Are ball-rolling (Scarabaeini,Gymnopleurini, Sisyphini) and tunnelling scarabaeine dung beetles equally choosy about the size of ingested dung particles?

Abstract.  1. The maximum size of ingested particles was determined in 11 species of ball-rolling, adult dung beetle (Scarabaeidae: Scarabaeinae) by mixing small latex or glass balls of known diameter into their food. The tribes Scarabaeini, Gymnopleurini, and Sisyphini (four, four, and three species respectively) were represented, with mean body sizes ranging from 0.33 to 4.0 g fresh weight.
2. Only particles with maximum diameters of 4–85 µm were ingested. Hence rollers, like other known beetles feeding on fresh dung, filter out larger, indigestible plant fragments and confine ingestion to small particles of higher nutritional value.
3. The maximum diameter of ingested particles increased significantly with body weight, whereas taxon (tribe) had no additional effect. Because big rollers accept larger particles than do tunnellers (which make dung stores for feeding and breeding in the soil immediately below the pat) of similar weight, the slope of the diameter-against-weight regression for rollers was significantly higher than that found earlier for tunnellers.
4. An explanation could be that a typical food ball made by a roller is considerably smaller than the amount of dung available to a feeding tunneller of the same size. If the roller were as choosy about particle size as the tunneller, it might not get enough food. This applies to large rollers in particular because their food balls contain a higher proportion of coarse fibres than those made by small species.     

What do dung beetles eat?

Abstract.  1. Most adult coprophagous beetles feed on fresh dung of mammalian herbivores, confining ingestion to small particles with measured maximum diameters from 2–5 to 130 μm, according to body size and kind of beetle. This study explores benefits and costs of selective feeding in a 'typical' dung beetle with a maximum diameter of ingested particles (MDIP) of 20 μm.
2. Examined dung types (from Danish domestic sheep, cattle and horse, and African wild buffalo, white rhino and elephant) contained 76–89% water. Costs of a 20 μm MDIP were often low, since 69–87% of the total nitrogen in bulk dung other than that of elephant and rhino (40–58%) was available to selective feeders.
3. Nitrogen concentrations were high – and C/N ratios low – in most types of bulk dung compared with the average food of terrestrial detritivores or herbivores. Exceptions were elephant and rhino dung with low nitrogen concentrations and high C/N ratios.
4. Estimated C/N ratios of 13–39 in bulk dung (sheep–elephant) were decreased by selective feeding to 7.3–12.6 in the ingested material. In assimilated food, ratios are probably only 5–7, as most assimilable nitrogen and carbon may be of microbial origin. If so, the assimilable food contains a surplus of nitrogen relative to carbon.
5. The primary advantage of selective feeding, particularly in dung with a high C/N ratio, may be to concentrate assimilable carbon in the ingested food. Effects of changing the MDIP within 20–106 μm are modest, especially in dung with a low C/N ratio.     

Role of dung beetle feeding mechanisms in limiting the suitability of species as hosts for the nematode Spirocerca lupi

Various species of dung beetle serve as intermediate hosts after ingesting the embryonated eggs (11–15 × 30–37 µm) of Spirocerca lupi (Spirurida: Spirocercidae) in dog faeces. The feeding mechanisms of coprophagous dung beetles restrict the size of the food particles they can ingest and hence may determine which species can be efficient vectors for S. lupi. In this study, we aimed to exclude certain dung beetle species as possible hosts of S. lupi based on whether or not they ingested latex beads of known diameters mixed into fresh cattle dung. We found that the majority (11/14) of species tested can potentially serve as intermediate hosts of S. lupi because their mouthparts allow the passage of food particles larger than the minimum size range of the eggs of this parasite.     

Abundance and reproductive strategy of the dung beetle Aphodius rufipes (L.) (Scarabaeidae)

Abstract. 1. Adult A.rufipes invade fresh dung pats (mainly in August) and stay for a few days in each pat to feed and oviposit; maximum abundances: 0–100 beetles per cattle dung pat. Larval growth is completed within 40–55 days.
2. The dispersion of beetles is contagious or seemingly random. In sunny weather, with rapid crust formation on the dung, pats deposited in the afternoon are invaded by more beetles than those deposited in the morning.
3. In the field, the total number of eggs per pat is significantly less variable than the number of adult beetles; this might indicate a density-dependent, regulatory, rate of oviposition. The subsequent larval mortality is probably density-independent.
4. Experiments confirmed that the number of eggs laid per female-day in the pats was density-dependent.
5. The non-opportunistic reproductive strategy of A.rufipes may have evolved as an adaptation to life in dung pats: at excessive population densities pats might disappear before completion of larval growth.
6. Finally, A.rufipes in dung pats is compared with blowflies breeding in carrion.     

