Effects Of Food Supply Research Articles

Evaluating the protection of wildlife in parks: the case of African buffalo in Serengeti

Human population growth rates on the borders of protected areas in Africa are nearly double the average rural growth, suggesting that protected areas attract human settlement. Increasing human populations could be a threat to biodiversity through increases in illegal hunting. In the Serengeti ecosystem, Tanzania, there have been marked declines in black rhino (Diceros bicornis), elephant (Loxodonta africana) and African buffalo (Syncerus caffer) inside the protected area during a period when there was a reduction of protection through anti-poaching effort (1976–1996). Subsequently, protection effort has increased and has remained stable. During both periods there were major differences in population decline and recovery in different areas. The purpose of this paper is to analyse the possible causes of the spatial differences. We used a spatially structured population model to analyze the impacts of three factors—(i) hunting, (ii) food shortage and (iii) natural predation. Population changes were best explained by illegal hunting but model fit improved with the addition of predation mortality and the effect of food supply in areas where hunting was least. We used a GIS analysis to determine variation in human settlement rates and related those rates to intrinsic population changes in buffalo. Buffalo populations in close proximity to areas with higher rates of human settlement had low or negative rates of increase and were slowest to recover or failed to recover at all. The increase in human populations along the western boundary of the Serengeti ecosystem has led to negative consequences for wildlife populations, pointing to the need for enforcement of wildlife laws to mitigate these effects.

Effect of food supply on the detoxification in the blue mussel,Mytilus edulis, contaminated by diarrhetic shellfish toxins

The objective of this study was to identify a possible effect of food on the acceleration of decontamination in blue mussels, Mytilus edulis, containing diarrhetic toxins belonging to the okadaic acid (OA) structural group. An experimental protocol was designed to describe and compare the decontamination kinetics and detoxification rates of naturally OA-contaminated mussels that had either received or not received food for three weeks. The protocol was applied in two trials (in June 2006 and June 2007, called Ker06 and Ker07), conducted one year apart on samples of mussels collected in the same area, at the same season. Okadaic acid (OA), the main lipophilic toxin produced by the toxic alga Dinophysis acuminata, was analysed over the course of the decontamination, in hydrolysed (total OA) and non hydrolysed (free OA) digestive gland extracts, in order to estimate acyl-esters (7-O-acyl-ester derivatives of OA) concentrations. OA analyses were also made for toxin presence in biodeposits and in the aqueous phase. Bivalve physiological status was evaluated by biomass measurements (dry weight of flesh) and two biochemical compounds (total lipid and glycogen concentrations). Measured physiological parameters showed that mussels did not suffer under experimental conditions. Both trials showed that the food accelerated the elimination of free and total OA. This effect cannot be attributed to a dilution of the toxin in the tissue, as results expressed in toxin burden led to the same conclusion. The kinetic models of decontamination differed between the two experiments: the model was linear for Ker06, provided that the values corresponding to the first two days were discarded, whereas data fitted a decreasing exponential curve better in Ker07. Detoxification rates increased as the food supply increased. After three weeks of experimentation, the detoxification rates for total OA in Ker06 and Ker07 were 52 and 61%, respectively, in unfed mussels and 90 and 89% in fed mussels (with the highest level in Ker07). Comparisons between the free OA and esters showed that detoxification rate was higher for free OA than for esters, whatever the level of food supply. The results of this study suggest that food increase probably accelerates elimination of OA and OA-esters but the latter are eliminated at a lower speed.

The role of sinking phytodetritus in structuring shallow-water benthic communities

