Prey Shortage Research Articles

Increased bat hunting at polluted streams suggests chemical exposure rather than prey shortage

Streams and their riparian areas are important habitats and foraging sites for bats feeding on emergent aquatic insects. Chemical pollutants entering freshwater streams from agricultural and wastewater sources have been shown to alter aquatic insect emergence, yet little is known about how this impacts insectivorous bats in riparian areas. In this study, we investigate the relationships between the presence of wastewater effluent, in-stream pesticide toxicity, the number of emergent and flying aquatic insects, and the activity and hunting behaviour of bats at 14 streams in southwestern Germany. Stream sites were located in riparian forests, sheltered from direct exposure to pollutants from agricultural and urban areas. We focused on three bat species associated with riparian areas: Myotis daubentonii, M. cf. brandtii, and Pipistrellus pipistrellus. We found that streams with higher pesticide toxicity and more frequent detection of wastewater also tended to be warmer and have higher nutrient and lower oxygen concentrations. We did not observe a reduction of insect emergence, bat activity or hunting rates in association with pesticide toxicity and wastewater detections. Instead, the activity and hunting rates of Myotis spp. were higher at more polluted sites. The observed increase in bat hunting at more polluted streams suggests that instead of reduced prey availability, chemical pollution at the levels measured in the present study could expose bats to pollutants transported from the stream by emergent aquatic insects.

Brood reduction caused by sibling cannibalism in Isodontia harmandi (Hymenoptera: Sphecidae), a solitary wasp species building communal brood cells.

Sibling rivalry or brood reduction prevailing within bird nests is effectively avoided in solitary aculeate nests because the larvae of wasps and bees usually develop in each brood cell. However, a solitary wasp species, Isodontia harmandi, allows us to study brood reduction in a communal brood cell, where up to a dozen larvae develop in a group relying on prey provisioned by a female wasp. To demonstrate brood reduction in this species, we collected nests at various developmental brood stages from fields for five years (2010–2015). There was a significant decrease in the brood size between the nests sampled at the egg or hatchling stages and those at later stages when analyzing only data excluding nests that were parasitized, attacked by predators, or containing deteriorated prey. In whole brood-rearing experiments, we also confirmed that brood reduction occurred in 30 of 39 nests during larval stages and in 23 nests after cocoon stage. Larval survival was affected positively by total prey weight and negatively by brood size, though cocoon survival was not affected. A third-quarter (76%) of larval death was identified as sibling cannibalism through observation by time-lapse recording on multi-larvae rearing experiments. Therefore, we conclude that brood reduction routinely occurs as a result of sibling cannibalism in I. harmandi. Additionally, as we could not detect any positive effects of clutch size on the amount of provision, female wasps might overproduce offspring due to the unpredictability of available prey resources. Differences in brood size and reduction among sex categories were undetected, except for parental provisions. Thus, sibling cannibalism may efficiently regulate brood size in communal brood cells under prey shortage.

Differential responses of coexisting owls to annual small mammal population fluctuations in temperate mixed forest

Montane temperate forests in central and southern Europe host diverse small mammal assemblages, but the fluctuations in these assemblages in correlation with owl predators are still poorly explored. The key questions of our study were how coexisting owls responded to different prey fluctuations and whether any particular small mammal species governed predator–prey co‐dynamics. We conducted a long‐term study (2004–2020) in low‐elevation (300–1100 m above sea level) mixed Beech and Silver Fir forest in the northern Dinaric Alps (central Slovenia). Monitoring data on the main small mammal groups – mice Muridae, voles Cricetidae, dormice Gliridae and shrews Soricidae – and three owl species – the Ural Owl Strix uralensis, Tawny Owl Strix aluco and Boreal Owl Aegolius funereus – were collected annually. To find relationships between prey and predator populations, we used two types of supervised machine learning approaches and addressed three predictive modelling tasks of multi‐target regression. The dominant species in the small mammal assemblage, the Yellow‐necked Mouse Apodemus flavicollis, had a key role in determining predator populations and their breeding performance. We noted higher sensitivity to small mammal fluctuations in boreal zone owl species (Boreal Owl and Ural Owl), which reach their southern distribution limit in the Dinaric Alps, whereas the temperate zone species (Tawny Owl) seemed to be less affected. In years of prey shortage, the Boreal Owl was found to presumably abandon its territories, the Ural Owl suppressed breeding and the Tawny Owl sustained breeding activity by shifting prey selection. Low‐elevation forests appeared to be suboptimal habitat for the competitive subordinate Boreal Owl, which may exploit occasional outbreaks of small mammal populations in these habitats even in the presence of larger competitors. Whether low‐elevation forests can play a role in maintaining threatened and cold‐adapted Boreal Owl populations in central and southern Europe in the face of recent ecosystem changes due to climate and environmental changes remains an open scientific question.

Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer

The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4–6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success.

Fishery discards do not compensate natural prey shortage in Northern gannets from the English Channel

Fisheries modify ecosystem balance by harvesting through marine food webs and producing large amounts of discards subsidizing scavengers. Among them, seabirds are the most conspicuous and have been benefiting from anthropogenic food sources generated by fisheries. However, this modified feeding behaviour also exposes them to threats, such as accidental bycatch on fishing gear and ecological traps set by discards of lower nutritional value compared to seabird natural prey. Seabird-fishery interactions have been the focus of numerous studies, but very few integrative investigations tested multi-annual dynamics. To explore this temporal dimension, we performed stable isotopic and body condition analyses, as well as GPS-tracking in Northern gannets (Morus bassanus) over a 12-year period (2005–2017), during which they coexisted with fisheries in the English Channel. We demonstrate that gannets fed either on natural prey, or fishery wastes, but that discard consumption induced increased seabird foraging effort and reduced adult body condition. These changes are concomitant with reduced gannet reproductive success, and reduced growth rate of their breeding population. Our work provides essential, novel understanding of scavengers-fisheries interactions, by showing that fishery discards do not compensate natural prey shortage in the longer term. Altered gannet foraging and fitness strongly suggest pelagic fish depletion threatening Northern gannets in the English Channel. To improve gannet conservation in this ecoregion, fishery discards may be banned, but, efforts should in priority go towards rebuilding Northern gannet pelagic prey populations, particularly by strongly reducing fishing effort on North Atlantic mackerel.

A Systematic Review on the Effects of Plant-Feeding by Omnivorous Arthropods: Time to Catch-Up With the Mirid-Tomato Bias?

Zoophytophagous (omnivorous) predators provide valuable pest control services, and offer an advantage over strict carnivores as plant-feeding enables survival during prey shortage. This putative advantage can potentially be their downside, as plant-feeding may entail damage that negatively affects plant growth/yield (i.e., the cost arising from of omnivore plant-feeding). Yet, benefits conferred by predatory services are usually thought to counterbalance any impact of plant damage. In this systematic review, our goal was to determine how often levels of omnivore damage and its consequences for plants (costs) are considered or quantified. We provide a synthesis of publication trends and findings on omnivore plant-feeding levels, plant injury variables, actual (if quantified) and potential effects on growth/yield, the type of study (lab, greenhouse) and the plants/omnivores most often examined. Our search revealed that measures of omnivore plant-feeding are occasionally reported, but seldom are the direct consequences of such damage also considered. Omnivore plant-feeding were reported in 57% of studies (53 of 93 full-text examined); within these, the majority (>80%) indicated moderate to high levels of plant-feeding. However, only 22% of reports (15 of 69) quantified the effects of omnivore-inflicted damage on plant performance. Of these 15 reports, a greater number found negative consequences for plants compared to those showing no effect (8 vs. 4; 3 with both), with consequences for yield relative to growth being more often evaluated (6 vs. 2). Overall, fruit/leaf injuries relative to stem/flower-feeding were most often examined, and lab/greenhouse experiments predominated. Tomatoes (Solanum lycopersicum) and the mirid Nesidiocoris tenuis were the most common species studied (34 and 14 reports, respectively). Our results indicate that costs to plants of omnivore-inflicted damage are often neglected. We argue that predatory benefits need to be simultaneously considered with plant-feeding effects to appropriately evaluate pest control services. Publication trends suggest that more studies are evaluating costs to plants, but a paradigm shift is still needed. Furthermore, we found that our understanding of plant-feeding and its effects is disproportionally based on studies examining tomato plants and its omnivorous biocontrol agents. To confirm the generality of findings thus far, other plant omnivore systems should be further considered.