Getting the most out of waste: how dung beetles boost the nitrogen content in their food

The life cycle of almost all dung beetles revolve around mammalian dung, the feed on dung, look for mating partners on dung and lay eggs in the dung. We know they feed on dung, but we still do not understand how exactly they filter‐feed on the dung and which particles size range they are ingesting. The aim on this study was to investigate the filter feeding by particle selection by adult dung beetles using Scarabaeus goryi and how that improves the nutrient quality of the ingested particles. We compared the particle sizes and nutrient content of the dung with the ingested material in the foregut, hindgut and the faeces of the dung beetle. Adult dung beetles do select smaller dung particles when feeding, we found the maximum particle size for the ingested particle to be around 1400 μm. The average particle size increased through the gut length. Dung beetles also selected particles with higher nitrogen content when feeding, the nitrogen content increased from about 1.5% in the dung to just over 5% in the foregut which then decreased to the level of the unprocessed dung in the dung beetle faeces. Carbon content did not increase from the unprocessed dung to the foregut but decreased through the gut length. Feeding by particle size selection by dung beetles helps in selecting particles with higher nitrogen content to compensate for the low levels found in dung.     

An old adaptive radiation of forest dung beetles in Madagascar

Adaptive radiations of mammals have contributed to the exceptionally high levels of biodiversity and endemism in Madagascar. Here we examine the evolutionary history of the endemic dung beetle tribe Helictopleurini (Scarabaeidae) and its relationship to the widely distributed Oniticellini and Onthophagini. Helictopleurini species are dependent on mammals for their resources. We date the single origin of the tribe at 37 to 23 MY ago, indicating overseas colonization of Madagascar. The main radiation occurred concurrently with the main radiations of lemurs. The ancestors of Helictopleurini are inferred to have been coprophagous species inhabiting open habitats. Subsequent evolution has involved a shift into forests, changes in resource use to a more generalized diet, and changes in body size. Four species of the extant 65 species have shifted to use the dung of the recently introduced cattle in open habitats, allowing these species to greatly expand their geographical ranges.     

Resource utilization by the freshwater deposit feeder Ptychoptera townesi (Diptera: Ptychopteridae)

SUMMARY 1. False crane fly larvae, Ptychoptera townesi (Diptera), occurred in high densities in a flow-controlled section of stream where fine particulate organic matter (FPOM; 0.45 μm to 1 mm in diameter) had accumulated, but were quite rare both upstream and downstream from the section.
2. In laboratory studies, P. townesi grew only on FPOM less than 250 μm. Larvae consistently grew fastest when fed small particles (0.45–53 μm in diameter).
3. Ptychoptera townesi consumed relatively small amounts (0.002 mg per mg animal dry mass day⁻¹) of FPOM (0.45–53 μm). They had long gut content passage times (greater than 19 h) and relatively high efficiencies of conversion of ingested food to body substance (20.7%). Gut content passage times were variable, and depended partially on the nature of the substrate.
4. False crane fly larvae compacted FPOM into faecal pellets considerably larger in size than particles ingested. They lost mass when allowed to feed on their own faecal material, as well as on faeces greater than 250 μm in diameter produced by shredders. However, they survived and grew on shredder faeces (53–500 μm in diameter) that contained a mixture of smaller particles and particles too large for ingestion.
5. The overall pattern of resource utilization by P. townes involved slow handling of relatively small volumes of food, which probably passed once only through a complex alimentary tract.     