Sinking phytodetritus from surface waters represents a prime source of high-quality food supply for marine benthic organisms. Despite its obvious relevance, the structuring role it plays in shallow sedimentary communities is surprisingly poorly studied. In this article we review the contribution of natural sources of organic food supply to abundance, composition, and diversity of shallow-water macrobenthic communities. We then present a case study that tests how the addition of spring bloom-levels of diatom phytodetritus to a 20-m deep sedimentary habitat contributes to variation in benthic community structure in coastal Newfoundland. In situ patches of otherwise undisturbed sediment were enriched by syringing high and low concentrations of phytodetritus onto their surface. After one week and five weeks, macrofauna in the patches were sampled and compared with ambient sediments where no phytodetritus was added. The experiment was conducted during the summer and then repeated in the fall in order to evaluate how seasonal variation in colonizers might influence infaunal response. Despite significant temporal changes in macrofaunal abundance and composition within and between experiments, the only response that could be attributed to the phytodetritus addition was a rapid response during the first week of the summer experiment. Multiple measures of diversity (species richness, rarefaction, Margalef's index) indicated reduced diversity with phytodetritus addition. These responses did not persist through the five weeks of the summer experiment and were not observed during the fall experiment, suggesting that the effect of food supply is short term and strongly dependent on seasonal timing. In both experiments, the organic material was largely undetectable even after one week. The rapid utilization of phytodetrital patches in shallow-water environments, in concert with higher background levels of phytodetrital flux, may represent a key difference in structuring of shallow-water and deep-sea sedimentary communities.

Effects of food supply on susceptibility of Culex mosquitoes to the fungal biocontrol agent Beauveria bassiana

Effects of food supply on susceptibility of <i>Culex</i> mosquitoes to the fungal biocontrol agent <i>Beauveria bassiana</i>

Variations in Body Size of the Lancelet Branchiostoma belcheri at Different Depths in the Seto Inland Sea: Effect of Food Supply on the Growth Rate

Variations in body size of the suspension-feeding lancelet Branchiostoma belcheri were examined from April 2001 to December 2001 at different water depths of 10-80 m. The lancelets were abundantly collected (220 indiv./dredge) at water depth of 10 m. The maximum size, ranging from 36.8 to 50.4 mm BL, decreased with increasing water depth. However, the minimum size of 7.4-7.8 mm BL, which corresponds to settling size, did not different with water depth. From seasonal changes in the length-frequency histograms, five cohorts were observed at every water depth. The lancelets grew to 44 mm BL at water depths of 10-20 m and to 34 mm BL at water depth of 80 m with four years of life span. Developmental stages of the gonads at an age of two years showed that no individuals had undeveloped gonads at water depth of 10 m, but 82% of them did at water depth of 80 m. The analysis of the stepwise multiple regressions of monthly growth rate on environmental variables showed that chlorophyll a was the best explanatory variable and showed a significant positive correlation with the growth of 1-2 years age groups. These results suggested that variations in the body length were mainly fluctuated by phytoplankton supply.

The effect of food supply and larval cannibalism on adult size and biomass of the grazing caddis‐flyMelampophylax mucoreus(Limnephilidae)

Abstract. 1. Larvae of the grazing caddis‐flyMelampophylax mucoreuswere reared in a laboratory experiment investigating the effect of food availability on different substrates and cannibalism on the size and biomass of emergent adults. All experiments were performed in stream‐water filled, aerated aquaria under controlled temperature and light conditions. Larvae (fourth and fifth instar) were reared in aquaria (50 larvae in each) with three substrate scenarios: (i) limestone (LS), (ii) limestone and leaf litter (LS + L), and (iii) silicate stone (SS).2. Cannibalism among the larvae in the LS scenario led to the highest adult dry masses (male = 5.13 ± 0.25 mg, female = 7.64 ± 0.63 mg) and to the highest mortality rate (88.7%). The SS scenario displayed the most unfavourable condition for larval growth indicated by the lowest adult dry masses (males = 3.12 ± 0.15 mg, females = 4.69 ± 0.25 mg) and a high mortality rate (81.7%). The limestone supplemented with leaf litter (ii) offered the most balanced nutrients to complete larval development and enough shelter to avoid excessive encounter rates of larvae within the aquaria, indicated by the lowest mortality rate (43.6%). Adults from the LS + L scenario showed biomasses (male = 3.94 ± 0.12 mg, female = 6.48 ± 0.24 mg) intermediate between the two other scenarios.3. The results implied that cannibalism among larvae can lead to higher adult biomasses and therefore to increased fitness, if cannibalism supplements larval feeding requirements. Larvae developing under insufficient food availability can not compensate for this by cannibalism. Additionally, leaf litter not only provided a complementary food source for developing larvae, but also provided shelter, which reduced encounter rates.4. Increased stress induced by high larval encounter rates (resulting in enhanced cannibalism) in the LS scenario and low food availability in the SS scenario could be indicated by premature emergence times compared with the LS + L scenario.

