Ecophysiology of the kleptoplastidic dinoflagellate Shimiella gracilenta: I. spatiotemporal distribution in Korean coastal waters and growth and ingestion rates

To explore the ecophysiological characteristics of the kleptoplastidic dinoflagellate Shimiella gracilenta, we determined its spatiotemporal distribution in Korean coastal waters and growth and ingestion rates as a function of prey concentration. The abundance of S. gracilenta at 28 stations from 2015 to 2018 was measured using quantitative realtime polymerase chain reaction. Cells of S. gracilenta were detected at least once at all the stations and in each season, when temperature and salinity were 1.7–26.4°C and 9.9–35.6, respectively. Moreover, among the 28 potential prey species tested, S. gracilenta SGJH1904 fed on diverse prey taxa. However, the highest abundance of S. gracilenta was only 3 cells mL-1 during the study period. The threshold Teleaulax amphioxeia concentration for S. gracilenta growth was 5,618 cells mL-1, which was much higher than the highest abundance of T. amphioxeia (667 cells mL-1). Thus, T. amphioxeia was not likely to support the growth of S. gracilenta in the field during the study period. However, the maximum specific growth and ingestion rates of S. gracilenta on T. amphioxeia, the optimal prey species, were 1.36 d-1 and 0.04 ng C predator- 1 d-1, respectively. Thus, if the abundance of T. amphioxeia was much higher than 5,618 cells mL-1, the abundance of S. gracilenta could be much higher than the highest abundance observed in this study. Eurythermal and euryhaline characteristics of S. gracilenta and its ability to feed on diverse prey species and conduct kleptoplastidy are likely to be responsible for its common spatiotemporal distribution.

Living with the enemy: activity rhythms of the red fox and some potential preys in an urban environment

The present study aimed at investigating the activity rhythms of the red fox Vulpes vulpes and three potential preys (i.e. the European hedgehog Erinaceus europaeus, the wood mouse Apodemus sylvaticus, and the Norway rat Rattus norvegicus) in an urban environment. Data were collected as a part of a camera trapping survey, carried out within the municipality of Padua (northeastern Italy). In order to analyse species activity patterns, the R overlap package was used and then the Watson-Wheeler test was run to evaluate whether two overlaps were significantly different. Results show that all the investigated species have nocturnal activities, with “moderate” temporal activity overlap between the red fox and its potential prey. The Watson-Wheeler test showed that the hedgehog was the only potential prey that did not show significant differences in the hours of activity compared to those of the red fox. Instead, statistically significant differences were recorded when the activity rhythm of the red fox was compared with that of the wood mouse or the Norway rat. This may indicate the development of antipredator behaviour or the possibility that the red fox is seeking anthropogenic food sources instead of wild prey or, alternatively, other preferred food items.

First evidence of hunting of a Crested Indian Porcupine by an avian predator: The Eurasian Eagle Owl

Encounters between birds of prey and porcupines are rarely documented, and so far only in North America. At least 39% of such encounters lead to death of the attacker. We present first evidence for similar encounters between The Eurasian Eagle Owl and the Indian Crested Porcupine, suggesting that young porcupines may occasionally serve as potential prey for the owl.

Camera trap based niche partitioning model of medium size ungulates and its implications on tigers prey availability in SE Asian rainforest

The presence and survival of the Sumatran tiger were determined by the presence, density, and activity of its prey. Several medium size mammal belongs to the ungulate were known as the potential prey for the tiger. While, the information on the temporal availability of this prey in the rainforest is still limited. In here this study aimed to aims to model the niche partitioning of several mammalian species that was potential prey for tiger. The studied species were including barking deer (Muntiacus muntjak), bearded pig (Sus barbatus), and wild boar (Sus scrofa). The method was using camera trap with data analyses including the calculation of Kernel density, diel activity, and niche partitioning determined using overlap index. Based on the results, barking deer and wild boar showed only singular activity peak while bearded pig has several activity peaks. Only wild boar showed a strict diurnal activity pattern between 06:00 h and 12:00 h. Barking deer showed a crepuscular behavior with several activities observed at 18:00 h. While bearded pig showed a nocturnal behavior and showed at least two peaks of activity, one between 09:00 to 13:00 and another between 18:00 to 24:00 h. Barking deer and bearded pig uses almost similar niches since those species have the highest overlap indices value equals 0.504(95%CI:0.193-0.824). The lowest overlap indices value was observed for barking deer and wild boar with overlap indice values of 0.032(95%CI:0.0-0.162). Considering the diurnal activity pattern of the tiger that is mostly active at day, then the available preys were either barking deer or bearded pigs. While since barking deer and bearded pigs were using the same niche, then there will be potential competition.

Daily activity pattern of pumas (Puma concolor) and their potential prey in a tropical cloud forest of Colombia

Ecosystems in the northern Andes face unprecedented habitat loss. Pumas are the top predators in the region and exert key ecological functions, such as population control and resource facilitation. However, little is known about the temporal niche of the species or its effects on behaviour of prey in the tropics. We hypothesized that there is a link between the activity patterns of pumas and their prey in a cloud forest of the Central Andes of Colombia. We installed 61 camera traps to estimate the degree of overlap between the daily activity curves of pumas and seven potential prey species, using conditional kernel density functions. Pumas, armadillos, mountain pacas, and white–eared opossums were mainly nocturnal, with little crepuscular activity and high temporal overlap. Central American agouti, mountain coati, little red brocket deer, and Cauca guan displayed a predominantly diurnal activity and temporal partitioning with pumas. As opportunistic predators, pumas were able to maximize foraging efficiency by preying on the crepuscular and nocturnal species. Conservation of this highland predator will largely depend on the suitable management of its native prey.

Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider

In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic bird droppings in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders, therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among bird droppings, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans in particular were attracted to bird droppings at a higher rate than to spiders, other dipterans and hymenopterans were attracted to bird droppings at a similar rate as spiders. Both spiders and bird droppings attracted insects at a significantly higher rate than did control leaves. As predicted, prey were attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and bird droppings can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as bird droppings, and bird dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.

Theropod guild structure and the tyrannosaurid niche assimilation hypothesis: implications for predatory dinosaur macroecology and ontogeny in later Late Cretaceous Asiamerica

Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult medium-sized (50–500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with “missing middle-sized” predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The “missing middle-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the niches previously occupied by mid-sized theropod predators, we would expect the evolution of distinct transitions in morphology and possibly the delay of the achievement of somatic maturity in species of this taxon.

Feeding Ecology of Elusive Caribbean Killer Whales Inferred From Bayesian Stable Isotope Mixing Models and Whalers’ Ecological Knowledge

Investigating the feeding ecology of marine predators is critical for understanding their roles and functional importance in ecosystems. However, assessing the diet of large and wide-ranging predators can be challenging, particularly in the case of rare and elusive species. Killer whales (Orcinus orca) are large apex predators in global oceans, but very little is known about their feeding ecology in tropical ecosystems, particularly in the Caribbean Sea. Killer whales are distributed throughout the Caribbean, and are a regular target of artisanal whalers in St. Vincent and the Grenadines (West Indies). Here we investigate the feeding ecology of Caribbean killer whales using a combination of stable isotope analysis (δ15N, δ13C) and traditional ecological knowledge (TEK) data from whalers operating from St. Vincent. Potential prey data from the Caribbean region included large pelagic teleosts, sea turtles, oceanic sharks, cetaceans, and oceanic cephalopods. Mixing models suggest that the contribution of odontocete cetaceans to the diet of killer whales is the most important (overall mean contribution: 60.4%), particularly mesopelagic delphinids (Lagenodelphis hosei; 26.4%, SD = 0.14), large teuthophageous odontocetes (Physeter macrocephalus, Globicephala macrorhynchus; 20.0%, SD = 0.14), and epipelagic delphinids (Stenella attenuata; 14%, SD = 0.14). Oceanic sharks (Carcharhinus longimanus) had a contribution of 17.0% of the diet of killer whales (SD = 0.13), and other potential prey had a relatively marginal contribution. TEK data suggest that whalers believe killer whales feed almost exclusively on cetaceans, particularly odontocete species that they hunt (e.g., G. macrorhynchus). Stable isotope and TEK data were consistent to some extent, although TEK data are qualitative and based on a limited number of observations. Despite some limitations (including sample size for both methods), this study highlights the value of combining independent data sources and methodologies to investigate the ecological roles of marine predators in data-poor regions.

An experimental assessment of social tolerance and den ecology in a high-density octopus population

Long held notions of the universally asocial octopus are being challenged due to the identification of high-density and interacting octopus populations in Australia, Indonesia, Japan and the deep sea. This study experimentally assessed the social tolerance and presence of potential prey items of Caribbean reef octopus, Octopus briareus, in a tropical marine lake (25°21′40″N, 76°30′40″W) on the island of Eleuthera, The Bahamas, by deploying artificial dens in multi-den groups or ‘units’ in the months of May and June 2019. Fifteen octopus were observed occupying dens (n = 100), resulting in 13 den units being occupied (n = 40). Two examples of adjacent occupation within a single den unit were identified but with zero examples of cohabitation/den sharing. Ecological models showed den and den unit occupation was predicted to increase with depth and differ between sites. Octopus also displayed no preference for isolated or communal units but preferred isolated dens over dens adjacent to others. Additionally, 47 % of occupied dens contained bivalve or crustacean items with no epifauna on their interior surface. The lack of epifauna suggests that these items have been recently ‘cleaned’ by occupying octopus and so represent likely prey. This study presents evidence of possible antisocial den use by O. briareus, a modification of the default ‘asocial’ ignoring of conspecifics typically attributed to octopus. This is likely in response to the high population density and may imply behavioural plasticity, making this system appropriate for further scrutiny as a research location on the influence of large, insular environments on marine species.

Hide-and-seek strategies and post-contact immobility

To understand why an animal might gain by playing dead, or more precisely, exhibit post-contact immobility (PCI), we consider the context in which this behaviour occurs. Is it, for example, a method by which a potential victim encourages a predator to direct its attention elsewhere? We investigate this possibility by using the marginal value theorem to analyse predator behaviour in the context of this defence strategy by potential prey. We consider two models. In the first, (random revisiting) the predator may return to sites it has already depleted within the patch. In the second, (systematic search) the predator goes only to new sites within the patch. The results of the two models are qualitatively extremely similar. We show that when prey occur in patches, PCI favours prey survival. Indeed, certain antlion larvae have PCI durations characterized by very long half-lives. These appear to be of such long durations that further increases would convey no substantial benefits in redirecting potential predators to other antlions within the patch and subsequently to other patches.