Presence Of Prey Research Articles

The occurrence of rare corsac fox (Vulpes corsac) in Iran is mainly determined by prey presence and land use

Many species occur on unprotected lands, but continuing human pressure makes them rare especially outside protected areas (PAs). The corsac fox is a common predator in Central Asia, but rare in Iran and its conservation status is poorly understood. We aimed to assess its distribution in relation to natural and human factors. Using 31 occurrence records of corsac and 272 of its main prey species, we used maximum entropy modeling to determine the key factors affecting corsac distribution, find priority conservation areas and evaluate the role of PAs. We found that corsac presence was strongly inversely associated with the distance to gerbil burrows, land use and distance to PA, followed by precipitation, vegetation types, distance to villages, road density and distance to river. Corsacs mostly occurred outside PAs, with highly suitable habitats covering only 6.3% of the study area and one PA covering 11% of highly suitable habitats. Our results suggest that, in Iran, the corsac may tolerate some landscape modification, but its distribution is strongly related to its main prey and low intensity of land use. We suggest to expand the existing no-hunting areas (unclassified by the IUCN) and upgrade them to better managed PAs compliant with international standards.

Plasticity and Multiplicity of Trophic Modes in the Dinoflagellate Karlodinium and Their Pertinence to Population Maintenance and Bloom Dynamics

As the number of mixotrophic protists has been increasingly documented, “mixoplankton”, a third category separated from the traditional categorization of plankton into “phytoplankton” and “zooplankton”, has become a new paradigm and research hotspot in aquatic plankton ecology. While species of dinoflagellates are a dominant group among all recorded members of mixoplankton, the trophic modes of Karlodinium, a genus constituted of cosmopolitan toxic species, were reviewed due to their representative features as mixoplankton and harmful algal blooms (HABs)-causing dinoflagellates. Among at least 15 reported species in the genus, three have been intensively studied for their trophic modes, and all found to be phagotrophic. Their phagotrophy exhibits multiple characteristics: (1) omnivority, i.e., they can ingest a variety of preys in many forms; (2) flexibility in phagotrophic mechanisms, i.e., they can ingest small preys by direct engulfment and much bigger preys by myzocytosis using a peduncle; (3) cannibalism, i.e., species including at least K. veneficum can ingest the dead cells of their own species. However, for some recently described and barely studied species, their tropical modes still need to be investigated further regarding all of the above-mentioned aspects. Mixotrophy of Karlodinium plays a significant role in the population dynamics and the formation of HABs in many ways, which thus deserves further investigation in the aspects of physiological ecology, environmental triggers (e.g., levels of inorganic nutrients and/or presence of preys), energetics, molecular (genes and gene expression regulations) and biochemical (e.g., relevant enzymes and signal molecules) bases, origins, and evaluation of the advantages of being a phagotroph.

Design of experimental food patches to measure foraging intensity for octopus: a case study with the giant Pacific octopusEnteroctopus dofleini

ABSTRACTIn a study of the foraging behaviour of the giant Pacific octopus Enteroctopus dofleini, we designed two types of experimental food patches to measure habitat preferences and perceptions of predation risk. The first patch successfully measured giving-up densities (GUDs), confirmed by octopus prey presence and higher foraging at sites with historically greater octopus presence. However, nontarget foragers also foraged on these experimental food patches. Our second floating patch design successfully excluded nontarget species from subtidal patches, and from intertidal patches at high tide, but allowed for foraging by E. dofleini. The second design successfully measured GUDs and suggested that octopus preferred foraging in a subtidal habitat compared to an intertidal habitat. We ascribe the higher GUD in the intertidal habitat to its higher predation risk relative to the subtidal habitat. The second patch design seems well suited for E. dofleini and, in conjunction with a camera system, could be used to provide behavioural indicators of the octopus's abundance, perceptions of habitat quality and predation risk.