Browse site selection by snowshoe hares: effects of food supply and predation risk

If snowshoe hares (Lepus americanus Erxleben, 1777) change their foraging behaviour through the population cycle as food supply and predation pressure change, these shifts could contribute to their population cycles by affecting survival and reproduction. We examined whether hares change their foraging movements and browse site selection in response to manipulations of food addition and predator reduction during a cyclic low phase. Snowshoe hares on sites with supplemental rabbit chow ate fewer species per site and preferred to browse in slightly denser cover than unfed hares. Differences in foraging behaviour were linked to season and site characteristics. Snowshoe hares moved similar distances and spent similar amounts of time per browse site in the presence and absence of terrestrial predators. Hares protected from predators used slightly more browse sites in thick cover, but this pattern was partially due to differences in availability. The absence of terrestrial predators had little effect on snowshoe hare foraging behaviour; instead, browse distribution patterns explained most of the behavioural variation. Thus, the predicted patterns in response to the manipulations did not occur, and our results challenge the idea that changes in snowshoe hare foraging behaviour contribute to their cyclic dynamics.

The effect of food supply on feeding strategy in sessile female gastropods Crepidula fecunda

Sessile females of the gastropod Crepidula fecunda are exclusively suspension-feeders. Our previous work showed that particles removed from suspension are entrained on the gill and continuously accumulate as a mucous string on the distal margin of the lamella, although some are transferred by a ciliary tract to the food pouch, where they form a mucous ball. The mucous string is transferred from the gill margin to the neck canal, where it forms a mucous cord which is transported to the mouth. The mucous ball and the mucous cord are ingested with the aid of the radula. In this study we examined the response of the system to a wide range of cell concentrations of the flagellate Isochrysis galbana. As the particle concentration increased from 5,000 to 200,000 cells ml-1, the volume of the mucous ball almost doubled, as did the number of radular extrusions required to ingest it. The total volume of mucous balls produced and ingested increased very slightly as particle concentration rose from 5,000 to 100,000 cells ml-1, but the volume of mucous cord material ingested increased four to five times over the same range. At higher food concentrations the mucous cord increased in thickness, but not in length, which is constrained by the length of the gill margin. At all particle concentrations the mucous cord accounted for 80–95% of the total material (mucous cords plus mucous balls). Ingestion rate reached a maximum at 140,000 cells ml-1 for mucous balls and mucous cords. At higher concentrations the production of pseudofaeces increased from all sources ("type-I" pseudofaeces from rejected mucous balls; "type-II" pseudofaeces from rejected fragments of mucous cords; and "type-III" pseudofaeces, which come from particles trapped in a coarse mucous net at the mouth of the inhalant mantle cavity and are transferred via the lateral ciliary tract to the mantle margin, by-passing the food pouch). Thus C. fecunda has adopted a feeding strategy in which particle entrainment by the gills is continuous, even at very high ambient particle concentrations (200,000 cells ml-1 for I. galbana), and excess material which cannot be ingested is rejected by one or more of three routes for the elimination of pseudofaeces.

Effect of food supply on development, survival, body weight and reproduction of Nysius huttoni White (Heteroptera: Lygaeidae)

Nysius huttoni White is endemic to New Zealand and a pest oi wheat and brassica crops. Effects of three wild host plant species and sunflower seeds on its development, survival, body weight and reproduction were investigated in this study. On twin cress, N. huttoni developed significantly faster and gained significantly more body weight within a unit time than on shepherds' purse and chickweed, and in development speed and body weight it performed significantly better on shepherds' purse than on chickweed. This bug could develop to adult stage on twin cress and shepherds' purse but females reared from the latter failed to oviposit. The overall survival rate was highest on twin cress among tested plants. Sunflower seeds significantly accelerated sexual maturation and egg production, and significantly increased adult body weight, fecundity and number of viable offspring produced.

Effect of adult feeding on longevity and fecundity of the cigarette beetle, Lasioderma serricorne F. (Coleoptera: Anobiidae).