English

Panthera pardus is a widespread mammalian carnivore, with a very broad diet range. Therefore, it is often seen as needing less protection as compared with some other predator species. However, with a 37% reduction in historic range and some subspecies critically endangered, the leopard is a species that does indeed require certain conservation attention. In Southern Africa, there are several threats facing the leopard: habitat loss, poaching, as well as killings associated with leopard-human conflict (the latter being aggravated by poorly-stocked reserves where the animals reside). In setting aside formal protected areas for the leopard and its prey, it is important to plan and stock these reserves in such a manner so as to limit potential conflict with owners of surrounding farmlands or tribal land. Focusing on the average daily energetic consumption and expenditure of the leopard in Southern Africa, this paper seeks to determine how regular successful hunts can help maintain the animal. It was found from the study that there is a very close balance between the energy consumption and expenditure of the leopard. Depopulation of a varying intensity may result from a hunting success probability below 0.5. Leopards are unlikely to persist where hunting success is reduced to 0.1 due to prey shortage. This finding is believed to provide some preliminary guidance for leopard prey stocking rates in the future.    Key words: African leopard, energy expenditure, prey stocking rate, leopard-farmer conflict, conservation, predator-prey interaction.

Behavioural and physiological responses to prey-related cues reflect higher competitiveness of invasive vs. native ladybirds

Understanding the traits that might be linked with biological invasions represents a great challenge for preventing non-target effects on local biodiversity. In predatory insects, the ability to exploit habitats for oviposition and the physiological response to prey availability differs between species. Those species that respond more readily to environmental changes may confer to their offspring a competitive advantage over other species. Here, we tested the hypothesis that the invasive Harmonia axyridis (Coleoptera: Coccinellidae) makes better use of information from a plant-prey (Vicia faba - Aphis fabae) system compared to the native Oenopia conglobata. Y-tube olfactometer bioassays revealed that both species used olfactory cues from the system, but H. axyridis exhibited a more complete response. This species was also attracted by plants previously infested by aphids, indicating the capacity to exploit volatile synomones induced in plants by aphid attack. Oocyte resorption was investigated when different olfactory stimuli were provided under prey shortage and the readiness of new oogenesis was measured when prey was available again. H. axyridis exhibited higher plasticity in oogenesis related to the presence/absence of plant-aphid volatiles. Our results support the hypothesis that H. axyridis is more reactive than O. conglobata to olfactory cues from the plant-prey system.

Artificial diet development and its effect on the reproductive performances of Propylea japonica and Harmonia axyridis

The use of augmentative biological controls in greenhouse pest management has increased the demand for predators. To meet demands, suitable artificial diets must be developed to enable fast and cost-effective mass rearing of predators. In this study, three artificial diets were developed and their suitability for immature development and survival of Japanese ladybird Propylea japonica (Thunberg) and Multi-colored Asian ladybird Harmonia axyridis (Pallas) were investigated. An artificial diet composed of shrimp, beef, beef liver, and egg yolk in a 5:4:8:4 ratio is an adequate source of nutrition for the development of immature P. japonica and H. axyridis, resulting in 83% and 68% adult emergence rates, respectively. The reproductive performances of emerging P. japonica and H. axyridis females fed the artificial diet or pea aphids were compared. The pre-oviposition period was shorter in emerging females from immature ladybirds fed an artificial diet compared with those emerging from immature ladybirds fed pea aphids. However, the total fecundity did not vary significantly. When adults were fed artificial diets, females did not lay eggs, but oviposition could be restored by feeding adults on pea aphids. The developed artificial diet can be used for the mass rearing of P. japonica and H. axyridis for biological control applications and rearing of adults during prey shortage.

