Combining motility and bioluminescent signalling aids mate finding in deep-sea fish: a simulation study

We present a model to estimate the mean time required for mate finding among deep-sea fish as a function of motility and the extent of bioluminescent signalling. This model differs from those of previous works in 3 important ways by including (1) sex differences in motility, (2) a maximum detection range of bioluminescent signals derived from a recently published mechanistic model based on physical principles and the physiology of vision, and (3) a novel consideration of the likelihood of individuals passing within detection range only in the interval between flashes and hence, failing to detect the signaller. We argue that the flash rates required for effective detection are low, with rates of less than 1 per minute being entirely plausible, and that predation pressure may further encourage low flash rates. Further, even at high flash frequencies, the energetic cost of bioluminescent signalling is argued to be a trivial fraction of resting metabolic rates. Using empirically derived estimates for parameter values, we estimate that a female will be detected and reached by a male within 2 to 4 h of beginning to signal. Hence, we argue that mate finding may not seriously restrict reproductive success in species that can exploit this signalling system. We further argue that where male motility allows bioluminescent signalling, this may have some advantages over chemical-based signalling. Bioluminescent signalling may, therefore, be more important to mate finding in the deep sea (relative to chemical signals) than some previous works have suggested

Consequences of variation in predator attack for the evolution of the selfish herd

There is a strong body of evidence that patterns of collective behaviour in grouping animals are governed by interactions between small numbers of individuals within the group. These findings contrast with study of the ‘selfish herd’, where increasingly complex individual-level movement rules have been proposed to explain the rapid increase in aggregation observed when prey groups are startled by or detect a predator. While individuals using simple rules take into account the position of only a few neighbours, those using complex rules incorporate multiple neighbours, and their relative distance, to determine their movement direction. Here, we simulate the evolution of selfish herd behaviour to assess the conditions under which simple and complex movement rules might evolve, explicitly testing predictions arising from previous work. We find that complex rules outperform simple ones under a range of predator attack strategies, but that simple rules can fix in populations particularly when they are already in the majority, suggesting strong positive frequency dependence in rule success. In addition, we explore whether a movement rule derived from studies of collective behaviour (where individuals use the position of seven neighbours to determine movement direction) performs as successfully as more complex rules, finding again positive frequency dependence in rule success, and a particular role for predator attack strategy (from within or outside the group)

The effect of aggregation on visibility in open water

Aggregation is a common life-history trait in open-water taxa. Qualitative understanding of how aggregation by prey influences their encounter rates with predators is critical for understanding pelagic predator-prey interactions and trophic webs.We extend a recently developed theory on underwater visibility to predict the consequences of grouping in open-water species in terms of increased visual detection of groups by predators. Our model suggests that enhanced visibility will be relatively modest, with maximum detection distance typically only doubling for a 100-fold increase in the number of prey in a group. This result suggests that although larger groups are more easily detected, this cost to aggregation will in many cases be dominated by benefits, especially through risk dilution in situations where predators cannot consume all members of a discovered group. This, in turn, helps to explain the ubiquity of grouping across a great variety of open-water taxa.PostprintPeer reviewe

Four scenarios in which shadow competition should be prominent and factors affecting its strength

Shadow competition is the interception of moving prey by a predator closer to its arrival source, preventing its availability to predators downstream. Shadow competition is likely common in nature, and unlike some other competition types, has a strong spatial component (with the exception of competition for space, which clearly also has a spatial component). We used an individual‐based spatially‐explicit simulation model to examine whether shadow competition takes place and which factors affect it in four scenarios considering ambush predators and active prey. First, when prey capture is uncertain (‘the ricochet effect'). Here, the strength of shadow competition increases when it is harder to capture prey after the first unsuccessful capture attempt, whereas shadow competition is moderated if capture success is higher in successive attempts. Second, shadow competition becomes stronger when predators can capture prey arriving only from certain directions. Third, when prey tend to move along a barrier after encountering it. Here, predators located along this barrier may be more successful than those at random positions, but shadow competition in this scenario drastically decreases the capture success of predators in central positions along a barrier (i.e. having more than a single neighbor). Finally, in three‐level systems of plants in clusters, herbivores searching for plants, and predators ambushing herbivores inside plant patches, predators with ambush locations in the periphery of plant patches are more successful than those at the patch center, especially at high predator densities. Our simulation indicates that shadow competition is plausibly relevant in various scenarios of ambush predators and prey, and that it varies based on the habitat structure and capture probability of prey by predators as well as the change in capture probability with successive encounters.Publisher PDFPeer reviewe

