Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type 11 ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching. A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (< 150/m(-2)). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote. A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81 % of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3 %), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93 % of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.

Spatial overlap of grey seals and fisheries in Irish waters, some new insights using telemetry technology and VMS

Seals and humans often target the same food resource, leading to competition. This is of mounting concern with fish stocks in global decline. Grey seals were tracked from southeast Ireland, an area of mixed demersal and pelagic fisheries, and overlap with fisheries on the Celtic Shelf and Irish Sea was assessed. Overall, there was low overlap between the tagged seals and fisheries. However, when we separate active (e.g. trawls) and passive gear (e.g. nets, lines) fisheries, a different picture emerged. Overlap with active fisheries was no different from that expected under a random distribution, but overlap with passive fisheries was significantly higher. This suggests that grey seals may be targeting the same areas as passive fisheries and/or specifically targeting passive gear. There was variation in foraging areas between individual seals suggesting habitat partitioning to reduce intra-specific competition or potential individual specialisation in foraging behaviour. Our findings support other recent assertions that seal/fisheries interactions in Irish waters are an issue in inshore passive fisheries, most likely at the operational and individual level. This suggests that seal population management measures would be unjustifiable, and mitigation is best focused on minimizing interactions at nets.

The role of dietary breadth in national bumblebee (Bombus) declines: Simple correlation?

Bumblebee species declines have been reported in Europe, North America and Asia. Loss of suitable habitat to agricultural intensification is considered to be the main cause of declines in Europe. Differential impacts on species have been recorded but insufficient knowledge of species ecology means that effective conservation management prescriptions cannot be put into place with certainty. Dietary specialisation, specifically on flowers of Fabaceae, has been hypothesised as driving differential declines but the reliability of previous studies has been questioned. Here we present a three-year study of the foraging behaviour of two UK Biodiversity Action Plan bumblebee species. For the first time, analysis of nectar and pollen foraging was performed on sites where nationally rare UK bumblebees were as abundant as more nationally ubiquitous species. Results indicated that the nationally rare Bombus sylvarum collected the majority of its pollen from flowers of Odontites verna and had a significantly narrower mean nectar dietary breadth than ecologically similar species Bombus humilis and Bombus pascuorum (p = 0.004 and 0.008 respectively). In contrast, the dietary breadth of the nationally rare B. humilis was similar to the more nationally ubiquitous species B. pascuorum and Bombus lapidarius. Moreover, B. lapidarius was recorded as having the narrowest pollen dietary breadth, collected pollen from the least number of floral taxa and was the most specialised of the Bombus species on pollen of Fabaceae. Patterns of dietary specialization were inconsistent with national declines and results highlighted a need for further detailed investigation into the factors contributing to differential declines.

Distribution and at-sea activity of a nocturnal seabird, the Bulwer's petrel Bulweria bulwerii, during the incubation period

Bulwer'spetrelsarenocturnalseabirdsthatmostlypreyonmesopelagicfauna.Asaerialforagersand shallowdivers,theirfeedingopportunitiesarelimitedbynear-surfaceavailabilityoftheirprey,whichis highlyvariablebothtemporally(reflectingdiurnalandlunarcycles)andspatially.Herewestudiedhow Bulwer'spetrelscopewiththeseconstraintsbyanalysingtheirat-seadistributionandactivityduringthe incubationperiod.Wetrackedthemovementsof20birdsfromSelvagemGrande(NEAtlantic)duringa completelunarcycle,andrecorded30foragingtripsthatlasted11daysonaverage.Birdswereboth distributedaroundthecolonyandinwatersclosetotheAzoreanarchipelago(mid-Atlantic)located 1700kmaway,andweresignificantlymoreactiveatnight(especiallyjustaftersunsetandbeforesunrise), whenmesopelagicfaunaisalsoclosertotheseasurfaceduetotheirdielverticalmigrations.Bulwer's petrelsspentsignificantlymoretime flyingduringmoonlight,althoughtheeffectofthemoonwasrela- tivelyweak(ca.10–15%differencebetweenmoonlitanddarkperiodsofthenight),andnotobviouswhen birdswereforaginginmid-Atlanticwaters,whichwerealsotargetedmoreoftenduringfull-moon.These resultsrevealkeyadaptationsoftheBulwer'spetreltothehighlydynamicecologyofitsmesopelagicprey.

