Nutrient cycling in most terrestrial ecosystems is controlled by moisture-dependent decomposer ac... more Nutrient cycling in most terrestrial ecosystems is controlled by moisture-dependent decomposer activity. In arid ecosystems, plant litter cycling exceeds rates predicted based on precipitation amounts, suggesting that additional factors are involved. Attempts to reveal these factors have focused on abiotic degradation, soil–litter mixing and alternative moisture sources. Our aim was to explore an additional hypothesis that macro-detritivores control litter cycling in deserts. We quantified the role different organisms play in clearing plant detritus from the desert surface, using litter baskets with different mesh sizes that allow selective entry of micro-, meso- or macrofauna. We also measured soil nutrient concentrations in increasing distances from the burrows of a highly abundant macro-detritivore, the desert isopod <i>Hemilepistus reaumuri</i>. Macro-detritivores controlled the clearing of plant litter in our field site. The highest rates of litter removal were measured during the hot and dry summer when isopod activity peaks and microbial activity is minimal. We also found substantial enrichment of inorganic nitrogen and phosphorous near isopod burrows. We conclude that burrowing macro-detritivores are important regulators of litter cycling in this arid ecosystem, providing a plausible general mechanism that explains the unexpectedly high rates of plant litter cycling in deserts.
Many animals undergo dramatic changes in colour during development1,2. Changes in predation risk ... more Many animals undergo dramatic changes in colour during development1,2. Changes in predation risk during ontogeny are associated with spectacular switches in defensive colours, typically involving the replacement of skin or the production of new pigment cells3. Ontogenetic colour systems are ideal models for understanding the evolution and formation mechanisms of animal colour which remain largely enigmatic2. We show that defensive colour switching in lizards arises by reorganization of a single photonic system, as an incidental by-product of chromatophore maturation. The defensive blue tail colour of hatchling A. beershebensis lizards is produced by light scattering from premature guanine crystals in underdeveloped iridophore cells. Camouflaged adult tail colours emerge upon reorganization of the guanine crystals into a photonic reflector during chromatophore maturation. The substituent guanine crystals form by the attachment of individual nanoscopic plates, which coalesce during gr...
Ontogenetic changes in color and pattern that are not directly related to reproduction are very c... more Ontogenetic changes in color and pattern that are not directly related to reproduction are very common yet remain a poorly understood phenomenon. One example is conspicuous colors in the tails of fish, amphibians, and reptiles that fade out later in life. We suggest a novel hypothesis: conspicuous tail colors that appear only in juveniles compensate for an increased activity level, deflecting imminent attacks to the tail. We observed blue-tailed, newly hatched lizards (Acanthodactylus beershebensis) in the field and compared 5 behavioral parameters with those of older individuals that had already lost their neonate coloration. In addition, we explored whether tail displays, often assumed to direct a predator’s attention to the tail, disappear with the color change. Striped blue-tailed hatchlings foraged more actively than 3-week-old juveniles, spent a longer time in open microhabitats, and performed deflective tail displays. In comparison, 2 other lacertids that do not undergo ontog...
Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorgan... more Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorganism activity, among other things. Decomposition models typically underestimate rates of plant litter decomposition in drylands, suggesting the existence of additional drivers of decomposition. Attempts to reveal these drivers have predominantly focused on abiotic degradation agents, alternative moisture sources, and soil–litter mixing. The role of burrowing animals in promoting decomposition has received less attention despite greatly contributing to plant litter transfer from the harsh desert surface to the moister and nutrient-rich environment belowground. Our goal was to explore how macro-detritivore burrows affect plant litter mineralization dynamics. We introduced 13 C-labeled litter belowground into (1) desert isopod ( Hemilepistus reaumuri ) burrows and (2) artificial burrows, and aboveground on top of (3) isopod fecal pellet mounds and (4) bare soil crust. We compared the litter ...