The effect of food supply on longevity and fecundity of the adult cigarette beetle, Lasioderma serricorne F., was tested under the dark conditions of 30°C and 70% RH. When both males and females were provided with either pollen or water, their mean longevities were almost the same as those of control males and females without a supply of food. On the other hand, if males and females were supplied with both pollen and water simultaneously, their mean longevities were extended about twice as long as those of controls. Both mean oviposition period and mean number of eggs deposited also increased. Females that started feeding on pollen and water before the 7th day after emergence laid nearly equal number of eggs as females feeding throughout their life. When females started feeding on the 9th day, their fecundity increased and oviposition period was prolonged. When mated females were supplied with food together with an oviposition site from just after emergence, their maximum longevity was about 50 d. On the other hand, mated females supplied food without an oviposition site showed a maximum longevity of 80 d. These results suggest that cigarette beetles emigrate from a dry food factory and storage to the field, and feed in the field.

The effect of food supply on metamorphosis and post-larval development in hatchery-reared Pecten maximus

Variations in growth and survival of hatchery-reared post-metamorphic juveniles of Pecten maximus prompted experiments on settlement and post-larval development. The effects of food supply on P. maximus metamorphosis and post-larvae were studied over 4 and 8 week periods. In all experiments, and regardless of the environmental conditions, P. maximus metamorphosed over a 2–3 week period with values of 30% to 50%. After this period, spat numbers increased slightly. Spat mortality was generally low, with values reaching only 10% to 30% after a month of rearing. Mortality increased throughout the second month, however, and reached 50% at the end of some trials. Poor growth was noted when post-larvae were starved for 2 months (10 μm day −1), whereas food levels ranging from 7 to 66 cells μl −1 had a weak influence on post-larval development during the first month (69 to 75 μm day −1) suggesting food requirements of 6000 cells post-larvae −1.

Short‐term and long‐term effects of food supply on parasite burdens in Tawny Owls, Strix aluco

1. The relationships among food supply (Field Voles, Microtus agrestis), reproduction and blood parasites was investigated in Tawny Owls, Strix aluco, in Kielder Forest, Northumberland, in 1994 and 1995. Vole populations were significantly lower in 1995 than in 1994. 2. Birds did not lose parasites after initial infection, and the level at which infections were maintained was characteristic of individual birds. 3. In 1994, the number and intensity of parasites was higher in adult owls that had experienced low food supply when they themselves were reared. This indicated that food supplied to chicks in the nest has a long‐term effect on the parasite burden of adults. 4. In addition, there was evidence that parasite burdens of adults were influenced by their current food supply. Birds that suffered a decline in food abundance on their territories between 1994 and 1995 showed an increase in parasite load over the same period. In 1995, there was also a significant negative correlation between the parasite loads of owls and vole abundance on their territories. 5. The best predictor of parasite number of chicks reared in 1995 was the parasite load of their fathers. The parasites chicks developed were not the parasites with which their fathers were heavily infested. This result could be due to inherited immunity. 6. Our results indicated that food resources should be measured when investigating interactions between parasites and their hosts, and that offspring quality as well as quantity might suffer when food abundance is low.

Influence of food supply and a potential predator ( Crangon crangon) on settling behaviour of plaice ( Pleuronectes platessa)

For many benthic fish species, initial settlement patterns are dependent on the supply of larvae to nursery grounds, and recent work on flatfish population dynamics indicates that larval supply may influence recruitment. After the larvae arrive on the nursery grounds, selection of an appropriate substratum is necessary to maximize their subsequent growth and survival. This paper describes the results of experiments undertaken to determine the behavioural responses of settling plaice, Pleuronectes platessa, to the presence of food and predators. Reared plaice larvae were starved for 24 h, transferred to aquaria and the proportion of time spent on the sediment was recorded in four treatments: no food, benthic food, pelagic food, and benthic + pelagic food. The food supply consisted of newly hatched Artemia as pelagic food and meiofauna extracted from natural sediment as benthic food. Settling behaviour was evident for late stage 3b larvae but there was no effect of food supply on time spent on the sediment. Stage 4b and early stage 5 larvae spent significantly more time on the bottom in the food treatments than in the no-food treatment. No differences could be established between food treatments. In another experiment, with the potential predator Crangon crangon as stimulus, stage 4b and early stage 5 larvae spent significantly more time on the bottom when predators were absent than when predators were present. Behavioural preferences were also studied to establish if benthic food and potential predators, C. crangon, influenced habitat selection. Newly metamorphosed plaice (mean TL 13 mm) were given a choice of sediment with and without food and in a separate experiment, a choice of sediment with and without predators. Plaice spent significantly more time on a sediment with benthic food than on one without food and on a sediment devoid of predators than on one with predators. The habitat selection experiments showed that food supply and predators can influence distribution patterns on a small spatial scale.

