Variations in the life-history parameters of Hemipyrellia ligurriens (Diptera: Calliphoridae) in response to larval competition for food

Abstract. 1. Larval rearing densities of Hemipyrellia ligurriens (Wiedemann) (Diptera: Calliphoridae) in standardized carrion were manipulated in order to investigate changes in life-history parameters in response to larval competition for food.
2. Competition was of the typical scramble type. Survivorship remained high at densities up to 32 larvae g liver^-1 but decreased rapidly as larval density increased further.
3. Emergent adults were undersized with reduced fecundity and longevity. Variations in adult body size apparently reduced the effects of competition on larval mortality.
4. Females of dry weight corresponding to only 10.4% of the potential maximum emerged at the highest rearing densities of 128 larvae g liver-1. However, these females had a nearly four-fold increase in reproductive investment (per unit weight) when compared to the largest individuals.
5. The duration of larval development declined when competition was intense (i.e. at high larval densities).
6. The short adult life of H.ligurriens, combined with the unpredictability of larval habitat availability, may reduce the value of long-range dispersal so that females 'do better' by maintaining reproductive investment despite a concomitant decline in dispersal ability.     

Trophic relationships among concentrated populations of small fishes in seagrass meadows

Changes in available food and utilized foods for a densely populated guild of animals can uncover periods of niche displacement among particular consumer species or their separate size classes. Dense populations of small fishes and their foods were çensussed for 13 months and studied experimentally in shoalgrass and turtlegrass meadows of Redfish Bay, Texas. Feeding habits were determined with respect to prey availability, and illustrated the extent to which seasonal partitioning of food corresponded to food depletion among these abundant consumers in seagrass meadow food webs. The darter goby, code goby, pinfish, and Gulf pipefish were the most common species throughout the year. Although the darter goby did not show distinct ontogenetic changes in food habits, the code goby, Gulf pipefish, and pinfish demonstrated major ontogenetic progressions of foods selected.Food availability in the seagrass meadows changed seasonally. When major prey such as amphipods were abundant, during spring, many fish species showed high overlap in food use. Regardless of food availability, the code goby and Gulf pipefish fed mainly on amphipods or copepods. The more common darter goby and pinfish seasonally changed their diets with changes in food availability; the darter goby and pinfish were more carnivorous during spring, but they largely consumed epiphytic algae during summer. Cage experiments were used to monitor foods confined with elevated densities of pinfish and darter gobies, relative to control cages at natural overall densities. Prey items in the former cages decreased sharply, with corresponding dietary shifts by these common fishes. During resource depletion, these changes in resource use by these naturally concentrated consumers appeared as temporary partitioning of available resources. This shift occurred during both natural (seasonal) and experimental depletions of food, and appears to result from increased interspecific and intraspecific competition during periods of depleted preferred foods.     

Consumer versus resource control and the importance of habitat heterogeneity for estuarine bivalves

The relative influence of consumers (top down) and resources (bottom up) on the distribution and abundance of organisms remains a key question in ecology. We examined the relationships between consumer and resource variables along a productivity gradient for a dominant predator–prey interaction in a marine soft‐sediment system. We 1) quantified density and size of the clam Macoma balthica (prey species) in six replicate sites at each of four habitat types (shallow mud, deep mud, muddy sand and detrital mud) in the Rhode River, Chesapeake Bay. We selected one habitat type of high food availability and clam density (shallow mud) and another of low food availability and clam density (muddy sand) for manipulative experiments. Then, we 2) measured M. balthica survival and growth through transplants, 3) measured food availability as sedimentary organic carbon content, 4) quantified predator density, and 5) calculated predator foraging efficiency in the two habitat types. Clam density in the four habitat types differed and was related to sedimentary carbon availability and predator density. One of the habitats, detrital mud, appeared to be a population sink because it only held juvenile Macoma that never survived to reproductive age. Macoma size and growth, and predator (mainly blue crab Callinectes sapidus) densities were positively correlated with productivity and were higher in shallow mud than muddy sand. In contrast, Macoma mortality, local ‘interaction strength’, and predator foraging efficiency were lower in the productive habitat (shallow mud). Thus, predation intensity was inversely correlated with productivity (food availability); consumer and resource effects differed by habitat type; and, at a relatively small spatial scale, consumer and resource forces jointly determined population dynamics in this soft‐sediment marine system.     