Abstract Movement‐based indices such as moves per minute (MPM) and proportion time moving (PTM) a... more Abstract Movement‐based indices such as moves per minute (MPM) and proportion time moving (PTM) are common methodologies to quantify foraging behaviour. We explore fundamental drawbacks of these indices that question the ways scientists have been using them and propose new solutions. To do so, we combined analytical and simulation models with lizards foraging data at the individual and species levels. We found that the maximal value of MPM is constrained by the minimal durations of moves and stops. As a result, foragers that rarely move and those that rarely stop are bounded to similar low MPM values. This implies that (1) MPM has very little meaning when used alone, (2) MPM and PTM are interdependent, and (3) certain areas in the MPM‐PTM plane cannot be occupied. We also found that MPM suffers from inaccuracy and imprecision. We introduced a new bias correction formula for already published MPM data, and a novel index of changes per minute (CPM) that uses the frequency of changes between move and stop bouts. CPM is very similar to MPM, but does not suffer from bias. Finally, we suggested a new foraging plane of average move and average stop durations. We hope that our guidelines of how to use (and not to use) movement‐based indices will add rigor to the study of animals’ foraging behaviour.
Predators often feed on a wide range of prey that can vary in behavior, morphology, and physiolog... more Predators often feed on a wide range of prey that can vary in behavior, morphology, and physiology. The net benefits that predators gain from prey are likely related to both prey nutrient content and prey morphology or defenses. For invertebrates, the exoskeleton is a morphological trait that varies widely among species and during ontogeny and could affect nutrient extraction by predators. The goal of this study was to determine how prey exoskeleton content affected predator nutrient intake, assimilation, and excretion by comparing spiders feeding on either larval or adult mealworms of similar size. We found that the proportion of prey energy invested in digestion was greatest in spiders consuming adult mealworm beetles which had higher amounts of exoskeleton than larvae. Further, spiders extracted a greater proportion of elements, macronutrients, and energy from the larval mealworms, which had lower amounts of exoskeleton. Interestingly, total nitrogen content of prey was not a predictor of nitrogen assimilation as spiders assimilated more nitrogen from the larval mealworms, which had lower total nitrogen content. While adult beetles had higher total nitrogen content, their discarded remains of prey had large amounts of nitrogen that was nutritionally unavailable for spiders (i.e., exoskeleton). These results suggest that prey exoskeleton can affect assimilation efficiency by predators, and that a combination of macronutrient and elemental analyses may be needed to examine the quality of prey for predators and the potential consequences of predation for nutrient flows (e.g., consumer assimilation, egestion, and excretion) in ecosystems.
Abstract Predator induced trait mediated indirect interactions (TMIIs) are likely the dominant fa... more Abstract Predator induced trait mediated indirect interactions (TMIIs) are likely the dominant facet of trophic interactions in aboveground food-webs. New research is beginning to show that TMIIs are also important in revealing how soil food-webs (SFWs) regulate biogeochemical processes. We suggest that TMIIs can modify SFW functions by (a) regulating the quantity and nutritional quality of plants and animal production known to drive the SFW, (b) inducing defense phenotypes in soil-organisms, and (c) changing soil environmental conditions. Currently, very few studies have explored the role TMIIs play in shaping SFW functions, especially the cascading effects on SFW dynamics. Much theoretical and empirical research is needed before we can successfully incorporate the non-consumptive effects of predation into SFW models.
Summary Understanding the ecological function of an animal's pigmentation pattern is an intri... more Summary Understanding the ecological function of an animal's pigmentation pattern is an intriguing research challenge. We used quantitative information on lizard foraging behaviour to search for movement correlates of patterns across taxa. We hypothesized that noticeable longitudinal stripes that enhance escape by motion dazzle are advantageous for mobile foragers that are highly detectable against the stationary background. Cryptic pigmentation patterns are beneficial for less-mobile foragers that rely on camouflage to reduce predation. Using an extensive literature survey and phylogenetically controlled analyses, we found that striped lizards were substantially more mobile than lizards with cryptic patterns. The percentage of time spent moving was the major behavioural index responsible for this difference. We provide empirical support for the hypothesized association between lizard dorsal pigmentation patterns and foraging behaviour. Our simple yet comprehensive explanation may be relevant to many other taxa that present variation in body pigmentation patterns.