Seabirds maintain offspring provisioning rate despite fluctuations in prey abundance: a multi‐species functional response for guillemots in the North Sea

Summary Seabirds that consume more than one prey type may adjust their foraging to maintain provisioning rates for their chicks. How energetically effective are these strategies, and what are the implications for the management of seabirds and their marine habitat? A multi‐species functional response links consumption rates to the availability of multiple prey types, but fitting multi‐species functional responses to field data can be difficult, requiring consumption measurements over a range of different prey abundances. Such detailed data may be especially difficult to obtain in marine ecosystems. We used annual time‐series data on chick provisioning for the common guillemot Uria aalge together with abundance indices for its two main prey (lesser sandeel Ammodytes marinus and sprat Sprattus sprattus) to parameterize a multi‐species functional response for parents provisioning chicks at a major North Sea colony from 1992 to 2005. The fitted model reproduced changes in diet and consumption rate which were consistent with changes in local prey abundance including a long‐term decline in sandeels. The model predicted that energy intake by chicks would be more sensitive to changes in sprat abundance than sandeel abundance. Guillemots appeared able to adjust their foraging tactics over a wide range of prey abundances to maintain a consistent energetic intake rate for chicks. Synthesis and applications. Our results suggest guillemot chicks obtain adequate calorific intake from their parents despite fluctuating prey abundances, conferring some resilience in the face of environmental variation. The parameterized multi‐species functional response model can be used to estimate levels of severe prey shortage that compromise provisioning. It also enables us to interpret predator consumption rates so that these can be used as a metric of prey availability. Further, quantifying trophic links between marine prey and apex predators is needed to support the development of multi‐species models in which the predators can be included. Such models are needed as tools to effectively manage the marine ecosystem, taking into account the objectives of fishing, conservation and the need to maintain Good Environmental Status.

The importance of marine vs. human-induced subsidies in the maintenance of an expanding mesocarnivore in the arctic tundra

1. Most studies addressing the causes of the recent increases and expansions of mesopredators in many ecosystems have focused on the top-down, releasing effect of extinctions of large apex predators. However, in the case of the northward expansion of the red fox into the arctic tundra, a bottom-up effect of increased resource availability has been proposed, an effect that can counteract prey shortage in the low phase of the multi-annual rodent cycle. Resource subsidies both with marine and with terrestrial origins could potentially be involved. 2. During different phases of a multi-annual rodent cycle, we investigated the seasonal dynamics and spatial pattern of resource use by red foxes across a coast to inland low arctic tundra gradient, Varanger Peninsula, Norway. We employed two complementary methods of diet analyses: stomach contents and stable isotope analysis. 3. We found that inland red foxes primarily subsisted on reindeer carrions during the low phase of a small rodent population cycle. Lemmings became the most important food item towards the peak phase of the rodent cycle, despite being less abundant than sympatric voles. Isotopic signatures of tissue from both predator and prey also revealed that red foxes near the coast used marine-derived subsidies in the winter, but these allochthonous resources did not spillover to adult foxes living beyond 20-25 km from the coast. 4. Although more needs to be learned about the link between increasing primary productivity due to climatic warming and trophic dynamics in tundra ecosystems, we suggest that changes in reindeer management through a bottom-up effect, at least regionally, may have paved the way towards the establishment of a new mesopredator in the tundra biome.

The Reproductive Tract of the Males of the Zoophytophagous Predator <i>Brontocoris tabidus</i> (Signoret) (Heteroptera: Pentatomidae) with Different Diets and Ages