Effects of habitat disturbance and food supply on population densities of three primate species in the Kakamega Forest, Kenya

While habitat disturbance and food availability are major factors thought to determine the abundance of primates, evidence for their importance is uneven. We assessed the effects of these factors on three monkey species, guerezas ( Colobus guereza ) , blue monkeys ( Cercopithecus mitis ) and redtails ( Cercopithecus ascanius ), in four areas of the Kakamega Forest, Kenya. Group densities of guerezas and blue monkeys were higher in areas where disturbance levels were also higher. Food availability measured as basal area density of food trees did not correlate significantly with the group densities of any of the three monkeys. The diversity of food trees, another potential measure of food abundance did, however, correlate with group densities of guerezas and blue monkeys suggesting that food availability may positively influence monkey density, and may sometimes increase with disturbance. Group densities of redtails did not correlate with any habitat variable examined, suggesting that factors other than those we considered may have influenced the abundance of this species particularly.     

Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India

Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in relation to habitat. Predictions of hypotheses relating animal density, rainfall, habitat structure, and breeding seasonality, to changes in chital group size were assessed simultaneously using multiple regression models of monthly data collected over a 2 yr period in Guindy National Park, in southern India. Over 2,700 detections of chital groups were made during four seasons in three habitats (forest, scrubland and grassland). In scrubland and grassland, chital group size was positively related to animal density, which increased with rainfall. This suggests that in these habitats, chital density increases in relation to food availability, and group sizes increase due to higher encounter rate and fusion of groups. The density of chital in forest was inversely related to rainfall, but positively to the number of fruiting tree species and availability of fallen litter, their forage in this habitat. There was little change in mean group size in the forest, although chital density more than doubled during the dry season and summer. Dispersion of food items or the closed nature of the forest may preclude formation of larger groups. At low densities, group sizes in all three habitats were similar. Group sizes increased with chital density in scrubland and grassland, but more rapidly in the latter—leading to a positive relationship between openness and mean group size at higher densities. It is not clear, however, that this relationship is solely because of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard antler) was positively related to mean group size in forest and scrubland, probably reflecting the increase in group size due to solitary males joining with females during the rut. The fission-fusion system of group formation in chital is thus interactively influenced by several factors. Aspects that need further study, such as interannual variability, are highlighted.     

A minimalist approach to the effects of density-dependent competition on insect life-history traits

Abstract  1. Due to its effects on the phenotypic and genotypic expression of life-history traits, density-dependent competition is an important factor regulating the growth of populations. Specifically for insects, density-dependent competition among juveniles is often associated with increased juvenile mortality, delayed maturity, and reduced adult size.
2. The aim of the work reported here was to test whether the established phenotypic effects of density-dependent competition on life-history traits could be reproduced in an experimental design requiring a minimal number of individuals. Larvae of the mosquito Aedes aegypti were reared at densities of one, two, or three individuals per standard Drosophila vial and in six different conditions of larval food availability. This design required relatively few individuals per independent replicate and included a control treatment where individuals reared at a density of one larva per vial experienced no density-dependent interactions with other larvae.
3. Increased larval densities or reduced food availability led to increased larval mortality, delayed pupation, and the emergence of smaller adults that starved to death in a shorter time (indicating emergence with fewer nutritional reserves).
4. Female mosquitoes were relatively larger than males (as measured by wing length) but males tended to survive for longer. These differences increased as larval food availability increased, indicating the relative importance of these two traits for the fitness of each sex. The role of nutritional reserves for the reproductive success of males was highlighted in particular.
5. This minimalist approach may provide a useful model for investigating the effects of density-dependent competition on insect life-history traits.     