Background/Question/Methods The process of energy and materials transfer governs ecosystem produc... more Background/Question/Methods The process of energy and materials transfer governs ecosystem production, food chain length and species diversity. Herbivores are pivotal in this process because their low plant assimilation efficiencies constrain transfer rates and ecosystem carbon: nitrogen balance. Theory suggests that physiological stress due to predation risk could be an important determinant of trophic transfer efficiency and ecosystem nutrient budget. We tested this assertion in a series of field and laboratory experiments. We reared grasshopper herbivore nymphs with or without risk of spider predation and measured their metabolic rate, nutritional requirements, and excretion and body elemental composition. We also calculated how the risk of spider predation affects elemental composition of uneaten plant material entering the soil organic matter pool. Results/Conclusions We show that shifting nutrient demand of herbivores facing predation risk causes carbohydrate carbon to become ...
Background/Question/Methods The physiological reaction of prey to predation involves allocating r... more Background/Question/Methods The physiological reaction of prey to predation involves allocating resources from production to support emergency functions. An example of such a reaction is an increase in maintenance respiration concomitant with higher carbohydrate and lower N demand. Such changes in prey energy and elemental budget should alter the role prey play in regulating the quality of detrital inputs to soils. Nutrient content of detritus is an important determinant of the way soil communities regulate ecosystem processes. Thus, the physiological reaction of prey to predation can potentially explicate changes in ecosystem functioning. Results/Conclusions First empirical examination using an old-field model food-chain of an herbivore grasshopper (prey) and a predatory spider, thus far, support this new conceptual framework. Grasshoppers stressed by spider predators prefer to eat more carbohydrates and have a higher body carbon-to-nitrogen ratio than do grasshoppers raised withou...
The concentration of 11 trace elements (Mg, Al, Mn, Cu, Zn, Rb, Mo, Cd, Ba, Hg and Pb) and sulfur... more The concentration of 11 trace elements (Mg, Al, Mn, Cu, Zn, Rb, Mo, Cd, Ba, Hg and Pb) and sulfur in feathers of pigeons and ravens was determined by ICPMS after wet digestion of the sample. Pigeon feathers were collected from five habitats: rural, industrial, urban, natural ...
Nutrient cycling in most terrestrial ecosystems is controlled by moisture-dependent decomposer ac... more Nutrient cycling in most terrestrial ecosystems is controlled by moisture-dependent decomposer activity. In arid ecosystems, plant litter cycling exceeds rates predicted based on precipitation amounts, suggesting that additional factors are involved. Attempts to reveal these factors have focused on abiotic degradation, soil–litter mixing and alternative moisture sources. Our aim was to explore an additional hypothesis that macro-detritivores control litter cycling in deserts. We quantified the role different organisms play in clearing plant detritus from the desert surface, using litter baskets with different mesh sizes that allow selective entry of micro-, meso- or macrofauna. We also measured soil nutrient concentrations in increasing distances from the burrows of a highly abundant macro-detritivore, the desert isopod <i>Hemilepistus reaumuri</i>. Macro-detritivores controlled the clearing of plant litter in our field site. The highest rates of litter removal were measured during the hot and dry summer when isopod activity peaks and microbial activity is minimal. We also found substantial enrichment of inorganic nitrogen and phosphorous near isopod burrows. We conclude that burrowing macro-detritivores are important regulators of litter cycling in this arid ecosystem, providing a plausible general mechanism that explains the unexpectedly high rates of plant litter cycling in deserts.
Many animals undergo dramatic changes in colour during development1,2. Changes in predation risk ... more Many animals undergo dramatic changes in colour during development1,2. Changes in predation risk during ontogeny are associated with spectacular switches in defensive colours, typically involving the replacement of skin or the production of new pigment cells3. Ontogenetic colour systems are ideal models for understanding the evolution and formation mechanisms of animal colour which remain largely enigmatic2. We show that defensive colour switching in lizards arises by reorganization of a single photonic system, as an incidental by-product of chromatophore maturation. The defensive blue tail colour of hatchling A. beershebensis lizards is produced by light scattering from premature guanine crystals in underdeveloped iridophore cells. Camouflaged adult tail colours emerge upon reorganization of the guanine crystals into a photonic reflector during chromatophore maturation. The substituent guanine crystals form by the attachment of individual nanoscopic plates, which coalesce during gr...