Elongated hindguts in desert‐living dung beetles (Scarabaeidae: Scarabaeinae) feeding on dry dung pellets or plant litter

Most adult dung beetles (Scarabaeidae: Scarabaeinae) feed on fresh, wet dung of larger herbivorous or omnivorous mammals. As refractory plant fragments are selected out before ingestion, the food is presumed easily digestible. However, members of the desert‐living scarabaeine genus Pachysoma (probably evolved from an ancestor closely related to the wet‐dung feeding genus Scarabaeus) select dry dung pellets and/or plant litter. Thus, they ingest a much higher proportion of structural plant material, which nevertheless appears to be digested rather efficiently. This study investigates morphological modifications of the gut for this digestion in adults of eight Pachysoma species, both pellet and litter feeders. To ascertain hypothesized ancestral conditions, four fresh‐dung feeding Scarabaeus species were also examined. The latter have the usual dung beetle gut consisting of a long, simple midgut, followed by an equally simple, much shorter hindgut of the same width. Lengths of midguts (M) and hindguts (H) divided by body length (B) for comparison between species of different size are: 4.9–6.3 (M/B) and 0.7–0.8 (H/B), which is normal for dung feeders. In Pachysoma, lengths are 6.3–6.5 (M/B) and 1.0–1.4 (H/B) in pellet feeders, and 4.4–5.0 (M/B) and 2.0–2.5 (H/B) for litter feeders. Hindguts are still morphologically undifferentiated and of midgut width, but clearly longer, particularly in litter feeders. Presumably, plant fragments in the food are digested, at least partly, in the hindgut. If so, the morphological adaptation is unusual: simple elongation rather than the expansion of part of the hindgut, as found in several other plant‐ or detritus‐feeding scarabaeids. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

Intra- and interspecific aggregation of north temperate dung beetles on standardised and natural dung pads: the influence of spatial scale

Abstract.  1. The spatial distribution of north temperate dung beetles ( Aphodius , Sphaeridium , and Margarinotus ) was investigated at three spatial scales (scale  a between all pads – large spatial scale, small patch size; scale  b between block – large spatial scale, large patch size; scale  c within block – small spatial scale, small patch size) in the field using standardised and naturally dropped dung pads that varied in size and volume.
2. Results indicated that all the major colonising species of dung beetle expressed strong intraspecific aggregation, while interspecific aggregation, though present, was of a lesser magnitude.
3. In both controlled and natural dung treatments, intra- and interspecific aggregation decreased with increasing patch size (from pad to block) and also decreased with decreasing spatial scale (from whole plot to within-block scale).
4. The data also suggested that intraspecific aggregation was more important than interspecific aggregation in the distribution of adult dung beetles in natural and standardised dung pads and hence has the potential to facilitate coexistence.
5. Intra- and interspecific aggregation was greater in the natural dung compared with that of the standardised dung, and the effect of pad size partly explains this phenomenon.
6. The within-patch spatial distribution of dung beetles observed in the natural and standardised dung was possibly mediated through within-patch differences between the two treatments. Six confounding factors could explain this difference and these factors are discussed in relation to resource utilisation by north temperate dung beetles.     

Determinants of feeding performance in free-ranging pit-vipers (Viperidae: Ovophis okinavensis): key roles for head size and body temperature

Feeding performance (handling time, capture success) in numerous animal species is well known to be influenced by a variety of ecological, functional, and physiological factors. Nonetheless, few studies have tested which factors are the strongest determinants of animal feeding performance in the wild. Using a field-based experiment, we examined the relationships among a number of functionally important variables and the predatory behaviour of free-ranging pit-vipers ( Ovophis okinavensis ) from Okinawa Island, Japan. Our main findings were: (1) strike latency was negatively related to snake body temperature and, hence, hotter snakes struck at frogs more readily than colder snakes; (2) initial bite position was correlated with ingestion direction (headfirst versus hindfirst) but ingestion direction was not correlated with ingestion duration; and (3) both snake head length and body temperature were negatively related with ingestion duration and, thus, snakes with longer heads and higher body temperatures had shorter ingestion durations. In O. okinavensis , head size and body temperature are therefore likely to have direct ecological consequences in terms of its feeding rate on explosively breeding frogs. More generally, however, this field-based study adds to the growing body of literature demonstrating that temperature has a pervasive influence on the feeding performance of ectotherms in general.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 53–62.     