Wild reindeer foraging-niche organization

Part 1: Diet selection was studied on free-ranging reindeer fitted with an esophageal fistula (EF) and by analysis of rumen samples from reindeer shot in the field. Plant density was assessed from quadrats on field plots. Three measures of palatability were used, the nitrogen, fiber, and total non structural carbohydrate (TNC) contents of samples from clipped vegetation. As lichen density decreased the EK reindeer included progressively more vascular litter and pieces of winter dormant species in their diet. Diets with highest TNC and N/F and the lowest fiber, providing the most readily digestible diets, were selected. The combined density-quality criterion gave the best prediction of their diets. In summer, forbs, and to some extent grasses and dwarf shrubs, were selected. Plants of highest density and in an early growth phase gave the best prediction of summer diets. In winter the variety of vascular plants utilized increased with increasing herd size and decreasing density of lichens in the vegetation. The width of diets was a function of diversity of available plants. It is suggested that dietary selection by reindeer has been a three stage process: evolution of a gastro-intestinal system capable of digesting lichens containing secondary compounds, behavioural tracking of the plant production pulse, and diet width scaling according to density-quality of all potential foods. Part 2: Wild reindeer closely followed the wave of vascular plant production in spring and summer with a significant correlation being found between the daily foraging time per habitat type and the highest concentration of green phytomass. Snow-bed meadows were the most consistently selected vegetation type by the four herds studied, viz. Hardangervidda, Snøhetta, Prudhoe Bay, and Svalbard, during the summer. Habitat niche-breadths were narrow during the winter, largely due to the limitation of access to the food supply by the snow-cover, broadened as the landscape became clear of snow, narrowed again with the initiation of plant growth and broadened once more as the wave of plant production reached all habitat types. At high levels of food resources the alpine herd (Hardangervidda) narrowed the feeding niche breadth (or adopted a selective feeding strategy) as the habitat niche breadth increased. The high arctic herd (Svalbard) living in the least productive environment, at the same time of year adopted a generalist feeding strategy as their habitat niche breadth expanded. Part 3: In this part the temporal organization of a low-alpine herd of reindeer (Hardangervidda) is described, and subsequently compared with those of two arctic herds. Their foraging efficiencies under different degrees of food availability were analysed, in order to test the hypothesis that food intake changes in response to the prevailing state of the food resources. The number of daily feeding bouts increased from 2 to 6 as the diet changed from the winter to the summer pasturage. Strong winds in winter and insect harassment in summer severely depressed the daily time spent foraging. When these environmental factors were accounted for no significant inter-seasonal differences in daily foraging time of the low alpine herd were found; on average 50% of each day was spent grazing, of which 78% of the time was spent on actual ingestion (feeding rate). The feeding rate within the active periods varied with the snow-depth, due to the need to dig a food crater in the snow and due to the particular selective feeding strategy adopted. The data from the present and from other studies suggest that the foraging efficiency of wild reindeer, expressed as their daily food intake follows a Holling type II functional response as food availability changes. Part 4: Sheep is the only sympatric ruminant which grazes with the reindeer on alpine pastures in Norway. The inter-specific niche relationships ot the wild reindeer and the domestic sheep in summer were studied on part of the western Hardangervidda. to test the hypothesis of inter-specific competition. Three niche dimensions were meas-ured, diel, habitat utilization, and spatial distribution. The estimates of the degree of overlap obtained suggest that this is relatively high for diet and habitat utilization but low for spatial distribution, which leads to a low degree of foraging interference. Since the intensity of both interspeeific and intra-specific competition depends on the ratio of the herbivore densities to the food resource density, the degree ol overlap in utilization by the two species tell us nothing about the degree of competition. Present numbers of both species on Hardangervidda have a beneficial influence on the vegetation, by opening-up the shrub-layer canopy and thus facilitating the main-tenance of grasses and forbs in the field layer, which has a higher carrying capacity for ruminants. The balance between the beneficial effects and inter-generic competition (if any) deriving from the present-day stocking rales is so tar unknown. Only long-term monitoring of the performance of both populations will shed light on this competitive aspect.     

Demographic responses of adult Mesocyclops thermocyclopoides (Copepoda, Cyclopoida) to different plant and animal diets