Ontogenetic changes in color and pattern that are not directly related to reproduction are very c... more Ontogenetic changes in color and pattern that are not directly related to reproduction are very common yet remain a poorly understood phenomenon. One example is conspicuous colors in the tails of fish, amphibians, and reptiles that fade out later in life. We suggest a novel hypothesis: conspicuous tail colors that appear only in juveniles compensate for an increased activity level, deflecting imminent attacks to the tail. We observed blue-tailed, newly hatched lizards (Acanthodactylus beershebensis) in the field and compared 5 behavioral parameters with those of older individuals that had already lost their neonate coloration. In addition, we explored whether tail displays, often assumed to direct a predator’s attention to the tail, disappear with the color change. Striped blue-tailed hatchlings foraged more actively than 3-week-old juveniles, spent a longer time in open microhabitats, and performed deflective tail displays. In comparison, 2 other lacertids that do not undergo ontog...
Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorgan... more Litter decomposition in most terrestrial ecosystems is regulated by moisture-dependent microorganism activity, among other things. Decomposition models typically underestimate rates of plant litter decomposition in drylands, suggesting the existence of additional drivers of decomposition. Attempts to reveal these drivers have predominantly focused on abiotic degradation agents, alternative moisture sources, and soil–litter mixing. The role of burrowing animals in promoting decomposition has received less attention despite greatly contributing to plant litter transfer from the harsh desert surface to the moister and nutrient-rich environment belowground. Our goal was to explore how macro-detritivore burrows affect plant litter mineralization dynamics. We introduced 13 C-labeled litter belowground into (1) desert isopod ( Hemilepistus reaumuri ) burrows and (2) artificial burrows, and aboveground on top of (3) isopod fecal pellet mounds and (4) bare soil crust. We compared the litter ...
Abstract Movement‐based indices such as moves per minute (MPM) and proportion time moving (PTM) a... more Abstract Movement‐based indices such as moves per minute (MPM) and proportion time moving (PTM) are common methodologies to quantify foraging behaviour. We explore fundamental drawbacks of these indices that question the ways scientists have been using them and propose new solutions. To do so, we combined analytical and simulation models with lizards foraging data at the individual and species levels. We found that the maximal value of MPM is constrained by the minimal durations of moves and stops. As a result, foragers that rarely move and those that rarely stop are bounded to similar low MPM values. This implies that (1) MPM has very little meaning when used alone, (2) MPM and PTM are interdependent, and (3) certain areas in the MPM‐PTM plane cannot be occupied. We also found that MPM suffers from inaccuracy and imprecision. We introduced a new bias correction formula for already published MPM data, and a novel index of changes per minute (CPM) that uses the frequency of changes between move and stop bouts. CPM is very similar to MPM, but does not suffer from bias. Finally, we suggested a new foraging plane of average move and average stop durations. We hope that our guidelines of how to use (and not to use) movement‐based indices will add rigor to the study of animals’ foraging behaviour.
Predators often feed on a wide range of prey that can vary in behavior, morphology, and physiolog... more Predators often feed on a wide range of prey that can vary in behavior, morphology, and physiology. The net benefits that predators gain from prey are likely related to both prey nutrient content and prey morphology or defenses. For invertebrates, the exoskeleton is a morphological trait that varies widely among species and during ontogeny and could affect nutrient extraction by predators. The goal of this study was to determine how prey exoskeleton content affected predator nutrient intake, assimilation, and excretion by comparing spiders feeding on either larval or adult mealworms of similar size. We found that the proportion of prey energy invested in digestion was greatest in spiders consuming adult mealworm beetles which had higher amounts of exoskeleton than larvae. Further, spiders extracted a greater proportion of elements, macronutrients, and energy from the larval mealworms, which had lower amounts of exoskeleton. Interestingly, total nitrogen content of prey was not a predictor of nitrogen assimilation as spiders assimilated more nitrogen from the larval mealworms, which had lower total nitrogen content. While adult beetles had higher total nitrogen content, their discarded remains of prey had large amounts of nitrogen that was nutritionally unavailable for spiders (i.e., exoskeleton). These results suggest that prey exoskeleton can affect assimilation efficiency by predators, and that a combination of macronutrient and elemental analyses may be needed to examine the quality of prey for predators and the potential consequences of predation for nutrient flows (e.g., consumer assimilation, egestion, and excretion) in ecosystems.