Interactive effects of habitat selection, food supply and predation on recruitment of an estuarine fish.

Seagrass meadows are often important habitats for newly recruited juvenile fishes. Although substantial effort has gone into documenting patterns of association of fishes with attributes of seagrass beds, experimental investigations of why fish use seagrass habitats are rare. We performed two short-term manipulative field experiments to test (1) the effects of food supply on growth and densities of fish, and (2) effects of predation on the density and size distribution of fish recruits, and how this varies among habitat types. Experiments were conducted in Galveston Bay, Texas, and we focused on the common estuarine fish, pinfish Lagodon rhomboides. In the first experiment, replicate artifical seagrass and sand plots were either supplemented with food or left as controls. Recruitment of pinfish was significantly greater to seagrass than sand habitats; however, we detected no effect of food supplementation on the abundance of recruits in either habitat. Pinfish recruits in artifical seagrass grew at a significantly faster rate than those in sand habitats, and fish supplemented with food exhibited a greater growth rate than controls in both sand and artifical grass habitats. In our second experiment, we provided artificial seagrass and sand habitats with and without predator access. Predator access was manipulated with cages, and two-sided cages served as controls. Recruitment was significantly greater to the cage versus cage-control treatment, and this effect did not vary between habitats. In addition, the standard length of pinfish recruits was significantly larger in the predator access than in the predator exclusion treatment, suggesting size-selective predation on smaller settlers or density-dependent growth. Our results indicate that the impact of predation on pinfish recruits is equivalent in both sand and vegetated habitats, and thus differential predation does not explain the higher recruitment of pinfish to vegetated than to nonvegetated habitats. Since predators may disproportionately affect smaller fish, and a limited food resource appears to be more effectively utilized by fish in vegetated than in unvegetated habitats, we hypothesize that pinfish recruits may select vegetated habitats because high growth rates allow them to achieve a size that is relatively safe from predation more quickly.

Wintering waterfowl community structure and the characteristics of gravel pit lakes

Wintering waterfowl community structure and their association with lake characteristics were studied in the Cotswold Water Park, a complex of more than 120 gravel pit lakes in southern England. The major distinction in community types was between assemblages dominated by diving waterfowl and those dominated by dabbling waterfowl. The trophic status of lakes was found to be a major determinant of community structure: young lakes in the early stages of a natural process of eutrophication tended to support the most diverse assemblages of diving waterfowl. The abundance of individual species was strongly related to lake size and assemblage type. Some effects of food supply and the recreational use of lakes were also apparent. The relevance of the findings for the sustainable value of the lakes for wintering waterfowl is discussed.

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) x Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The effects of four levels of food supply (0.5%, 1%, 2% and 3% body weight daily) were investigated on some reproductive traits and growth of hybrid tilapia in outdoor concrete tanks. Fast-growing fish matured early in the season (March), but spawning started late in May. Smallest size of males and females at first maturity was 8.1 cm. Fish size at maturity appears to be influenced by the feeding level, which affects the growth of fish. For both sexes, no significant difference was found in gonadosomatic index (GSI) among different treatments. Mean percentage of mature fish decreased with decreasing food supply and was found to be significantly different between fishes fed at 3% (46%) and 0.5% (28%) body weight. Fecundity increased with increased feeding levels, although significant differences were found only between 3% and other feeding rates (0.5–2.0%). The fecundity per g female was higher at the lower ration levels (0.5% and 1%) than at the higher feeding levels. Egg quality, with respect to egg size, hatchability. fry length and weight, was not affected by the feeding rates. Final mean weight and food conversion ratios were significantly influenced by feeding rates. Higher increase in ovary weight with increasing body weight of mature females fed at 0.5% body weight than fishes receiving higher food levels suggests that in these fish, more food resources are diverted towards gonad building than to somatic growth.