Diet and food preferences of the endangered Bearded Vulture Gypaetus barbatus: a basis for their conservation

The Bearded Vulture Gypaetus barbatus population in the Pyrenees is managed using feeding stations to increase breeding success and reduce mortality in the pre-adult population. Nevertheless, very little quantitative and qualitative information has been published on such basic aspects of the species' ecology as feeding habits and dietary preferences. This study investigated both aspects through direct and unbiased observation of breeding Bearded Vultures during the chick-rearing period. Bearded Vulture diet comprises mammals (93%), birds (6%) and reptiles (1%), with medium-sized ungulates (mainly sheep/goats) the most important species in the diet (61%, n  = 677). Prey items were not selected in proportion to their availability, with the remains of larger species (cows and horses) being avoided, probably due to the variable cost/benefit ratios in handling efficiency, ingestion process and transport. There is no relationship between the proportion of sheep limbs in the diet and the proximity of feeding stations, suggesting that these sites are probably less important for breeding adults than for the pre-adult population. On the other hand, diet specificity seems related to productivity, with territories with greater trophic breadth being those with higher fecundity. Bearded Vultures prefer to eat limbs, although meat remains (provided principally by small mammals) can play an important role in guaranteeing breeding success during the first few weeks after hatching. The management of carrion provided by animals that die naturally in extensive livestock practices and the remains of wild ungulates which have died naturally or by human hunting, are important conservation tools for the Bearded Vulture and other carrion-eating species.     

Effects of host plant drought stress on the performance of the bird cherry-oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis

Abstract.  1. The growth (increase in height and leaf number) of four grass species was reduced by a −0.5 MPa drought stress, but the performance of an associated herbivore, Rhopalosiphum padi (L.), was not affected consistently. The intrinsic rate of increase of R. padi was reduced by drought stress on three grass species, including Dactylis glomerata (L.), but was unaffected on Arrhenatherum elatius (L.). Therefore, there is no general relationship in the effect of plant drought on an insect herbivore, even among closely related host plant species.
2. Drought stress increased the quality of plant phloem sap, as indicated by increased sieve element osmotic pressure and essential amino acid concentrations. Thus, diet quality could not account for the reduced performance of R. padi under drought stress. The concentration of essential amino acids in the phloem of well-watered A. elatius was, however, lower than that of well-watered D. glomerata , correlating with the decreased performance of aphids on well-watered A. elatius .
3. There were no differences in aphid feeding duration between watering treatments or plant species but sap ingestion rates were reduced significantly under drought stress.
4. Using the measure of dietary amino acid concentrations and the estimate of sap ingestion, the essential amino acid flux through aphids was calculated. Compared with the flux through aphids feeding on well-watered D. glomerata , there was a reduction in aphids feeding on drought-stressed D. glomerata and drought-stressed A. elatius due to lower sap ingestion rates. The flux through aphids on well-watered A. elatius was also reduced due to low phloem essential amino acid concentrations. Thus, the performance of an aphid is correlated with the availability and accessibility of essential amino acids.     

Transient uptake of hypericin by chrysomelids is regulated by feeding behaviour

Abstract. The uptake of hypericin from the foliage of Hypericum perforatum by four species of adult chrysomelid beetles, Chrysolina brunsvicensis , C. geminata, C. hyperici and C. varians , was investigated under laboratory conditions. In no species were detectable levels of hypericin passed from the larval to the pupal or adult stages. The total amount of hypericin found in the adult beetles was positively related to the rate of ingestion of foliage. When feeding activity lessened or ceased, body levels of hypericin declined. In adults of C. brunsvicensis, C. hyperici and C. varians maximal body levels of hypericin occurred after 1–10 days of feeding. In C. brunsvicensis a maximal average level of c. 0.96 μg/beetle was obtained. After 20 days body levels in C. brunsvicensis declined to nearly zero. Adults of C. brunsvicensis contained more hypericin than the other species of beetles, but in no case was enough hypericin sequestered to match the original values (c. 13.3 μg/beetle) published by Rees (1969). Our results caste doubt on the role of hypericin as a sequestered defence against predators.
Analysis of body distribution of hypericin indicated the majority was in the gut lumen (80%). An input-output analysis of hypericin ingested by adults of C. brunsvicensis showed that the greatest majority of hypericin was eliminated in the faeces (up to 85%). Between 15% and 35% of the ingested hypericin was unaccounted for. This loss is the result of a post-defecational degradation of hypericin (perhaps bacterial).     