Feeding habits of the velvet belly lanternshark Etmopterus spinax (Chondrichthyes : Etmopteridae) off the Algarve, southern Portugal

Etmopterus spinax is one of the most abundant predators of the upper continental slope off the Algarve (southern Portugal), where it is captured in large quantities in deep-water fisheries. The feeding habits of E. spinax off the Algarve were investigated through the analysis of stomach contents of 376 individuals. Prey composition was described and maturity, sex and size related variations in the diet analysed. The overall diet of E. spinax suggested a fairly generalized benthopelagic foraging behaviour primarily tuned to pelagic macroplankton/microneckton, teleost fish and cephalopods. Sex and maturity related differences in the diet were not significant. Two main ontogenic diet shifts were observed at about 17 and 28 cm total length. Small and medium sized immature sharks had a diet dominated by eurybathic crustaceans, chiefly Meganyctiphanes norvegica and Pasiphaea sivado. Larger individuals consumed more teleosts and cephalopods, in part associated with scavenging as a new feeding strategy. With increasing shark size the diet diversified both in terms of resources exploited and prey size.

Avian trait-mediated vulnerability to road traffic collisions

Collision with vehicles is an important source of bird mortality, but it is uncertain why some species are killed more often than others. Focusing on passerines,we testedwhether mortality is associated with bird abundances, and with traits reflecting flight manoeuvrability, habitat, diet, and foraging and social behaviours. We also tested whether the species most vulnerable to road-killing were scarcer near (b500 m) or far (N500–5000 m) from roads. During the breeding seasons of 2009–2011,we surveyed roadkills daily along 50 km of roads, and estimated bird abundances from 74 point counts. After correcting for phylogenetic relatedness, there was strong correlation between roadkill numbers and the abundances of 28 species counted near roads. However, selectivity indices indicated that Blue tit (Parus caeruleus), Blackcap (Sylvia atricapilla) and European goldfinch (Carduelis carduelis) were significantly more road-killed than expected from their abundances, while the inverse was found for seven species. Using phylogenetic generalised estimating equations, we found that selectivity indexes were strongly related to foraging behaviour and habitat type, and weakly so to body size, wing load, diet and social behaviour. The most vulnerable passerines were foliage/bark and swoop foragers, inhabiting woodlands, with small body size and low wing load. The species most vulnerable to road collisions were not scarcer close to roads. Overall, our study suggests that traits provide a basis to identify the passerine species most vulnerable to road collisions, which may be priority targets for future research on the population-level effects of roadkills.

Unlocking ecological history using fish remains: Eco-evolutionary consequences of exploitation in the Atlantic bluefin tuna

During recent decades, the health of ocean ecosystems and fish populations has been threatened by overexploitation, pollution, and anthropogenic-driven climate change. Due to a lack of long-term data, we have a poor understanding of when intensive exploitation began and what impact anthropogenic activities have had on the ecology and evolution of fishes. Such information is crucial to recover degraded and depleted marine ecosystems and fish populations, maximise their productivity in-line with historical levels, and predict their future dynamics. In this thesis, I evaluate anthropogenic impacts on the iconic Atlantic bluefin tuna (Thunnus thynnus; BFT), one of the longest and recently most intensely exploited marine fishes, with a tremendous cultural and economic importance. Using a long-time series of archaeological and archived faunal remains (bones) dating back to approximately two millennia ago, I apply morphological, isotopic, and genomic techniques to perform the first studies on long-term BFT size and growth, diet and habitat use, and demography and adaptation, and produce the first genome-wide data on this species. My findings suggest that exploitation had impacted BFT foraging behaviour by the ~16th century when coastal ecosystem degradation induced a pelagic shift in diet and habitat use. I reveal that BFT biomass began to decline much earlier than hitherto documented, by the 19th century, consistent with intensive tuna trap catches during this period and catch-at-size increasing. I find that BFT juvenile growth had increased by the early 1900s (and more dramatically by the 21st century) which may reflect an evolutionary response to size selective harvest–which I find putative genomic signatures of. Further, I observed that BFT foraging behaviours have been modified following overexploitation during the 20th century, which previously included a isotopically distinct, Black Sea niche. Finally, I show that despite biomass declining from centuries ago, BFT has retained genomic diversity.