Abstract: Problem statement: Brontocoris tabidus (Signoret) (Heteroptera: Pentatomidae) is a common and important species for the biological control of defoliating Lepidoptera caterpillars. Although it has a predatory feeding habit, this species make use of plant resources, which are essential for the maintenance of its population in laboratory colonies as well as in the field during periods of prey shortage. Thus B. tabidus has been considered an obligate zoophytophagous insect. However the impact of the age and herbivory on the morphology of the reproductive organs has been poorly studied in predatory Pentatomidae. The morphology of the reproductive tract of B. tabidus males with different ages and fed on different diets were analyzed. Approach: Nymphs of B. tabidus were maintained in the field with or without plants and fed on T. molitor pupae without plant (T1); T. molitor pupae and Eucalyptus cloeziana plants (T2); T. molitor pupae and Eucalyptus urophylla plants (T3) or T. molitor pupae and guava plants (Psidium guajava L.) (T4). Adults of B. tabidus obtained from each treatment were sexed in the first day of their emergence and thirty-six pairs were formed per treatment. Ten males of B. tabidus 15 and 21 days old, obtained in each treatment were dissected and the reproductive tract submitted to histological analyses. The total area of the testes of B. tabidus was measured and the data were submitted to the variance analysis and means between treatments were compared by the test of Newman-Keuls (p = 0.05). Results: The inner genitalia of B. tabidus males had red color and the testes with six follicles. Males 15 days old presented larger testes when fed on E. cloeziana (0.94 mm2), E. urophylla (0.98 mm2) or only T. molitor pupae (0.99 mm2) than with guava plants (0.76 mm2). Twenty-one days old B. tabidus males presented testes with similar size, independent of the diet. The testes follicles of B. tabidus had larger amount of spermatozoa with all diets and ages showing that the spermatogenesis process was completed. The testes of this predator showed similar histological characteristics with all diets. Conclusion: The herbivory change the morphology of the reproductive tract of B. tabidus males in field conditions resulting in testes with different sizes, but it does not affect the histology of the reproductive organ of this predator. Therefore, the food type supplied to B. tabidus males does not affect the spermatogenesis process in this natural enemy.

Survival and Reproduction of Podisus nigrispinus (Heteroptera: Pentatomidae): Effects of Prey Scarcity and Plant Feeding

The spined soldier bug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) is a generalist predator that can alternatively feed on plant tissue to survive under prey scarcity. This research aimed to evaluate the effects of plant feeding forced by a shortage of prey on the survival and reproduction of P. nigrispinus on Eucalyptus urophylla S.T. Blake�(Myrtaceae)�plantsinthefield.� Podisus nigrispinus adults were enclosed on branches of eucalyptus by using gauze bags. These adults were fed daily with Tenebrio molitor pupae (T1) or after 5 (T2), 10 (T3) or 15 (T4) days from mating to simulate prey shortage. The pre-oviposition period, number of egg masses, number and viability of eggs and longevity of females were evaluated. Females of P. nigrispinus had a longer pre-oviposition period and produced lower number of egg masses as the period of prey shortage increased. However, the average number of eggs per egg mass, emergence of nymphs and longevity of P. nigrispinus females were not affected by prey shortage. Females of P. nigrispinuscansurvive�15�dayswithoutpreybyfeedingoneucalyptusleavesandifitfindsprey� afterwards can still reproduce. This shows that plant feeding is a successful incidental strategy to survive periods of foodscarcity�(andthusincreasetheefficiency)�ofthispredatorasabiologicalcontrolagent.

Risk of damage to tomato crops by the generalist zoophytophagous predatorNesidiocoris tenuis(Reuter) (Hemiptera: Miridae)

Nesidiocoris tenuis (Reuter) (Hem. Miridae) is a native zoophytophagous predator of the Mediterranean region, and its populations colonize tomato crops when they are not heavily treated with insecticides. This generalist predator has a high capacity for controlling insect pests, and it is currently commercially produced and released in some areas to control Bemisia tabaci (Gennadius) (Hem. Aleyrodidae). However, its status as a pest and/or as beneficial is controversial. Therefore, the aim of this study was to evaluate the risk of damage to tomatoes in extreme conditions of prey scarcity, as well as high predator populations. Three predator densities were tested in a greenhouse cage experiment during a summer tomato crop. The crop did not display any negative effect caused by the predators during the first six weeks of interaction, independently of the density released. However, subsequently, the effect was dramatic, both on the vegetative growth of the plant and on the production of fruits. The reduction in vegetative growth was located at truss eight and it was expressed mainly by a lower number of leaves and a shorter length of the shoot above the truss. There was a significant reduction of yield with a lower number of fruits collected and a smaller mean weight, although this was not observable until truss seven. It seems that feeding on the plant by this mirid bug competed with the vegetative growth and fruiting processes of the plant in the extreme conditions of prey shortage maintained in our experiment.