Abstract Predator induced trait mediated indirect interactions (TMIIs) are likely the dominant fa... more Abstract Predator induced trait mediated indirect interactions (TMIIs) are likely the dominant facet of trophic interactions in aboveground food-webs. New research is beginning to show that TMIIs are also important in revealing how soil food-webs (SFWs) regulate biogeochemical processes. We suggest that TMIIs can modify SFW functions by (a) regulating the quantity and nutritional quality of plants and animal production known to drive the SFW, (b) inducing defense phenotypes in soil-organisms, and (c) changing soil environmental conditions. Currently, very few studies have explored the role TMIIs play in shaping SFW functions, especially the cascading effects on SFW dynamics. Much theoretical and empirical research is needed before we can successfully incorporate the non-consumptive effects of predation into SFW models.
Summary Understanding the ecological function of an animal's pigmentation pattern is an intri... more Summary Understanding the ecological function of an animal's pigmentation pattern is an intriguing research challenge. We used quantitative information on lizard foraging behaviour to search for movement correlates of patterns across taxa. We hypothesized that noticeable longitudinal stripes that enhance escape by motion dazzle are advantageous for mobile foragers that are highly detectable against the stationary background. Cryptic pigmentation patterns are beneficial for less-mobile foragers that rely on camouflage to reduce predation. Using an extensive literature survey and phylogenetically controlled analyses, we found that striped lizards were substantially more mobile than lizards with cryptic patterns. The percentage of time spent moving was the major behavioural index responsible for this difference. We provide empirical support for the hypothesized association between lizard dorsal pigmentation patterns and foraging behaviour. Our simple yet comprehensive explanation may be relevant to many other taxa that present variation in body pigmentation patterns.
Background/Question/Methods The process of energy and materials transfer governs ecosystem produc... more Background/Question/Methods The process of energy and materials transfer governs ecosystem production, food chain length and species diversity. Herbivores are pivotal in this process because their low plant assimilation efficiencies constrain transfer rates and ecosystem carbon: nitrogen balance. Theory suggests that physiological stress due to predation risk could be an important determinant of trophic transfer efficiency and ecosystem nutrient budget. We tested this assertion in a series of field and laboratory experiments. We reared grasshopper herbivore nymphs with or without risk of spider predation and measured their metabolic rate, nutritional requirements, and excretion and body elemental composition. We also calculated how the risk of spider predation affects elemental composition of uneaten plant material entering the soil organic matter pool. Results/Conclusions We show that shifting nutrient demand of herbivores facing predation risk causes carbohydrate carbon to become ...
Background/Question/Methods The physiological reaction of prey to predation involves allocating r... more Background/Question/Methods The physiological reaction of prey to predation involves allocating resources from production to support emergency functions. An example of such a reaction is an increase in maintenance respiration concomitant with higher carbohydrate and lower N demand. Such changes in prey energy and elemental budget should alter the role prey play in regulating the quality of detrital inputs to soils. Nutrient content of detritus is an important determinant of the way soil communities regulate ecosystem processes. Thus, the physiological reaction of prey to predation can potentially explicate changes in ecosystem functioning. Results/Conclusions First empirical examination using an old-field model food-chain of an herbivore grasshopper (prey) and a predatory spider, thus far, support this new conceptual framework. Grasshoppers stressed by spider predators prefer to eat more carbohydrates and have a higher body carbon-to-nitrogen ratio than do grasshoppers raised withou...
The concentration of 11 trace elements (Mg, Al, Mn, Cu, Zn, Rb, Mo, Cd, Ba, Hg and Pb) and sulfur... more The concentration of 11 trace elements (Mg, Al, Mn, Cu, Zn, Rb, Mo, Cd, Ba, Hg and Pb) and sulfur in feathers of pigeons and ravens was determined by ICPMS after wet digestion of the sample. Pigeon feathers were collected from five habitats: rural, industrial, urban, natural ...
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