1. We studied the effects of food type on adult females of the cyclopoid copepod Mesocyclops thermocyclopoides.
2. The test diets, covering a size range of 5–1250 μm, included a toxic strain of Microcystis aeruginosa , three algae (i.e. Chlorella vulgaris, Scenedesmus acutus and Chlorogonium elongatum ), three ciliates (i.e. Tetrahymena pyriformis, Stylonychia notophora and S. mytilus ), two rotifers (i.e. Brachionus angularis and B. calyciflorus ) and two cladocerans (i.e. Ceriodaphnia cornuta and Moina macrocopa ), and a selected subset of them in a second experiment.
3. Experimental diets were started with the last juvenile instar (C5) and data were collected on the newly moulted adult females. The survival of the copepod was less affected by food type than its reproductive output. Net reproductive rate was significantly higher with animal than with plant food. Algal diets enriched with organic extracts supported higher reproductive rates than unenriched diets of the same algal species. The large and motile alga Chlorogonium gave performances which approached those of ciliate diets.
4. The pre-reproductive period of M. thermocyclopoides was shorter and its post-reproductive period longer with animal than with plant diets, the latter being chiefly caused by a briefer period between clutches.
5. The frequency of infertile clutches increased in later clutches, indicating possible sperm limitation in females which have mated only once.
6. There was a significant, positive correlation between the size of food particles and the lifetime reproductive output of M. thermocyclopoides , with more than an order of magnitude difference in the total fecundity between the largest and the smallest food items.
7. Mesocyclops thermocyclopoides achieved the highest total fecundity with 'mixed' food, and thus, reflected the adaptive value of omnivory for this species.     

Floristic heterogeneity between forested sites in Kibale National Park, Uganda: insights into the fine-scale determinants of density in a large-bodied frugivorous primate

1.  Despite a long history of research on the influence of fruit availability on the population density of large-bodied vertebrate frugivores, operational understanding of the factors regulating density in these taxa remains elusive. We propose that fruit resources can be distinguished from one another on the basis of their functional role for the animals in question, and that such a classification system can aid in identifying the most influential determinants of frugivore density.
2.  We compared the availability of several resource classes between two sites in Kibale National Park, Uganda separated by only 12 km yet differing threefold in density of chimpanzees ( Pan troglodytes ).
3.  We categorized plant species used for fruit by chimpanzees according to their availability relative to habitat-wide fruit productivity, and by their tendency towards inter-individual fruiting synchrony. We predicted that the site of high chimpanzee density would support a higher density of food plant species tending to produce crops during periods of high habitat-wide productivity [high fruit abundance (HFA foods)] and of those tending to fruit synchronously among individuals during times of low habitat-wide availability (sLFA foods). The first food class should provide chimpanzees with a high nutrient density (and thus promote population growth), whereas the second should provide stable subsistence during lean periods and thus a temporally consistent resource base.
4.  Counter to our prediction, only sLFA resources were more abundant at the site of high chimpanzee density than at the site of low density. We suggest that sLFA resources are most important in influencing density of large-bodied frugivores.     

Allometry of territory size and metabolic rate as predictors of self-thinning in young-of-the-year Atlantic salmon

1. Self-thinning is a progressive decline in population density caused by competitively induced losses in a cohort of growing individuals and can be depicted as: log₁₀ (density) = c − β log₁₀ (body mass).
2. In mobile animals, two mechanisms for self-thinning have been proposed: (i) the space hypothesis predicts that maximum population density for a given body size is the inverse of territory size, and hence, the self-thinning slope is the negative of the slope of the allometric territory-size relationship; (ii) the energetic equivalence hypothesis predicts that the self-thinning slope is the negative of the slope of the allometric metabolic rate relationship, assuming a constant supply of energy for the cohort.
3. Both hypotheses were tested by monitoring body size, population density, food availability and habitat for young-of-the-year Atlantic salmon ( Salmo salar ) in Catamaran Brook, New Brunswick. The results were consistent with the predictions of the space hypothesis. Observed densities did not exceed the maximum densities predicted and the observed self-thinning slope of −1·16 was not significantly different from the slope of −1·12, predicted by the allometry of territory size for the population under study.
4. The observed self-thinning slope was significantly steeper than −0·87, predicted by the allometry of metabolic rate, perhaps because of a gradual decline in food abundance over the study period. The decline in density was more rapid in very shallow sites and may have been partly caused by a seasonal change in water depth and an ontogenetic habitat shift rather than solely by competition for food or space.
5. The allometry of territory size may be a useful predictor of self-thinning in populations of mobile animals competing for food and space.     