Foraging mode switching : the importance of prey distribution and foraging currency

A.D.H. was supported by the European Research Council (Advanced Grant 250209 to Alasdair Houston), a College for Life Sciences Fellowship at the Wissenschaftskolleg zu Berlin, and a NERC Independent Research FellowshipNE/L011921/1.Foraging methods are highly variable, but can be grouped into two modes: searching and ambush. While research has focused on the functioning of each mode, the question of how animals choose which to use has been largely neglected. Here we consider a forager that exploits prey that are patchily distributed in space and time. This forager can either sit and wait for prey to appear or search for prey, which is more likely to result in encounters with prey but costs more energy and/or exposes the forager to greater predation risk. The currency that natural selection appears to have optimized will be determined by the additional costs of searching and whether there is a risk of starvation. We therefore compare the predictions of models based on currencies that consider only energy and predation risk to state-dependent models in which energy reserves are used to trade off predation rate, starvation rate and investment in growth. The choice of currency qualitatively affects how mode should change when prey abundance and prey patchiness increase. We show how differing prey distributions can explain variation in effects of experimentally increasing prey abundance. Our work has several implications for the study of foraging mode, population dynamics and the methods used to assess population size.Publisher PDFPeer reviewe

A note on the Wilcoxon-Mann-Whitney test and tied observations

Recently, it was recommended to omit tied observations before applying the two-sample Wilcoxon-Mann-Whitney test McGee M. et al. (2018). Using a simulation study, we argue for exact tests using all the data (including tied values) as a preferable approach. Exact tests, with tied observations included guarantee the type I error rate with a better exploitation of the significance level and a larger power than the corresponding tests after the omission of tied observations. The omission of ties can produce a considerable change in the shape of the sample, and so can violate underlying test assumptions. Thus, on both theoretical and practical grounds, the recommendation to omit tied values cannot be supported, relative to analysing the whole data set in the same way whether or not ties occur, preferably with an exact permutation test.Peer reviewe

Commentary: Parasite-mediated mate preferences in a cooperatively breeding rodent

A Commentary on Parasite-mediated mate preferences in a cooperatively breeding rodent by Lutermann, H., Butler, K. B., and Bennett, N. C. (2022). Front. Ecol. Evol. 10:A838076 doi: 10.3389/fevo.2022.838076Publisher PDFPeer reviewe

Birdsbesafe® collar cover reduces bird predation by domestic cats (Felis catus)

The domestic cat (Felis catus) is one of the world’s most damaging invasive species, especially threatening to local bird populations. This study examined the efficacy of the Birdsbesafe® collar cover at reducing predation rates by household cats on avian populations. The vivid colours of the Birdsbesafe® collar cover are assumed to alert nearby birds to the cat’s presence, allowing them to escape safely. Overall, 19 cats were trialled over 8 weeks and the Birdsbesafe® collar cover resulted in a reduction of 78% in the number of birds killed. Further research is required into owner attitudes to collars in order to examine whether these collar‐based devices could be widely adopted.PostprintPeer reviewe

A review of thanatosis (death feigning) as an anti-predator behaviour

Thanatosis—also known as death-feigning and, we argue more appropriately, tonic immobility (TI)—is an under-reported but fascinating anti-predator strategy adopted by diverse prey late on in the predation sequence, and frequently following physical contact by the predator. TI is thought to inhibit further attack by predators and reduce the perceived need of the predator to subdue prey further. The behaviour is probably present in more taxa than is currently described, but even within well-studied groups the precise taxonomic distribution is unclear for a number of practical and ethical reasons. Here we synthesise the key studies investigating the form, function, evolutionary and ecological costs and benefits of TI. This review also considers the potential evolutionary influence of certain predator types in the development of the strategy in prey, and the other non-defensive contexts in which TI has been suggested to occur. We believe that there is a need for TI to be better appreciated in the scientific literature and outline potentially profitable avenues for investigation. Future use of technology in the wild should yield useful developments for this field of study.Publisher PDFPeer reviewe