Alternative prey influence the predation of mosquito larvae by three water bug species (Heteroptera: Nepidae)

Abstract The indirect interactions among multiple prey sharing a common predator characterize apparent competition. In conservation biological control involving mosquitoes and controphic prey against generalist insect predators, apparent competition may be a crucial factor determining the extent of success. The possible influence of apparent competition on mosquito prey consumption by three water bugs (Heteroptera: Nepidae): Ranatra elongata, Ranatra filiformis, and Laccotrephes griseus was assessed under laboratory conditions. Tadpoles (Duttaphrynus melanostictus), chironomid larvae, snails (Racesina luteola) and fish fingerlings (Labeo rohita) were considered as alternative prey under two prey or multi prey conditions against instar IV larvae of Culex quinquefasciatus as target prey. Under two prey conditions all the predators exhibited a preference (significant Manly’s α) for mosquito larvae, against fish fingerlings by R. filiformis. In the presence of multiple prey, mosquito larvae were selected by the predators. Using the ratio of mosquito selectivity in two prey and multi-prey conditions as a measure of apparent competition, chironomid larvae had greatest effect in suppressing mosquito selectivity for R. elongata, and fish fingerlings for R. filiformis and L. griseus. It seems that the prey preference of R. elongata, R. filiformis and L. griseus may differentially evoke apparent competition among the prey. In the aquatic community where these predators and prey coexist, mosquito larvae may benefit from apparent competition that reduces their vulnerability to predators. The identity of the alternative prey appears to be an important factor for shielding the vulnerability of mosquito prey to the generalist insect predators.

Alternative extraguild prey modifies focal extraguild prey consumption and parasitism but not intraguild predation intensity

Intraguild predation (IGP) refers to the predation of species that use similar resources and are, therefore, potential competitors. The consuming predator is known as the intraguild predator (IG-predator) and the predator or parasitoid being consumed as the intraguild prey (IG-prey). Prey belonging to another guild are known as extraguild prey (EG-prey). Within a single prey-predator framework, the presence of an alternative prey can reduce the predation rate of a focal prey. However, such an effect has not been studied in an IGP framework. In addition, most studies conducted to analyze IGP intensity (i.e., the level of consumption of the IG-prey) have focused on the influence of a single focal EG-prey but not on the effect of an alternative EG-prey. Therefore, in an IGP framework, we aimed to assess how the presence of an alternative EG-prey could affect the predation and parasitism rates of a focal EG-prey, as well as IGP intensity. On the basis of intrinsic characteristics of the IG-predator and current literature, we hypothesized that the presence of the alternative EG-prey would reduce predation and parasitism of the focal EG-prey as well as IGP intensity. Our results showed that, as expected, the presence of an alternative EG-prey reduces the predation rate of the focal EG-prey when both the IG-predator and the IG-prey are released concomitantly, but not when the IG-predator is released sequentially. In addition, contrary to our expectations, the presence of an alternative EG-prey did not reduce the intensity of IGP, indicating that besides intrinsic characteristics of the IG-predators, other factors may be important mediators of IGP intensity. Potential implications of these findings are discussed under a biological control perspective.

Inducible morphological defense in Daphnia pulex: food quantity effects revised

In aquatic systems, organisms largely rely on chemical cues to perceive information about the presence of predators or prey. Daphnia recognize the presence of the predatory larvae of Chaoborus via a chemical cue, emitted by the larvae, a so-called kairomone. Upon recognition, neckteeth, an alteration of the carapace, are induced in Daphnia that reduce predation rates of Chaoborus. Neckteeth induction was often reported to entail costs. In a previous study, food quantity affected the level of neckteeth induction, with stronger neckteeth induction at low food concentrations and weak induction at high food concentrations. However, reducing neckteeth induction at high food quantities seems to be maladaptive and not in accordance with the concept that inducible defenses are associated with costs.Here, we hypothesized that weaker neckteeth induction at high food concentrations is caused by increased bacterial degradation of the kairomone. More specifically, we assume that higher algal food concentration is associated with higher bacterial abundances, which degrade the kairomone during the experiment. We tested our hypothesis by treating food algae with antibiotics before providing them as food to Daphnia. Antibiotics reduced bacterial abundances at high and low food concentrations. Reduced bacterial abundances at high food concentrations led to the same level of neckteeth induction as at low food concentrations. A linear regression revealed a significant correlation of neckteeth induction to bacterial abundances. We therefore conclude that differences in neckteeth induction at different food concentrations are not caused by the food quantity effects but by differences in bacterial degradation of the kairomone.

