Increased turning per unit distance as an area-restricted search mechanism in a pause-travel predator, juvenile plaice, foraging for buried bivalves

During searching, discovery of a prey patch by juvenile plaice Pleuronectes platessa was associated with a change from extensive to intensive search behaviour several moves before an attack on a prey. Intensive search behaviour was characterized by reduced distance of moves, a greater rate of turning per unit distance and shorter pauses between moves. The increase in turn rate was associated with area-restricted seaching, while a decrease in distances moved suggests that plaice search more efficiently for prey when stationary than while moving. The klinokinetic mechanism that appears to regulate search behaviour in juvenile plaice should allow efficient exploitation of a range of prey distribution patterns based on localized cues alone. Such a mechanism is especially useful to a migratory predator, like plaice, whose foraging is subject to time constraints imposed by tidally available feeding areas.     

The effect of habitat complexity on the functional response of a seed-eating passerine

Recent population declines of seed-eating farmland birds have been associated with reduced overwinter survival due to reductions in food supply. An important component of predicting how food shortages will affect animal populations is to measure the functional response, i.e. the relationship between food density and feeding rate, over the range of environmental conditions experienced by foraging animals. Crop stubble fields are an important foraging habitat for many species of seed-eating farmland bird. However, some important questions remain regarding farmland bird foraging behaviour in this habitat, and in particular the effect of stubble on farmland bird functional responses is unknown. We measured the functional responses of a seed-eating passerine, the Chaffinch Fringilla coelebs , consuming seeds placed on the substrate surface in three different treatments: bare soil, low density stubble and high density stubble. Stubble presence significantly reduced feeding rates, but there was no significant difference between the two stubble treatments. Stubble reduced feeding rates by reducing the maximum attack distance, i.e. the distance over which an individual food item is targeted and consumed. The searching speed, handling time per seed, proportion of time spent vigilant, duration of vigilance bouts and duration of head-down search periods were unaffected by the presence of stubble. The frequency of vigilance bouts was higher in the bare soil treatment, but this is likely to be a consequence of the increased feeding rate. We show the influence of a key habitat type on the functional response of a seed-eating passerine, and discuss the consequences of this for farmland bird conservation.     

Pollinator functional response and plant population dynamics: Pollinators as a limiting resource

Summary During recent years, much work has focused on which factors limit the reproductive success in plants. Several studies show a strong influence of either resource limitation, pollen limitation or a combined effect of both. The theoretical arguments for resource limitation are abundant, but there has been very little work done concerning the effect of pollinator availability. In this paper we construct a model to study how the reproductive success in plants is influenced by the foraging behaviour of the pollinators. The pollinator population is assumed to have a constant population density. A functional response function for the pollinators is derived. It is similar to a Holling type II functional response. It is shown that, since the pollinators are regulated by factors not included in the model and their capability to pollinate is limited by the functional response, this is sufficient for regulating the plant population. There also exists a threshold condition for the persistence of the plant population that depended on the search rate of the pollinators and the demographic parameters of the plant population. If this threshold condition is not satisfied the plant population cannot persist and will become extinct. If the condition is satisfied the plant population grows until it is limited at the equilibrium mentioned above.     

Interplay of individual interactions and turbidity affects the functional response of three-spined sticklebacks Gasterosteus aculeatus

The effects of turbidity, size and the presence of conspecifics on the functional response, feeding latency and activity in the three-spined stickleback Gasterosteus aculeatus were examined. A significant interaction between standard length and presence of conspecifics demonstrated an increase in attack rates of larger individuals in the presence of conspecifics. Attack rate was also higher in turbid water. Feeding latency decreased with prey concentration and presence of conspecifics, but was not affected by turbidity. Activity level did not change with prey levels, but increased with turbidity. These results can help to better understand how individual flexibility in the functional response can affect prey mortality according to environmental perturbation and social interaction at the level of the predator.     

Plankton‐picking by the goatfish Pseudupeneus maculatus(Mullidae), a specialized bottom forager

Although goatfishes (Mullidae) include c . 50 specialized bottom foraging species, juvenile and adult spotted goatfish Pseudupeneus maculatus were recorded feeding on plankton on rocky reefs off southern and north‐eastern Brazil, respectively.     