Foraging and vein-cutting behaviour of Euploea core corinna (W.S. Macleay) (Lepidoptera : Nymphalidae) caterpillars feeding on latex-bearing leaves

Caterpillars of Euploea core corinna (W. S. Macleay) sever leaf veins prior to feeding on their latex-bearing host plants, which restricts the flow of latex at feeding sites. The severing of leaf veins by insects feeding on latex-bearing plants is commonly referred to as 'sabotaging' and is thought to be an evolved response by the insect to counter the negative effects of feeding on latex-rich leaves. Sabotaging behaviour is described for all instars of E. core corinna, with particular attention given to neonates. Vein cutting by neonate E. core corinna caterpillars can occur within 2 h of hatching, with most caterpillars establishing feeding sites within 10 h. Commonly, first instars cut an are-shaped row of leaf side-veins parallel to the leaf margin, but they may also cut the leaf mid-rib in a fashion similar to older instar larvae. From a sample of 50 E. core corinna larvae, representing all instars, we found that the diameters of the veins cut by caterpillars are closely correlated to larval head width (r=0.90). Through manipulative experiments, we demonstrate for the first time that sabotaging behaviour in neonate caterpillars imposes no detectable short-term physiological costs on those caterpillars.

Habitat choice and vigilance behaviour of brush-tailed rock-wallabies (Petrogale penicillata) within their nocturnal foraging ranges

Habitat choice by brush-tailed rock-wallabies (Petrogale penicillata) in south-east Queensland was investigated by comparing the attributes of the nocturnal foraging locations that they selected with those of random locations within a radius of 50 m. Brush-tailed rock-wallabies were shown to select foraging locations on the basis of forage quality and/or their ability to see predators, rather than protection from predators amongst vegetation that could conceal them. Habitat choice may have been affected by limited food availability, as this study was conducted in the winter dry season. The attributes of foraging locations that brush- tailed rock-wallabies perceived as increasing their predation risk were assessed by recording the proportion of time that brush- tailed rock-wallabies spent vigilant while foraging. To measure vigilance, focal animals were observed with a night- vision scope for two minutes and the proportions of time spent vigilant and feeding were recorded. No measured feature of foraging locations was related to higher vigilance levels, suggesting that brush- tailed rock-wallabies did not alter their vigilance whether sheltered amongst grass tussocks or in open habitat, or whether feeding on good quality or poorer quality vegetation. Vigilance levels significantly declined as overnight temperatures decreased, which may have resulted from higher energy requirements of brush- tailed rock-wallabies during winter. The only factors that were found to significantly increase vigilance levels were high winds and moonlit nights. On bright nights, brush- tailed rock-wallabies were very unsettled and during high winds they often did not emerge to feed. More information is needed about how macropods detect predators at night before the effects of wind and light intensity upon vigilance can be fully understood.