Expression of Genes Involved in Offensive and Defensive Phenotype Induction in the Pituitary Gland of the Hokkaido Salamander (Hynobius retardatus).

Amphibians exhibit phenotypic plasticity, which allows flexible adaptation to fluctuating environments. Although genes involved in expression of plastic phenotypes have been identified, the endocrine bases of plastic responses are largely unknown. Larvae of the Hokkaido salamander (Hynobius retardatus) plastically display distinct phenotypes, an "offensive phenotype" characterized as larger body with broadened gape and a "defensive phenotype" characterized as enlarged gills and tail and less active behavior, in the presence of prey larval amphibians and predatory larval dragonfly, respectively. In the presence of both prey and predators, the degree of induction of both phenotypes is reduced, suggesting cross-talk between the molecular signaling pathways of these phenotypes. We conducted a transcriptomic analysis to examine how endocrine regulation affects the phenotypic expression by focusing on the pituitary gland. We found that five endocrine genes, i.e., calcitonin related polypeptide alpha (CALCA), growth hormone (GH), neuropeptide B (NPB), parathyroid hormone 2 (PTH2), and prolactin 1 (PRL1), were involved in the expression of both phenotypes. However, we conducted only RNA-seq analysis, and no confirmation of significant up-regulation or down-regulation has been conducted. These results suggest that these genes were up-regulated for induction of the offensive phenotype and down-regulated for induction of the defensive phenotype. Phylogenetic analysis indicated that possible gene duplications of PRL and CALCA have occurred during amphibian evolution. Based on these findings, it is suggested that a trade-off of molecular signaling pathways exists between the two distinct phenotypic expressions. The results also suggest that hormonal-gene duplications might have contributed to the acquisition of phenotypic plasticity in amphibians.

Every hill has its leopard: patterns of space use by leopards (Panthera pardus) in a mixed use landscape in India.

Understanding abundance and distribution of species is often necessary for wildlife conservation. However, elusive species such as the leopard (Panthera pardus) that have wide geographical distribution and typically low abundance pose a constant challenge to conservationists due to logistical and methodological constraints. Although leopard abundance has been estimated at the scale of protected areas or other smaller regions, reliable information describing leopard distribution over large spatial scales remains largely unavailable. Knowledge about space use by leopards within landscapes could help improve conservation management, reduce human-wildlife conflict, and also facilitate population status monitoring. We carried out occupancy surveys across c. 24,000 km2 in southern India in a landscape that consisted a mosaic of leopards’ natural habitats and highly human-dominated areas. We investigated the effects of key ecological and anthropogenic variables in determining leopard space use patterns. We addressed imperfect detections obtained using sign surveys conducted on spatially replicated transects within sampling units by modeling detection as a function of spatial auto-correlation and covariates. Our results show that the probability of site-use by leopards across the landscape varied between 0.02 (95% CI [0.01–0.09]) and 0.99 (95% CI [0.99–1.0]) across the study area. The best model (AIC weight = 0.97) showed that the probability of leopard space use was affected by the proportion of natural habitats and the presence of large wild prey in the sampling unit. Given that India is undergoing rapid modifications due to economic changes and demand for natural resources, we emphasize the need for landscape-based approach for conserving and monitoring leopards. We argue that leopards are an indicator of functional ecosystems represented by scrub, deciduous forest and rocky outcrops that do not always get prioritized for conservation, unlike densely forested habitats. Similarly, conservation of natural large wild prey, especially outside the protected area system, should assume greater importance, which could also have a positive impact on reducing human-leopard conflict.