Effects of host on functional response of offspring in two populations of Trissolcus grandis on the sunn pest

Trissolcus grandis Thompson is the most important egg parasitoid of Eurygaster integriceps Put. in Iran. It can be reared on some alternative hosts such as eggs of Podisus maculiventris (Say). In this study, the functional response of female wasps that emerged from the factitious host, P. maculiventris, has been compared with that of females that emerged from the primary host, E. integriceps. In both wasp groups, at 23 ± 1°C, 70 ± 10% relative humidity and 15.00 : 9.00 hours (L : D) photoperiod, a type III functional response was observed. Parameters of Holling's disk equation for both populations were estimated and compared with an equation with indicator variable. Estimated handling time for females that emerged from Eurygaster and Podisus eggs are 0.62 and 0.77 h and parameter b, which describes the change in attack rate with host density in a type III functional response, was 0.004 and 0.005, respectively. The results indicated that the functional responses of the two populations differed in handling time. Longer handling time in wasps that emerged from factitious host showed that the wasps have lower quality in comparison with the wasps that emerged from primary host. This may be the first evidence of the effect of host on functional response of offspring and a promising result for use of functional response in quality testing.     

Measuring the functional responses of farmland birds: an example for a declining seed-feeding bunting

1. Many farmland bird species have undergone significant declines. It is important to predict the effect of agricultural change on these birds and their response to conservation measures. This requirement could be met by mechanistic models that predict population size from the optimal foraging behaviour and fates of individuals within populations. A key component of these models is the functional response, the relationship between food and competitor density and feeding rate. 2. This paper describes a method for measuring functional responses of farmland birds, and applies this method to a declining farmland bird, the corn bunting Miliaria calandra L. We derive five alternative models to predict the functional responses of farmland birds and parameterize these for corn bunting. We also assess the minimum sample sizes required to predict accurately the functional response. 3. We show that the functional response of corn bunting can be predicted accurately from a few behavioural parameters (searching rate, handling time, vigilance time) that are straightforward to measure in the field. These parameters can be measured more quickly than the alternative of measuring the functional response directly. 4. While corn bunting violated some of the assumptions of Holling's disk equation (model 1 in our study), it still provided the most accurate fit to the observed feeding rates while remaining the most statistically simple model tested. Our other models may be more applicable to other species, or corn bunting feeding in other locations. 5. Although further tests are required, our study shows how functional responses can be predicted, simplifying the development of mechanistic models of farmland bird populations.     

捕食性昆虫的功能反应方程及其参数的估算

昆虫的功能反应是指每头捕食者在一定时间内的捕食量对猎物密度变化的反应。该文介绍描述这种功能反应的圆盘方程 (Ⅱ型 )的由来及其参数的估测方法 ,简要讨论了影响昆虫功能反应测定的主要因素。     

Foraging mode of the chameleon,Bradypodion pumilum: a challenge to the sit‐and‐wait versus active forager paradigm?

Foraging mode is an important aspect of life history, often associated with traits such as locomotor mode, energy budget, risk of predation and reproductive effort. Because of these life-history associations, classification of foraging mode can be conceptually useful. Lizards figured prominently in the historical development of foraging mode concepts, yet our current understanding is dominated by only two lizard families which are good examples of the two extreme modes, sit-and-wait vs. active foraging. A great deal of lizard phylogenetic diversity remains unrepresented. Chameleons are a highly derived lizard taxon for which we have very little behavioural or ecological data, and no foraging mode data. Because chameleons are so unusual, it is not possible to predict where they will fit within the bimodal paradigm. I studied time budget and foraging mode in the Cape dwarf chameleon, Bradypodion pumilum , in Stellenbosch, South Africa. Several approaches were taken to assess foraging behaviour. First, lag-sequential analysis was applied to compare rates behaviours associated with observed eating events, which did not support a sit-and-wait foraging mode. Second, the number of moves per minute (MPM) and per cent time moving (%TM) were compared with those of other lizard taxa from the literature. Foraging in B. pumilum was found to be most consistent with an active foraging mode, although the MPM is unusually low. Thus I propose classification of B. pumilum as a cruise forager. Sufficient data are available to define a discriminant function for active vs. sit-and-wait modes among lizard speries, which classifys B. pumilum as active and additionally lends statistical support for good separation between foraging modes. These findings are discussed in relation to the evolution of foraging modes in chameleons and other lizard families.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 797–808.     

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 II ('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.     