Herbivore dung as food for dung beetles: elementary coprology for entomologists

1. How do dung beetles and their larvae manage to subsist on herbivore dung consisting of plant remains that are at least partly indigestible, mixed with various metabolic waste products? To clarify what is known and not known about this basic aspect of dung beetle biology, the present review summarises information on dung composition and discusses the feeding of beetles (food: fresh dung) and larvae (food: older dung) in relation to this information. 2. There is 70–85% water in typical fresh dung, and undigested lignocellulose or ‘fibre’ constitutes about 70% of the organic matter which also contains 1.5–3% N. About 75% of this is ‘metabolic faecal nitrogen’, mostly associated with dead and alive microbial biomass. As all essential amino acids and cholesterol are probably present, additional synthesis by microbial symbionts may not be needed by the beetles. 3. Beetles minimise the intake of lignocellulose by filtering fibre particles out of their food which is probably microbial biomass/debris with much smaller particle size. Excess fluid may be squeezed out of this material by the mandibles before ingestion. 4. All larvae are bulk feeders and unable to filtrate, but little is known about the composition of their food, i.e. older dung in pats or underground brood masses. Larvae in dung pats may depend on easily digestible dung components, probably microbial biomass, whereas the nutritional ecology of larvae in brood masses is still not understood. Unravelling the composition of their food might answer some of the so far unanswered questions.     

Payoffs of the two alternative nesting tactics in the African dung beetle, Scarabaeus catenatus

1. Scarabaeus catenatus is a ball-rolling scarab in the subfamily Scarabaeinae. This species, however, makes use of two tactics for nest building: rolling and tunnelling. The tunnelling tactic differs substantially from the rolling tactic in that (1) it always involves repeated movements to and from the dung source and the nest, whereas rolling does not, and (2) it involves a shorter distance between the two sites.
2. Brood-nest founders were usually males and less often females, with about 25% adopting the rolling tactic and 75% adopting the tunnelling tactic. During nest building, the founder paired off with a scarab of the opposite sex, and they co-operated in the work. The female made one to four brood balls from the dung in the nest, each of which contained one egg.
3. Each scarab seemed to be able to employ both tactics. The tactic employed was independent of an individual's status, e.g. body size and timing of nest founding.
4. The rolling tactic offered only male founders a greater nest-defence success than the tunnelling tactic due to a lower intrusion into the rolled nest and a higher intensity of male–male fighting. The tunnelling tactic offered both male and female founders a larger number of brood balls than the rolling tactic because it enabled scarabs to take a larger amount of dung into the nest.
5. The reproductive success for the two tactics was estimated from the product of nest-defence success and the number of brood balls. As a result, the two tactics had equal fitness payoffs for males, but unequal payoffs for females.
6. The results suggest that male alternation of tactics is controlled by a mixed strategy. Female alternation, however, cannot be explained by mixed strategy, alternative strategies or conditional strategy.     

Effects of supplementary feeding on territoriality, breeding success and survival of pheasants

1. The effects of supplementary food in spring on subsequent pheasant breeding in an intensively farmed area in southern England were assessed by a large-scale, replicated field experiment.
2. Territorial cock pheasants were counted in April, and the breeding success and survival of radio-tagged hens were monitored in six 1-km² plots during 1994 and 1995. Total numbers of young reared and post-breeding pheasant densities were found by August counts. In 1994, three randomly selected plots were supplied with wheat grains via hoppers along woodland edges and hedgerows. The other three plots acted as controls and the treatments were reversed in 1995.
3. The density of cock territories increased significantly in food-supplemented plots (44 ± 8 km−2) in relation to control plots (29 ± 8 km−2), and the presence of hoppers significantly affected the locations of territories. However, similar proportions of territorial males acquired harems in the control and food-supplemented plots. Hen density did not increase and, consequently, the mean harem size was significantly lower with supplementary feeding.
4. Hens given supplementary food did not nest earlier and the number of nests initiated, clutch sizes and the proportion of successful nests did not differ significantly from those of controls. However, hens supplied with supplementary food re-nested significantly more quickly following the loss of a nest or brood.
5. Radio-tagged hens did not rear significantly more young with supplementary feeding. Hen survival was unchanged and post-breeding pheasant densities were no higher.
6. On present evidence, spring feeding cannot be advocated as a management technique to improve the breeding success of pheasants surviving the winter.     