Breeding ecology of the endemic Black Lark <Emphasis Type="Italic">Melanocorypha yeltoniensis</Emphasis> on natural steppe and abandoned croplands in post-Soviet Kazakhstan

Since the collapse of the Soviet Union in 1991, the abundance and distribution of many central Asian steppe birds have been affected by changes in agricultural land management, such as the abandonment of large areas of cropland and changing grazing patterns. However, the underlying population processes that drive patterns of abundance and distribution are poorly understood. We compared the population ecology of the Black Lark Melanocorypha yeltoniensis on natural steppe and abandoned cropland. Between 2009 and 2013, we used distance sampling to quantify Black Lark population density, monitored 220 nests to assess reproductive performance, and modelled habitat selection at several scales. Arthropod food availability was compared using pitfall traps. Mean population densities were three times higher on abandoned cropland compared to those in steppe, and varied with time since abandonment. Nest survival rates were significantly lower on abandoned cropland compared to steppe, probably due to higher predation pressure. Chick growth rates were also lower on abandoned cropland, despite higher insect availability in this habitat. Habitat selection was strongly influenced by grazing intensity and vegetation structure. We suggest that Black Larks are generally attracted to abandoned cropland because of its suitable vegetation structure and higher food availability. The results of a fecundity model suggested that the number of breeding attempts on abandoned cropland necessary to produce the same number of fledglings as one nesting attempt in steppe habitat was 2.04 in 2011 and 3.62 in 2013. However, a phenological analysis revealed that there were only two peaks in first egg dates, making more than two re-nesting attempts per year unlikely. Therefore, abandoned cropland could, at least in some years, be an ecological trap for the species. Our results illustrate that the effects of land-use change on animal populations should not only be assessed using species densities, but also incorporate detailed demographic analyses. If current densities in steppe habitat corresponded to maximum carrying capacity, overall population densities of Black Larks are likely to decline in the near future as availability of abandoned cropland as nesting habitat is currently decreasing.     

Enhanced niche opportunities: can they explain the success of New Zealand's introduced bird species?

Aim  The niche hypothesis could explain why some species introduced to new locations reach higher densities than in their native range: it posits that the new environment provides more abundant or higher quality resources or habitat, a more suitable physical environment or both. We investigate whether 11 bird species occur at higher densities in their introduced range than in their native range and whether the differences can be explained by the availability of preferred habitat or the suitability of climatic conditions in their introduced range relative to their native range.
Location  South Island, New Zealand (the introduced range); UK (the native range).
Methods  We first develop a series of models that accurately predict the density of 11 bird species at 54 UK farmland sites, which are closely matched to our New Zealand sites, from habitat and climatic variables. We then use these models to predict the density of the 11 species at 54 New Zealand farmland sites and compare the predicted and observed values.
Results  Actual densities at New Zealand sites were on average (median) 22 times (range: 1–6361) higher than predicted from the UK models and similarly higher than actually observed at comparable UK sites. Habitat and climatic variables can accurately predict bird densities in the UK but grossly underestimate densities for all species except Turdus merula in New Zealand.
Main conclusions  These findings indicate that factors other than the measured habitat and climatic variables must differ between the two regions and explain the much higher densities of New Zealand birds. We suggest that introduced birds, other than T. merula , in New Zealand may still experience enhanced niche opportunities due to greater availability of higher quality resources within habitats, release from natural enemy regulation, less exposure to extreme weather events, particularly during winter, or some combination of these processes.     

Resource utilization by two insular endemic mammalian carnivores,the island fox and island spotted skunk

We compared resource utilization of two insular endemic mammalian carnivores, the island spotted skunk and island fox, along niche dimensions of space, food, and time on Santa Cruz Island. We predicted that resource use by foxes and skunks would differ along one or more niche dimensions, and that both species would have broader niches or higher densities compared with mainland relatives. Island foxes and island spotted skunks differed to some extent in habitat use, diets, and circadian activity, which may account for their long-term coexistence. Nonetheless, substantial overlap between skunks and foxes in spatial, dietary, and temporal dimensions suggests that competition between the two species does occur. Moreover, competition may be asymmetric, affecting skunks more than foxes. Compared with mainland foxes, island foxes have smaller body size, smaller home range, increased population density, increased diurnal activity, and behavior that is more highly inquisitive and less flightprone all common features of insular faunas. Island skunks, however, apparently have not developed these changes, perhaps due to asymmetric competition with foxes in conjunction with severe ecosystem disturbances caused by feral sheep.     