Food profitability affects intranidal recruitment behaviour in the stingless bee Nannotrigona testaceicornis

Does the food's sugar concentration affect recruitment behaviour in the stingless bee Nan-notrigona testaceicornis? We recorded intranidal forager behaviour while offering sugar water of constant, increasing, or decreasing concentrations. Running speed was not correlated with sugar concentration but the jostling contacts/sec were. Food profitability also affected the recruiter's thorax vibrations: Pulse duration and duty cycle followed both concentration increases and decreases. Sugar concentration also influenced the number of recruited bees. In comparison to the phylogenetically closely related Scaptotrigona, Nan-notrigona's intranidal recruitment behaviour showed a more elaborate association with food profitability. This is likely to reflect differences in ecology and foraging strategies as Nannotrigona - in contrast to Scaptotrigona - does not lay scent trails to guide recruits to a food source.

Optimal patch-leaving behaviour: a case study using the parasitoid Cotesia rubecular

1. Parasitoids are predicted to spend longer in patches with more hosts, but previous work on Cotesia rubecula (Marshall) has not upheld this prediction, Tests of theoretical predictions may be affected by the definition of patch leaving behaviour, which is often ambiguous. 2. In this study whole plants were considered as patches and assumed that wasps move within patches by means of walking or flying. Within-patch and between-patch flights were distinguished based on flight distance. The quality of this classification was tested statistically by examination of log-survivor curves of flight times. 3. Wasps remained longer in patches with higher host densities, which is consistent with predictions of the marginal value theorem (Charnov 1976). tinder the assumption that each flight indicates a patch departure, there is no relationship between host density and leaving tendency. 4. Oviposition influences the patch leaving behaviour of wasps in a count down fashion (Driessen et al. 1995), as predicted by an optimal foraging model (Tenhumberg, Keller & Possingham 2001). 5. Wasps spend significantly longer in the first patch encountered following release, resulting in an increased rate of superparasitism.

Expression of foraging and Gp-9 are associated with social organization in the fire ant Solenopsis invicta.

The aim of this study was to investigate levels of expression of two major genes, the odorant binding protein Gp-9 (general protein-9) and foraging, that have been shown to be associated with behavioural polymorphisms in ants. We analysed workers and young nonreproductive queens collected from nests of the monogyne (single reproductive queen per nest) and polygyne (multiple reproductive queens) social forms of Solenopsis invicta. In workers but not young queens, the level of foraging expression was significantly associated with social form and the task performed (ie localization in the nest or foraging area). The level of expression of Gp-9 was also associated with social form and worker localization. In addition there was a higher level of expression of the Gp-9(b) allele compared with the Gp-9(B) allele in the heterozygote workers and the young nonreproductive queens. Finally, in the polygyne colonies the level of expression of foraging was not significantly associated with the Gp-9 genotype for either workers or young nonreproductive queens, suggesting that both genes have independent non-epistatic effects on behaviour in S. invicta.

Social structure emerges via the interaction between local ecology and individual behaviour.

1. The formation of groups is a fundamental aspect of social organization, but there are still many questions regarding how social structure emerges from individuals making non-random associations. 2. Although food distribution and individual phenotypic traits are known to separately influence social organization, this is the first study, to our knowledge, experimentally linking them to demonstrate the importance of their interaction in the emergence of social structure. 3. Using an experimental design in which food distribution was either clumped or dispersed, in combination with individuals that varied in exploratory behaviour, our results show that social structure can be induced in the otherwise non-social European shore crab (Carcinus maenas). 4. Regardless of food distribution, individuals with relatively high exploratory behaviour played an important role in connecting otherwise poorly connected individuals. In comparison, low exploratory individuals aggregated into cohesive, stable subgroups (moving together even when not foraging), but only in tanks where resources were clumped. No such non-foraging subgroups formed in environments where food was evenly dispersed. 5. Body size did not accurately explain an individual's role within the network for either type of food distribution. 6. Because of their synchronized movements and potential to gain social information, groups of low exploratory crabs were more effective than singletons at finding food. 7. Because social structure affects selection, and social structure is shown to be sensitive to the interaction between ecological and behavioural differences among individuals, local selective pressures are likely to reflect this interaction.