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The proximate effects of food supply on intraclutch egg-size variation in American kestrels

Egg size can be an important determinant of offspring survival in birds. We measured eggs from 275 clutches of wild American kestrels (Falco sparverius) to study the degree of intraclutch variability in egg size. We also performed two food-supplementation experiments to investigate the proximate role of food supply during laying in determining egg size. Females with relatively abundant food and those in good body condition did not lay eggs that were more uniform in size than those laid by control females. This result is contrary to hypotheses that propose an adaptive explanation for intraclutch egg-size variation and also to ideas of energy depletion during laying. Patterns of egg size versus laying order were different between years, suggesting that females did not adaptively manipulate laying order and egg size within a clutch. The food-supplementation experiments showed that laying female kestrels probably depend on both stored energy reserves and on daily energy surpluses to form eggs. It appears that slight intraclutch variations in egg size occur in response to short-term food shortages during laying, but that these variations are probably nonadaptive. This is in marked contrast to interclutch (among females) variation in egg size, which we have shown varies significantly with food supply.

Effect of food supply on oyster spatfall

The amount, concentration and type of algae diet supplied to larvae of the European oyster ( Ostrea edulis L.) and the Pacific oyster ( Crassostrea gigas Thunberg) prior to and during spatfall (setting) were varied. Both oyster species gave lower spatfalls when feeding was discontinued immediately prior to settlement. In comparison with control larvae, that were fed a normal diet throughout, 47.7% (range 19–78%) of O. edulis set if the larvae had grown to 295–325 μm (mean shell length) before feeding was stopped but 8.8% (3–16%) if they had only grown to 275–295 μm. Mean spatfall of C. gigas was 10.6% (2–20%) compared with fed controls and, in contrast with O. edulis, was not related to size of larvae, in the range 262–312 μm, at the time that feeding was withheld. The proportionally greater spatfall from larger larvae was related to higher lipid reserves in these larvae, compared with smaller larvae of this species and all C. gigas larvae. O. edulis spat which set in the absence of food contained less lipid and initially grew more slowly than spat which set from fed larvae. Between 95 and 100% of the larvae of both oyster species survived without food for 2 days, but only 20–30% after 6 days. Subsequent spatfall on resumption of feeding was lower than in controls that were fed throughout. This was related to loss in organic weight of surviving unfed larvae of 0.32–0.79 μg over 6 days (15–25% of initial weight when feeding was stopped). This loss was sustained by preferential utilisation of lipid reserves in O. edulis (53–61% of organic weight lost) and protein in C. gigas (about 70% of organic weight lost) during the unfed period. The food requirements for maximum spatfall were estimated as 0.4 μg (organic weight of algae) · larva −1 · day −1 for O. edulis and 0.6 μg · larva −1 · day −1 for C. gigas. With this amount of food per larva available, spatfall at a food concentration as low as 0.035 mg (organic weight of algae) · 1 −1 was similar to that at the control concentration of 1.0 mg ·1 −1. Spatfall was also affected by the nutritional value of the food species supplied during settlement. Algae species known to support slower growth rates of bivalves gave lower spatfalls.

The effect of food supply on the colonisation of barley by aerially dispersing spiders (Araneae).

A field experiment was carried out to determine whether different levels of food availability affected the retention rate of ballooning spiders landing in trays of seedling barley plants, half of which were infested with aphids from laboratory cultures. The trays were placed within bases in the field, then collected sequentially and spider numbers assessed in each tray. Deposition trays, containing trapping fluid only, were used to measure ballooning activity throughout the experimental period. The experiment was repeated four times. Overall, ballooning spiders were more likely to be retained in trays where aphid prey were present, with a total of 340 spiders found in the infested trays and 251 in the aphid-free trays, over the four experiments. Most of the spiders found were of the family Linyphiidae. In the second and fourth experiments the increased retention of spiders in the aphid-infested trays was statistically significant. Immature linyphiids alone also showed significantly higher retention in the infested trays in those two experiments and in the fourth experiment were largely responsible for the higher numbers found in the infested trays. There was also a statistically significant trend for a higher retention rate of female spiders, compared to males, in the barley trays than would have been expected from the ratios of females to males caught in the deposition trapping trays alone.