Time‐series models to quantify short‐term effects of meteorological conditions on bumblebee forager activity in agricultural landscapes

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避难所对七星瓢虫捕食桃蚜功能反应的影响

自然情况下的捕食是以植物为中介发生的。作者采用植物模型作为捕食环境,测试了单纯的物理因素(避难所)对七星瓢虫Coccinella septempunctata L.捕食桃蚜Myzus persicae(Sulzer)的功能反应的影响。结果表明,避难所的存在能造成七星瓢虫捕食量和捕食率极显著下降,对雄虫的影响显著比雌虫强,且在中等猎物密度时影响更为突出。Logistic回归分析发现,七星瓢虫雌虫和雄虫无论避难所是否存在,功能反应类型均为HollingⅡ型。避难所不存在的情况下,雌、雄成虫的圆盘方程分别为N a=1.0259 N0/(1+0.003078 N0)和N a=0.9246 N0/(1+0.002127 N0),避难所存在的情况下,其圆盘方程分别为N a=0.9500 N0/(1+0.00342 N0)和N a=0.6463N0/(1+0.002262 N0)。避难所的存在能导致两性成虫瞬时攻击率极显著下降,但仅雄虫处置时间极显著延长,说明雄虫在环境异质性较高时捕获猎物更困难。     

Environmental heterogeneity amplifies behavioural response to a temporal cycle

Resource acquisition is integral to maximise fitness, however in many ecosystems this requires adaptation to resource abundance and distributions that seldom stay constant. For predators, prey availability can vary at fine spatial and temporal scales as a result of changes in the physical environment, and therefore selection should favour individuals that can adapt their foraging behaviour accordingly. The tidal cycle is a short, yet predictable, temporal cycle, which can influence prey availability at temporal scales relevant to movement decisions. Here, we ask whether black‐legged kittiwakes Rissa tridactyla can adjust their foraging habitat selection according to the tidal cycle using GPS tracking studies at three sites of differing environmental heterogeneity. We used a hidden Markov model to classify kittiwake behaviour, and analysed habitat selection during foraging. As expected for a central‐place forager, we found that kittiwakes preferred to forage nearer to the breeding colony. However, we also show that habitat selection changed over the 12.4‐h tidal cycle, most likely because of changes in resource availability. Furthermore, we observed that environmental heterogeneity was associated with amplified changes in kittiwake habitat selection over the tidal cycle, potentially because environmental heterogeneity drives greater resource variation. Both predictable cycles and environmental heterogeneity are ubiquitous. Our results therefore suggest that, together, predictable cycles and environmental heterogeneity may shape predator behaviour across ecosystems.     

Prey selection and efficiency of naïve and experienced juvenile sockeye salmon

Prey selection and growth efficiency of juvenile sockeye salmon Oncorhynchus nerka switched between live prey and pelleted diets were investigated. First feeding sockeye salmon fry were placed into one of three dietary treatments for 7 months prior to assessing potential differences with a growth and a behavioural assay. Dietary treatments were (1) adult Artemia franciscana for 1 month, followed by pelleted feed for an additional 6 months ( Art − BD), (2) pelleted feed from first feeding for 7 months (BD) and (3) adult A. franciscana for 1 month, and a combination of pelleted feed and live adult A. franciscana for 6 months ( Art + BD). Equal numbers from each treatment group were then tagged, pooled into replicate 'common garden' tanks and fed novel live prey items ( Daphnia sp. and mosquito Culex pipiens larvae) for an additional 3 weeks. No significant differences in the growth efficiency of sockeye salmon were found during the 3 week feeding trial on the novel prey items. Additional sockeye salmon from each dietary treatment were used in a behavioural assay to determine if the treatments had an impact on foraging efficiency (prey selection or time to capture prey). No significant differences in prey selection were found among treatment groups in time to capture pellets, A. franciscana or mosquito larvae. Also, no significant differences were found within treatment groups in time to capture different food sources. No substantive benefits in foraging efficiency of sockeye salmon associated with prior exposure to live prey were demonstrated. This suggests that altering existing hatchery practices for juvenile sockeye salmon by offering live food prior to release is unlikely to influence post-hatchery feeding behaviour or increase post-release survival.     

Satiation and the functional response: a test of a new model

Abstract. 1. A model of the functional response to prey density is derived to include the reduction in time available for search, T_s , resulting from predator satiation.
2. For larger prey items predator satiation occurs at each prey capture and T_s is reduced by the attack time and digestive pause of a series of attack cycles. For small prey items predator foraging is continuous at low densities with T_s reduced solely by attack time. At higher densities predator satiation occurs after the capture of several small prey items and T_s is reduced by the attack time and digestive pause of a series of foraging cycles.
3. A comparison of the predicted asymptotic level of prey capture using experimentally estimated parameter values, with the maximum consumption of aphids by larval and adult coccinellids provides a test of the satiation model.
4. The limitation of prey capture by predator satiation is discussed with reference to handling time and the success of coccinellids in biological control.