetheless, little is known about its body-size variations through time and space. Here, we studied the body-size trends of C. megalodon through its temporal and geographic range to better understand its ecology and evolution. Given that this species was the last of the megatooth lineage, a group of species that shows a purported size increase through time, we hypothesized that C. megalodon also displayed this trend, increasing in size over time and reaching its largest size prior to extinction. We found that C. megalodon body-size distribution was left-skewed (suggesting a long-term selective pressure favoring larger individuals), and presented significant geographic variation (possibly as a result of the heterogeneous ecological constraints of this cosmopolitan species) over geologic time. Finally, we found that stasis was the general mode of size evolution of C. megalodon (i.e., no net changes over time), contrasting with the trends of the megatooth lineage and our hypothesis. Given that C. megalodon is a relatively long-lived species with a widely distributed fossil record, we further used this study system to provide a deep-time perspective to the understanding of the body-size trends of marine apex predators. For instance, our results suggest that (1) a selective pressure in predatory sharks for consuming a broader range of prey may favor larger individuals and produce left-skewed distributions on a geologic time scale; (2) body-size variations in cosmopolitan apex marine predators may depend on their interactions with geographically discrete communities; and (3) the inherent characteristics of shark species can produce stable sizes over geologic time, regardless of the size trends of their lineages.
Data from: Testes mass in the livebearing fish Brachyrhaphis rhabdophora (Poeciliidae) varies hypoallometrically with body size but not between predation environments
In this study, we considered potential causes of variation in testis size in the livebearing fish Brachyrhaphis rhabdophora. We evaluated variation in testes mass among individual males and among populations that occupy different selective environments. First, we predicted that small males should allocate more to testes mass than large males (i.e., hypoallometric pattern) based on a sperm competition argument. Second, based on life history theory and associated differences in mortality rates between populations that co-exist with many fish predators and those with few predators, we predicted that males in high-predation environments should allocate more to testes mass than males in habitats with few predators. Small males allocated proportionally more to testes mass than larger males (slope of testes mass to body mass was hypoallometric). However, there was no effect of predator environment on testes mass independent of body size differences. In this system, size-specific patterns of reproductive allocation in males (hypoallometry) differ from that seen in females (hyperallometry). Allocation to testes mass may respond to differences in mortality rate through selection on body size.
Data from: Patchy distribution and low effective population size raise concern for an at-risk top predator
Aim: Understanding carnivore distribution is important for management decisions that aim to restore naturally-regulated ecosystems and preserve biodiversity. Eastern Wolves, a species at risk in Canada, are centralized in Algonquin Provincial Park and their ability to disperse and establish themselves elsewhere is limited by human-caused mortality associated with hunting, trapping, and vehicle collisions. Here, we refine our understanding of Eastern Wolf distribution and provide the first estimates of their effective population size. Location: Southern Ontario and Gatineau Quebec. Methods: We used noninvasive samples, as well as blood samples archived from other research projects, collected between 2010 – 2014 to generate autosomal microsatellite genotypes at 12 loci for 98 Canis individuals. We utilized Bayesian and multivariate clustering analyses to identify Eastern Wolves in regions that were previously unsampled. Both linkage disequilibrium and temporal approaches were used to estimate effective population size of Eastern Wolves. Results: Assignment tests identified 34 individuals as Eastern Wolves, primarily in or near two provincial parks: Killarney and Queen Elizabeth II Wildlands. Eastern Coyotes were identified in Bon Echo Provincial Park, Frontenac Provincial Park, and Gatineau Park, whereas many of the samples were admixed among the different Canis types. Effective population size (Ne) estimates ranged from 24.3 – 122.1 with a harmonic mean of 45.6. Main Conclusions: The identification of Eastern Wolves in the regions of Killarney and Queen Elizabeth II Wildlands Provincial Parks extends the range of Eastern Wolves north of the French River and southward into previously unidentified regions. The effective population size is low and raises concerns for long-term persistence of this threatened carnivore; values are dangerously close to critical values recommended for short-term persistence. These results provide important information for upcoming Eastern Wolf recovery plans associated with federal and provincial endangered species legislation.
Data from: Predator size divergence depends on community context
Body size is a multi-functional trait related to various fitness components, but the relative importance of different selection pressures are seldom resolved. In Carabus japonicus beetles, of which the larvae exclusively prey on earthworms, adult body size is related to the presence/absence of a larger congener and habitat temperature. In sympatry, C. japonicus consistently exhibits smaller body size which is effective for avoiding interspecific mating, but in allopatry, it shows size variation unrelated to temperature. Here, we show that this predator-size variation is attributed to prey-size variation, associated with high phylogenetic diversity in earthworm communities. In allopatry, the predator size was larger where larger prey occurred. Larger adult size may have been selected because larger females produce larger larvae, which can subdue larger prey. Thus, in the absence of a larger congener, variation in prey body size had a pronounced effect on geographic body size divergence in C. japonicus.
Data from: Evolutionary divergence of adult body size and juvenile growth in sympatric subpopulations of a top predator in aquatic ecosystems
Evolutionary theory predicts that different selective regimes may contribute to divergent evolution of body size and growth rate among populations, but most studies have focused on allopatric populations. Here, we studied five sympatric subpopulations of anadromous northern pike (Esox lucius) in the Baltic Sea subjected to allopatric habitats for a short period of their life cycle due to homing behavior. We report differences in adult body size among subpopulations that were in part due to variation in growth rate. Body size of emigrating juveniles also differed among subpopulations, and differences remained when individuals were reared in a common environment, thus indicating evolutionary divergence among subpopulations. Furthermore, a QST-FST comparison indicated that differences had evolved due to divergent selection rather than genetic drift, possibly in response to differences in selective mortality among spawning habitats during the allopatric life stage. Adult and juvenile size were negatively correlated across subpopulations, and reconstruction of growth trajectories of adult fishes suggested that body size differences developed gradually and became accentuated throughout the first years of life. These results represent rare evidence that sympatric subpopulations can evolve differences in key life-history traits despite being subjected to allopatric habitats during only a very short fraction of their life.
Data from: Intraspecific predator inhibition, not a prey size refuge, enables oyster population persistence during predator outbreaks
Predators commonly structure natural communities, but predation effects can vary greatly. For example, increasing predator densities may not reduce prey populations as expected if intraspecific predator interactions suppress foraging efficiency or if prey size refuges exist. In northeastern Florida (USA), outbreaks of the predatory crown conch Melongena corona have contributed to declines in oyster populations and the commercial oyster fishery. However, despite expectations of oyster population collapse, reefs have persisted, albeit with reduced adult oyster size and living reef biomass. To investigate the mechanism(s) underlying this unexpected persistence, we used field observations and experiments to examine the effects of predator density and prey size on predation rates. Multi-year surveys indicated that large oysters did not experience a predation size refuge, and further suggested that predation rates declined with increased predator density. Consistent with field surveys, field experiments demonstrated that conchs selectively consumed larger oysters (potentially explaining the absence of large oysters on natural reefs) and that high conch densities suppressed per capita predation rates, likely due to intraspecific antagonistic interactions. A Type III ratio-dependent model best described the experimental conch functional response, explaining >50% of the variation in per capita prey consumption and including a signal of reduced attack rates at high predator densities. Thus, although large aggregations of predators have the potential to deplete prey populations, our study illustrates intraspecific predator interactions that possibly prevent the local extirpation of an important habitat-forming prey species.
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