The effect of sand depth, feeding regime, density, and body mass on the foraging behaviour of a pit‐building antlion

Abstract 1. Pit‐building antlions are small sit‐and‐wait arthropod predators, which dig conical pits in sandy soils. We studied how biotic (conspecific density and feeding regime) and abiotic (sand depth) factors affect pit diameter and depth, while taking into account the larval body mass.2. Pit diameter increased with larval body mass at a decelerating rate. In addition, larger larvae tended to relocate less frequently than smaller ones.3. Sand depth positively affected overall pit size, while increasing conspecific density had a weaker but negative effect on pit size.4. Feeding the antlions resulted in an increase in pit diameter compared with an unfed control group. However, as prey size increased this positive effect diminished. This result suggests that the existence of prey provides information about the quality of the microhabitat, triggering pit extension. However, similarly to the reduction in the foraging effort of saturated predators, antlions provided with large prey invested only little effort in pit enlargement.5. Antlions were previously shown to be sensitive to prey and conspecific vibrations in the sand. We thus expected the feeding regime of the neighbour to affect antlion behaviour – surrogate of discriminating between local and global shortage of prey. Nevertheless, antlions with fed neighbours (a local prey shortage) did not show different behaviour compared with a control group in which both antlions were unfed (a global prey shortage).

RHINOCEROS AUKLET DEVELOPMENTAL RESPONSES TO FOOD LIMITATION: AN EXPERIMENTAL STUDY

Abstract Seabirds may be particularly vulnerable to neonatal food restriction because their nestling periods tend to be long and parents may not increase foraging effort during times of prey shortage. We performed a captive study of Rhinoceros Auklet (Cerorhinca monocerata) nestlings to identify adaptations for coping with food shortages, as well as possible consequences of early diet restriction on subadult morphology. We tested effects of a ~50% caloric restriction on Rhinoceros Auklet morphological allocation and levels of the stress hormone corticosterone. Rhinoceros Auklets were reared in captivity and provisioned either ~441 kJ per day or ~227 kJ per day of high-quality forage fish until fledging (n = 13 for both treatment groups). Food-restricted Rhinoceros Auklets allocated energy heavily toward skeletal growth at the expense of mass reserves, resulting in fledglings that were proportioned very differently compared to nonrestricted birds—i.e., at 42 days of age, all birds had approximately the sam...

How do the consumption and development rates of the conifer specialist Aphidecta obliterata respond to temperature, and is it better adapted to limited prey than a generalist?

AbstractThis study aimed to address the effect of temperature on the consumption and development rates of Aphidecta obliterata and to compare the responses of Ap. obliterata (specialist) with that of Adalia bipunctata (generalist) to prey limitation. Temperature had a significant and positive effect on the time to egg hatch of Ap. obliterata. The duration of the larval instars was not affected by prey species at 15°C but was significantly shorter, 12.1 days at 20°C compared with 21.1 days at 15°C. The proportion of time spent in each instar, however, was not affected by temperature or prey species, but the duration of the pupal stage was significantly affected by temperature. The average daily consumption of prey aphids increased with instar and was significantly influenced by temperature. There was a significant difference in the length of the pupal stage between coccinellid species but not that of the larval stage. The duration of the larval period increased under conditions of prey shortage. The pupal period of Ap. obliterata was significantly affected by the food regime but not that of Ad. bipunctata. There was a significant interaction between species and food supply on the length of the pupal stage and the larval stage and the final fresh weight achieved by the newly emerged adults. Male adults weighed significantly less than the females in all regimes. Larvae of Ap. obliterata and Ad. bipunctata did not consume any of the alternative prey (Collembola or Psocoptera) provided. There was no significant difference in the consumption of prey between the two coccinellid species. The results suggest that both of these coccinellids are well adapted to low‐density‐specific prey. There were no obvious differences between the two, which would tend to favour either species in an environment of limited prey.