Prey size and ingestion rate in raptors: importance for sex roles and reversed sexual size dimorphism

Compared to other birds, most raptors take large prey for their size, and feeding bouts are extended. However, ingestion rate has largely been overlooked as a constraint in raptors' foraging and breeding ecology. We measured ingestion rate by offering avian and mammalian prey to eighteen wild raptors temporarily kept in captivity, representing seven species and three orders. Ingestion rate was higher for small than for large prey, higher for mammalian than for avian prey, higher for large than for small raptors, and higher for wide-gaped than for narrow-gaped raptors. Mammalian prey were ingested faster by raptors belonging to species with mainly mammals in their diet than by raptors with mainly birds in their diet, but the drop in ingestion rate with increasing prey size was more rapid for the former than for the latter. We argue that the separate sex roles found in raptors, i.e. the male hunting and the female feeding the young, is a solution of the conflict between the prolonged feeding bouts at the nest, and the benefit of rapid resumption of hunting in general, and rapid return to the previous capture site in particular (the prey size hypothesis). Thus, the sex roles differ more when prey takes longer to feed, i.e. from insects to mammals to birds. We then argue that the reversed sexual size dimorphism in raptors, i.e. smaller males than females, results from a conflict between the benefit of being small during breeding to capture the smallest items with the highest ingestion rate among these agile prey types (mammals and bird), and the benefit of being large outside the breeding season to ensure survival by being able to include large items in the diet when small items are scarce (the ingestion rate hypothesis). This hypothesis explains the observed variation in reversed sexual size dimorphism among raptors in relation to size and type of prey, i.e. increasing RSD from insects to mammals to birds as prey.     

Re‐establishment of biting mouthparts in desert‐living dung beetles (Scarabaeidae: Scarabaeinae) feeding on plant litter—Old structures reacquired or new ones evolved?

Evolution of mouthparts in adult dung beetles (Scarabaeidae: Scarabaeinae) for eating moist, fresh dung was linked with a loss of the ability to chew. However, the desert‐living genus Pachysoma, probably evolved from a wet‐dung feeding, Scarabaeus‐like ancestor, has switched to a diet of dry fecal pellets (of rodents or small ruminants) and plant litter that requires re‐establishment of chewing. Indeed, gut contents of a litter‐feeding Pachysoma species indicate efficient food comminution. Based on scanning electron microscopy, cutting and grinding mouthpart structures in six Pachysoma species, of two lineages and with different food preferences, are described and compared with homologous structures in wet‐dung feeding Scarabaeus species. In Pachysoma, cutting and breaking of large food items is probably performed by a clypeal scraper, a prominent epipharyngeal tooth and large maxillary galeal hooks. Further comminution is achieved by a large, grinding area evolved on the mandibular molae. Interspecific differences and the probable function and evolution of these structures are discussed. Particularly, the unique tools for cutting/breaking are completely novel structures and not results of some reacquisition of normal biting mouthparts. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Direct and indirect impact of two common rotifer species (Keratella spp.) on two abundant ciliate species (Urotricha furcata, Balanion planctonicum)

1. We investigated the potential competition and feeding impact of the common rotifer species, Keratella cochlearis and K. quadrata , on the abundant prostomatid ciliates, Urotricha furcata and Balanion planctonicum, in laboratory batch culture experiments. All four species have similar feeding preferences, co-occur in many freshwater environments, and are thus potential competitors for the same algal food.
2. Two small Cryptomonas species served as food for the ciliates and the rotifers in the experiments. Growth rates of each ciliate species were measured when they grew alone and when they were paired with one of the rotifer species.
3. Both rotifer species reduced the growth rate of U. furcata , probably primarily by direct feeding on the ciliates. Growth rate of B. planctonicum was unaffected by K. cochlearis , but was drastically reduced by grazing and/or mechanical interference of K. quadrata .
4. These results suggest niche partitioning of the sympatric ciliates with respect to their rotifer competitors/predators.     

Importance of consumptive and non-consumptive prey mortality in a coupled predator–prey system

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina , imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three – nine densities of small or large individuals of each prey species.
2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non-consumptive elements. Non-consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested.
3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non-consumptive mortality (death not followed by ingestion).
4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non-consumptive mortality increased with prey density, although the relationships differed with prey species and size. The non-consumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non-consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes ) or accelerating (small Daphnia ) rate.
5. These results suggest that the importance of consumptive and non-consumptive mortality to total prey mortality needs to be considered when modelling predator–prey dynamics.