Changes in positive associations among vertebrate predators at South Georgia during winter

We studied positive associations among seabirds and marine mammals at South Georgia on research cruises during the Austral winters of 1985, 1991 and 1993 and found statistically significant differences. We collected data on abundance and distribution, providing a critical reference for sub-Antarctic conservation in anticipation of future environmental changes. We found significant changes in the abundance of 29% of species surveyed and a consequent change in species diversity. We postulate that the resulting altered community composition may have previously unanticipated population effects on the component species, due to changes in positive interactions among species which use each other as cues to the presence of prey. We found a near threefold reduction in spatial overlap among vertebrate predators, associated with warming sea temperatures. As the strength and opportunity for positive associations decreases in the future, feeding success may be negatively impacted. In this way, environmental changes may disproportionately impact predator abundances and such changes are likely already underway, as Southern Ocean temperatures have increased substantially since our surveys. Of course the changes we describe are not solely due to changing sea temperature or any other single cause—many factors are important and we do not claim to have removed these from consideration. Rather, we report previously undocumented changes in positive associations among species, and argue these changes may continue into the future, given near-certain continued increases in climate-related changes.

Ecological implications of unprecedented warm water anomalies on interannual prey preferences and foraging areas of Guadalupe fur seals

AbstractThe Guadalupe fur seal (GFS) currently is recovering from near extinction and prey availability is an important factor. Scat and stable isotope analyses (SIA) were used to assess GFS foraging on Guadalupe Island during 2013–2016. This period was characterized by normal (2013) ocean temperatures followed by warm conditions (2014–2016). Scat samples (~40/year) were collected for prey identification. Additionally, lanugo samples from 1‐month‐old pups (50/year) were processed for SIA (δ13C/δ15N). Interannual prey preferences were identified (ANOSIM,p < .05), including significant differences between 2013 and the anomalous years. The most important prey species among these years was the jumbo squid; followed by the neon flying squid (2014–2016). The GFS diet was more specialized in 2013–2015 and more generalized in 2016. Prey from higher trophic levels (determined by scat analysis) were consumed during 2014–2016, but with significantly lower δ13C/δ15N values than in 2013 (ANOVA,p < .05 for both isotope ratios). This pattern may indicate more northerly or offshore foraging areas, with the presence of oceanic prey (neon flying squid). The widest isotopic niche was observed in 2015 (2.2‰2), reflecting a broader foraging area. Our findings are an important step toward better understanding the impacts of climate change on the recovery of GFS.

Surrounding landscape influences the abundance of insect predators in rice field

BackgroundNatural enemy abundance in a crop plot depends on its prey presence and also influenced by habitats close to field. Landscape changes are also important factors driving pest and natural enemy population abundance in a specific crop field. Examining these kinds of effects on insect pests or biocontrol agents, as well as analysis of their functional food webs, would be asset to make a fruitful pest management programme at local scales. Therefore, this study was undertaken to evaluate the impact of surrounding landscape on the abundance insect predators in rice field.ResultsThis study revealed a dependency on rice bund margin width, with spider populations increasing with increased bund widths. Conversely, population abundance did not rely on the number of weed species observed on earthen ridge around the rice field. In general, relative abundances of predator populations differed significantly across the three landscapes tested. Among the four predators of rice insect pest, the green mirid bug showed highest number irrespective of landscape. Comparatively, higher predator diversity (Shanon diversity) was observed in landscape I followed by landscape III and landscape II. All landscapes showed different diversity indices indicating heterozygosity existed in each study site. These landscape diversity influences the predator’s abundances at a local scale. Variogram derived from this study also indicated the landscape heterozygosity existed in studied locations which can also explain the predator’s abundances in rice field at locale scale.ConclusionThese findings suggest that predators of rice insect pests are landscape specific. Therefore, characterization of each local landscape in Bangladesh rice production landscapes are necessary before planning and implementation of integrated pest management. Geospatial analysis of local landscape would be more effective to analyze such unique characteristics. As a step in this direction, preliminary variography analyses using the RED spectral band of December 2016 LANDSAT 8 imagery propose an initial learning suite of methods for describing useful local characteristics affecting rice pest predators.