Seasonal Food Use Strategies of <Emphasis Type="Italic">Semnopithecus vetulus nestor</Emphasis>, at Panadura and Piliyandala,Sri Lanka

Field studies on Semnopithecus vetulus have shown high folivory and the ability to feed heavily on mature leaves, which are constantly available. In research spanning 19 mo, I examined the feeding behavior of 2 free-ranging groups of Semnopithecus vetulus nestor in home gardens and rubber monocultures at Panadura (PT1 group) and Piliyandala (R1 group), Sri Lanka. Overall, results showed that >80% of their diet comprised seasonal plant parts, largely fruits. Despite differences in spatial and temporal food availability in their respective habitats, seasonal plant parts dominated the diets of both groups except briefly (2 mo) for R1 when mature leaf petioles were the main plant food. Both groups increased their use of seasonal foods with heightened seasonal food availability, and increased dietary diversity with declining use of their highest-ranked specific item of diet: fruits of Artocarpus heterophyllus (jakfruit, Moraceae). PT1, which was in a species-rich environment, maintained a high intake of seasonal foods year round by exploiting a large number of species, mainly for fruits. In contrast, R1, in a habitat with significantly lower tree species richness, had a less diverse diet but maintained an equally high intake of seasonal foods, primarily fruits and seeds, by exploiting a few species heavily. My study also highlights the dietary flexibility of a single colobine species in space and time. Such information is useful for conservation planning because rapidly occurring changes are taking place in natural colobine habitats.     

Diet and activity pattern of howler monkeys (Alouatta palliata) in Los Tuxtlas, Mexico: effects of habitat fragmentation and implications for conservation

Accelerated deforestation is causing the rapid loss and fragmentation of primary habitat for primates. Although the genus Alouatta is one of the most studied primate taxa under these circumstances, some results are contradictory and responses of howlers to habitat fragmentation are not yet clear. In this paper, we conduct a cross-study of the available researches on mantled howlers (Alouatta palliata) in forest fragments in Los Tuxtlas, Mexico, to (1) describe the diet and activity pattern of howlers; (2) analyze the similarity in the diet across studies; and (3) relate both fragment size and howler population density with different characteristics of their diet, home range size, and activity pattern. Howlers consumed 181 plant species belonging to 54 families. Ficus was the most important taxa in the howlers' diet, followed by primary species such as Pterocarpus rohrii, Nectandra ambigens, Poulsenia armata, and Brosimum alicastrum. Secondary and non-secondary light-demanding plant species, which are representatives of disturbed habitat, contributed with a high percentage of their feeding time. Only 23% of the species consumed were the same across all the studies, suggesting that howlers adapt their diet to the food availability of their respective habitats. Population density is the best predictor of howlers' ecological and behavioral changes in response to forest fragmentation, probably owing to its relationship with food availability. Howlers respond to the increase in population densities by increasing the (1) diversity of food species in the diet; (2) consumption of non-tree growth forms; and (3) consumption of new plant items. Home range size is also predicted by population density, but fragment size is a better predictor, probably owing to the fact that howler groups can overlap their home ranges. Our results emphasize the importance of conserving the larger fragments and increasing the size of small and medium-sized ones.     

Seasonality of reproduction by liverbearing fishes in tropical rainforest streams

Reproductive ecology, population structure, and diets of three common livebearing poeciliid fishes (Alfaro cultratus, Phallichthys amates, Poecilia gilli) from rainforest streams in Costa Rica were investigated over ten continuous months. The region experiences little annual temperature variation, and although monthly rainfall is continuous each year, two brief dry seasons typically occur. Monthly changes in indices of ovarian condition, percentages of females with developing embryos, and population size structure revealed that reproductive output by females of all three species varied seasonally. Based on testicular condition, males were reproductively active year-round, however the mean gonadal index for males of two algivorous species showed low levels of seasonal cycling that largely coincided with female variation in reproductive effort. All three species had seasonal differences in the female size-brood size relationship, whereby larger females tended to carry more embryos during the wet season. Several important adult and neonate food resources are more available in the flooded forest during the wet season, which is also the period when conspecifics and predators are at their lowest per-area densities. Three hypotheses are discussed: (1) brood size in relation to conspecific density-mating frequency, (2) reproductive allocation in response to variation in adult food resources, and (3) selection for greater reproductive effort during conditions optimal for juvenile growth and survival. Data for Alfaro were consistent with the latter two hypotheses. In Phallichthys and Poecilia, diets were poorer during wet seasons, indicating that reproductive effort does not coincide with availability of adult food resources, and that selection probably favors greater reproductive effort during periods optimal for juvenile growth and survival.     