Size‐Dependent Mating Success at Various Nutritional States in the Yellow Dung Fly

AbstractMating success not only depends on genetic quality, but also equally on environmental factors, most prominently food availability. We investigated the interactive effects of nutritional state and body size on mating success and copula duration in yellow dung fly males (Scathophaga stercoraria; Diptera: Scathophagidae) of three body size selection lines in the laboratory in both non‐competitive (single) and competitive (group) situations. Adults require protein and lipids from prey to reproduce, as well as sugars as an energy source for reproductive activity. We expected mating success to decrease with time because of sperm depletion (sugar treatment) and/or energy shortage (water treatment) relative to the control, prey plus sugar treatment. Based on physiological scaling, we also expected large‐line males to become depleted either sooner because of their higher energy and sperm demands, or later because of their more efficient energy use. Average mating success indeed declined over a period of 5–7 d (or 5–15 potential copulations per male), but equally for all food treatments and body size classes. Surprisingly, water‐fed and small‐line males had the highest mating probability in the non‐competitive setting, while in the competitive setting large‐line males had the highest success. Energy‐depleted males showed apparent terminal investment. Small males acquired females more readily but eventually lost them to larger males in the competitive situation. As shown before, copula duration was inversely related to body size and increased with copulation number, independent of food treatment. We conclude that sugar or prey shortage has little effect on mating success in the short term, and does not differentially affect males of different sizes.

Changes in diet and maternal attendance of South American sea lions indicate changes in the marine environment and prey abundance

Behavioural observations were made of South American sea lions Otaria flavescens in Peru to determine whether changes in their diet and maternal attendance patterns reflected physical changes in the marine environment and alterations in the abundance and distribution of prey. The study was conducted during the breeding season between 1998 and 2002, which was a period that encompassed a strong El Nino (1997 to 1998) and a moderate La Nina (1999 to 2001). Observations revealed strong linkages between maternal attendance patterns and the abundance of prey and oceanographic features close to the rookeries. Acute prey shortage during El Nino resulted in females increasing the length of their foraging trips and decreasing the time they spent onshore with their pups. In contrast, shorter times at sea and longer times onshore were observed during the favourable conditions of La Nina when preferred prey (anchovy and squat lobster) were more abun- dant near the rookeries. Pup mortalities increased when females spent more time at sea searching for prey and did not return frequently enough to nurse their pups. A larger diversity of prey species (particularly of demersal fishes) was consumed during El Nino when anchovy and lobster were less available. Females appeared to adjust their diets and maternal attendance patterns in response to annual changes in the abundance and distribution of prey. These observations suggested that diet and maternal responses reflect interannual fluctuations of the unpredictable Peruvian upwelling ecosystem, and implied that South American sea lions may be good indicators of relative changes in the distribution and abundance of marine resources.

Efeito da escassez de presa na sobrevivência e reprodução do predador Supputius cincticeps (Stål) (Heteroptera: Pentatomidae)

O efeito da escassez de presas no desempenho de femeas de Supputius cincticeps (Stal) foi estudado a 24,6 ± 0,7oC, umidade relativa de 80 ± 4% e fotoperiodo de 12h. Larvas de Tenebrio molitor L. foram fornecidas as femeas durante 24h, a cada um, dois, quatro, seis ou oito dias; pedacos de vagem de feijao (Phaseolus vulgaris L.) foram fornecidos em todos os tratamentos de forma continua. A porcentagem de femeas com posturas, o periodo de oviposicao e o numero de posturas, de ovos e de ninfas diminuiram com o aumento do intervalo sem presa. Entretanto, os periodos de pre-oviposicao e de pos-oviposicao aumentaram a medida que o alimento tornou-se menos frequente, enquanto a longevidade e o numero de ovos por postura nao foram afetados pelo regime de presas. Os resultados sugerem uma compensacao entre a longevidade e a fecundidade (reducao da segunda para manter a primeira), o que pode contribuir para o estabelecimento e a sobrevivencia de S. cincticeps em condicoes de escassez de presa.