Vegetación y estructura del hábitat que determina la dieta de aves insectívoras en sistemas agroforestales

Para definir la vegetación y estructura del hábitat con relación a la presencia de aves y presas de agosto 2018 a enero 2019 se llevó acabo el seguimiento de aves, vegetación e insectos, empleando recuento en puntos con radio fijo; búsqueda intensiva; corte y sacudida de ramas, líneas de Canfield, cuadrantes con punto central y el vecino más cercano. Se determinó frecuencia de observación (FO) e índice de abundancia relativa (IAR). Para determinar diferencias y conocer si lo registrado es lo esperado se desarrollaron análisis de kruskal wallis y X2. Para evaluar asociación entre el hábitat y vegetación en relación con la presencia de aves e insectos se aplicó un análisis de regresión Poisson (ARP). Para conocer el grado de inercia entre hábitat y vegetación en respuesta a la presencia de aves e insectos se desarrollaron análisis de correspondencia canónica (ACC). La FO señala valores altos para: Aves Melanerpes aurifrons, Cyanocorax morio y Empidonax sp.; vegetación Poaceae, Selaginellaceae y Verbenaceae; insectos Plecia nearctica y Chauliognathus pensylvanicus. El IAR señala valores altos para: vegetación Poaceae, Selaginellaceae y Verbenaceae; insectos Plecia nearctica y Chauliognathus pensylvanicus. Kruskal wallis sin diferencias y X2 que lo registrado es lo esperado. El ARP sugiere un AIC= 283.65; 219.4; 240.38. El ACC evidencia una inercia de: 66.26%; 78.54%; 93.89% y 84.62%. La vegetación y estructura del hábitat son factores determinantes en la abundancia de aves, disponen del stock alimenticio que garantiza la conservación y equilibrio ecológico de los sistemas agroforestales.

Socially foraging bats discriminate between group members based on search-phase echolocation calls

Abstract Animals have evolved diverse strategies to use social information for increasing foraging success and efficiency. Echolocating bats, for example, can eavesdrop on bats foraging nearby because they shift from search-phase calls to feeding buzzes when they detect prey. Feeding buzzes can directly convey information about prey presence, but it is unknown whether search-phase calls also convey social information. Here, we investigated whether search-phase echolocation calls, distinct calls produced by some bat species to scan large open areas for prey, can additionally convey individual identity. We tested this in Molossus molossus, a neotropical insectivorous bat that forages with group members, presumably to find ephemeral insect swarms more efficiently. We caught M. molossus from six different social groups and recorded their search-phase calls during a standardized release procedure, then recaptured and tested 19 marked bats with habituation–dishabituation playback experiments. We showed that they can discriminate between group members based on search-phase calls, and our statistical analysis of call parameters supported the presence of individual signatures in search-phase calls. Individual discrimination is a prerequisite of individual recognition, which may allow M. molossus to maintain contact with group members while foraging without using specialized signals for communication.

<p><strong>Extraguild prey availability reduced cannibalism and reciprocal intraguild predation of </strong><strong><em>Neoseiulus barkeri</em></strong><strong> (Acari: Phytoseiidae) and </strong><strong><em>Scolothrips takahashii</em></strong><strong> (Thysanoptera: Thripidae)</strong><strong></strong></p>

Cannibalism and intraguild predation (IGP) are two common interactions occurs in animal kingdom which influence their population structure and dynamics. Neoseiulus barkeri (Hughes) and Scolothrips takahashii (Priesner) are important natural enemies of citrus red mite Panonychus citri (McGregor). However, little was known about their interactions and how the availability of extraguild (EG) prey P. citri modulated their interactions. In this study, we determined incidences of cannibalism and intraguild predation of these two predators when different densities of extraguild prey P. citri were available. Our results showed that incidences of both cannibalism and IGP and were significantly reduced in the presence of the extraguild prey. The intraguild predation between N. barkeri and S. takahashii was bidirectional, but N. barkeri was a predominant intraguild predator over S. takahashii. The S. takahashii fed on immobile N. barkeri egg, and N. barkeri fed on inactive prepupa and pupa of S. takahashii, but the conspecifics seldom did. Our results indicated that the interactions of predators decreased significantly when prey was available. The predatory mite N. barkeri was a stronger interspecific competitor. The results of this study may be useful in developing effective biological control strategies against P. citri.

Polymerase chain reaction as a promising tool for DNA-based diet studies of crustaceans

Studying the diet of crustaceans based on the direct visual inspection of the gut contents can be difficult because they can ingest only a portion of the prey and further crush it into very small pieces, making a very few food items identifiable. Here, the usefulness of molecular methods to identify the species present in the gut contents of two crustaceans, the shore crab Carcinus maenas and the brown shrimp Crangon crangon, was tested. Stomach contents were removed, and their total genomic DNA extracted followed by amplification (PCR) with four specific prey mtDNA primers. Since both crustaceans are opportunistic predators, preying upon around 40 different species, the study was restricted to common potential preys in the sampled area, the Minho Estuary (Portugal): the common goby Pomatoschistus microps, the ragworm Hediste diversicolor, the flounder Platichthys flesus and the peppery furrow shell Scrobicularia plana. After testing the most appropriate methodology for DNA extraction and PCR amplification to detect the presence of each potential prey with positive control samples, the same methodology was applied to the stomach content samples. The molecular methods allowed for detection of the presence of P. microps, P. flesus and H. diversicolor in the stomachs of both crustaceans. Therefore, once potential prey and their availability in the system are known, PCR technique can be an alternative tool to overcome some of the limitations of traditional methods in the study of the crustaceans’ diet, even when stomach contents include a great part of ‘detritus’. This study reflects also the need to develop more tools (primers) to improve the assessment of predator–prey interactions in aquatic ecosytems.

Cyclopoids feed selectively on free‐living stages of parasites

Abstract Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free‐living stages (cercariae) when an alternative food source is present. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind−1 hr−1 and 17 ciliate ind−1 hr−1. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

Enhanced recruitment of larger predators in the presence of large prey.

Most carnivores undergo diet shift from smaller to larger prey items during ontogeny. The trophic relationship between a growing carnivore and larger prey is representative of a size-structured predator-prey interaction. The strength of this interaction is, in part, determined by the recruitment of individuals from smaller predatory size classes into larger predatory size classes. Therefore, it is interesting to investigate how larger prey alter the recruitment of smaller predator size classes into larger predator size classes, since this can affect their own future predation risk. Past empirical studies have exclusively documented that large prey reduce predator recruitment by decreasing growth and/or survival of the smaller predators. In this study, we provide empirical evidence of the contrasting pattern: large prey enhance the recruitment of smaller predators into larger predators even though they increase cannibalism mortality of the smaller predators. We have done this here by studying the trophic interaction between predatory salamander larvae Hynobius retardatus and the frog tadpoles Rana pirica that represent their large prey. In a field experiment in which salamander hatchlings were exposed to the presence or absence of large frog tadpoles, we found that more giant salamanders emerged in the presence of frog tadpoles than in their absence. Reassignment of frog tadpoles (to both treatments) in the subsequent experimental period showed that the enhanced emergence of giant salamanders in the presence of frog tadpoles leads to the intensification of salamander predation on the frog tadpoles. In an additional laboratory experiment, to better understand the underlying mechanisms, we manipulated both the presence of frog tadpoles and the occurrence of cannibalism between salamander hatchlings. This experiment revealed that frog tadpoles intensify the cannibalism of salamander larvae during their hatchling stage, thus allowing more salamander larvae to become large-sized predators. Our results suggest that frog tadpoles can inadvertently intensify their own future predation risk by intensifying cannibalistic interactions among predatory salamander hatchlings, thereby enhancing the degree of predator recruitment to a larger size class. Hence, large prey can enhance the recruitment of individuals from small predator size classes into larger predator size classes.

Diet and Feeding Ecology of Crotalus tzabcan (Serpentes: Viperidae)

The Tzabcan rattlesnake (Crotalus tzabcan) is endemic to the Yucatan Peninsula and is part of the C. durissus complex. Although relatively widespread, it is rather an uncommon species; therefore, little is known about its natural history. Herein, we describe the diet of C. tzabcan on the basis of data from field encounters, museum specimens, and published data. Dietary samples were collected from Campeche, Quintana Roo, and Yucatan, Mexico, and literature records from Belize, representing most of the species' distribution range. Examination of 50 individuals resulted in 28 prey items obtained from 27 snakes. The diet of C. tzabcan consisted exclusively of mammals, including the orders Rodentia (86% of the prey items) and Soricomorpha (7%), and no ontogenetic shift in prey type was detected. However, an ontogenetic telescope is evident, where adults consume larger prey than juveniles but continue feeding on small prey. No sexual dimorphism in snout–vent length and total length was detected in C. tzabcan. No sexual differences in prey mass were found when controlling for snake body length, nor when comparing between sexes in adults and juveniles. The presence of prey was not related to snake collection date, suggesting year-round feeding. There was no difference in prey class and size among snakes from Yucatan dry forest and moist forest. These results suggest a homogenous diet among sexes, seasons, and populations. This is the first detailed study on the diet and feeding ecology of C. tzabcan, and it adds five new prey species: Cryptotys mayensis, Heteromys desmarestianus, H. gaumeri, Oryzomys couesi, and Rattus rattus, as well as two previously reported ones: Mus musculus and Sigmodon toltecus. These findings contrast with anecdotal reports of C. tzabcan consuming reptiles and birds and show many similarities with the related species C. durissus. Additional studies on the natural history of C. tzabcan and related species would help to better understand how the feeding ecology of Neotropical rattlesnakes differs from those species of temperate zones.

Potential functional and numerical response in a large sized raptor may be mediated by the abundance of an exotic lagomorph

Predators relying on a particular prey as their main food resource are especially susceptible to fluctuation in prey availability. When prey abundance decreases they show a functional response by adjusting their diet. After this, predators may suffer a numerical response. These responses have been poorly studied in presence of alien invasive preys. The black-chested buzzard-eagle (Geranoaetus melanoleucus) is a large raptor inhabiting open areas of South America. Here we present the first long-term study on this eagle population tendency, analyzing functional and numerical responses associated with changes in the abundance of the exotic European hare (Lepus europaeus). We measured breeding performance and studied eagles’ diet during the breeding seasons of 1991, 1992, 2006, 2011 and 2012. We also estimated the relative abundance of hares in those years. Eagles diets changed over the years with a decrease in hare consumption. The number of eagles decreased from 1992 to less than half in 2012. Forty one percent of the total eagles observed in 1991/92, and 27% in 2006 were immature, while in 2011 and 2012 no immature were observed. We found similar tendencies of decrease in the abundance of hares which suggest that the decrease in eagles population may be related with the decreasing tendency of hares. No other factor that may have affected immature eagles abundance was evident in the area during this period. Our data suggest that changes in the abundance of an exotic lagomorph may lead numerical and functional responses in a top predator by affecting its diet, age structure, and ultimately abundance.

The Importance of Sounds to Fishes

Fishes can detect underwater sounds and use them to obtain key information about the environment around them. Sounds travel rapidly over great distances in water and can provide detailed information on the presence of prey, predators, and related fishes, while the overall acoustic scene provides the fishes with key information about their environment. Although they do not have the external ears that many vertebrates have, all fish species have effective internal ears. Many fish species engage in making sounds themselves. Their calls are often produced when they are approached by other fish species, and they can be used to startle and deflect their opponents. Sounds are also produced during reproductive activities. There are often differences in the sounds made by fish species, even between closely related species. The sounds of individuals may also differ, and this may play a role in sexual selection, as males compete with one another and aim to attract females that are looking for the best males to mate with. The sounds that fishes can hear are confined to low frequencies, although this is species- dependent. It is evident that fishes can distinguish between sounds that differ in their amplitude and frequency, and also discriminate between sounds that have different temporal characteristics. They can also distinguish between sounds that arrive from different directions and distances, in some cases enabling them to locate the sources of sound. Detecting sounds may enable fishes to navigate and move to particular habitats, search for prey, move away from predators, and communicate during spawning. However, a particular problem in sound detection is the masking of those sounds that interest the fishes by high and variable levels of background noise. Although some of the background noise is generated by natural sources, including the precipitation of rain and snow, and wind and waves, many underwater sounds now come from anthropogenic sources. Some of these human-made sounds can kill or injure fishes, impair their hearing, and alter their behaviour. Interference with the detection of sounds can have especially adverse effects upon the lives of fishes. There is a need for more work on the impact of human- made underwater noise upon the fitness of fishes, and the strength of fish populations.