Does availability of anthropogenic food enhance densities of omnivorous mammals? An example with coyotes in southern California

To evaluate whether the abundance of coyotes Canis latrans was influenced by the availability of anthropogenic foods in a humanized landscape, we compared three neighboring areas (hereafter referred to as NA, CA, and SA) under contrasting human pressures within the Santa Monica Mountains of California, USA. We quantified the use of anthropogenic foods by coyotes and assessed local densities within these three regions. Overall, 761 coyote feces were analyzed; identified food items were categorized into 11 food types (7 native and 4 anthropogenic). Though small mammals (lagomorphs and rodents) were the main prey of coyotes in all areas and seasons, log‐linear modeling of multiway contingency tables indicates that consumption of anthropogenic foods by coyotes varied significantly throughout study areas. Thus, in the most humanized area (CA; 24% of this region is residential habitat), anthropogenic foods (trash, livestock, domestic fruit) comprised seasonally between 14 and 25% of total items in coyote diets, whereas in the least humanized area (NA; 2% residential) anthropogenic foods only comprised seasonally between 0 and 3% of items. Coyote density, estimated by foot‐hold trapping surveys and by genotyping feces, was also highly variable between areas. The heavily human‐impacted CA area had the highest coyote density (2.4–3.0 ind. km^?2), whereas coyote density was significantly lower (0.3–0.4 ind. km^?2) in the least humanized area (NA). In the third region (SA; 10% residential), with an intermediate level of human pressure, both importance of anthropogenic foods in coyote diet (4–6%) and coyote density (1.6–2.0 ind. km^?2) were intermediate compared to the other regions. Our data suggest that subsidization by anthropogenic foods augments coyote densities and alters their diets in the Santa Monica Mountains, California. We include data from literature to show that anthropogenic foods are used by omnivorous mammals throughout the world. Surprisingly, however, the potential effects of allochthonous inputs on such species are not well‐understood. Thus, further research on this phenomenon in humanized landscapes is needed.     

Effect of resource gradient on age and size at maturity and their influence on early‐life fecundity in the predatory Asian lady beetle,Harmonia axyridis

Variation in food availability impacts the performance of insects in terms of their size and age to maturity and fecundity. Age at maturity determines how quickly individuals in a population can start to reproduce and how much they can reproduce. Results from studies on various insect species show that food availability influences the size and fecundity of adult females. It is predicted that under poor growth conditions, variation in size is low, but variation in age at maturity is considerable. This prediction was examined in a widely distributed lady beetle species, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), a predator of aphids and coccids. Using a food gradient from low to high aphid prey density, performance of females that were reared on excess food was recorded for pre‐reproductive duration, size at reproductive maturity, number of aphids consumed, and fecundity in the first 10 days of their reproductive period. Results suggested that female H. axyridis that were reared on surplus food when kept at low prey density (poor growth condition) took, on average, three times longer to attain maturity and produced, on average, 14 times fewer eggs than females that were also reared on surplus food, but kept at high prey density (good growth condition). Females performed best at a prey density of 30 aphids per female per 150 cm². Results suggested that the current food availability significantly influenced the age and size of females at maturity and their fecundity. Age and size at maturity of female lady beetles showed non‐linear responses to prey density as well as the occurrence of a minimum size of females, below which H. axyridis females fail to mature. The steep slope recorded at lower prey densities suggests relatively high variation in age at maturity but low variation in size.     

Feeding of tropical freshwater fishes: seasonality in resource availability and resource use

Summary Food resources in the environment and in the diets of small fish inhabiting two water bodies in a tropical savanna were studied during both wet and dry seasons. During the wet season (high water, abundant food) most fish species in both habitats fed predominantly on vegetation-dwelling invertebrates. Most fish species switched to alternative foods (algae and detritus) following the drastic decline in invertebrate food available towards the end of the dry season. In one habitat, this change in diet was accompanied by an increase in the volume of food intake. In the second habitat, only two larger species foraged intensively, while smaller species showed low food intake or almost ceased feeding. These differences may be explained by the high risk of predation for small fish in the second habitat. Dietary overlaps among fish species were high at the end of the dry season and moderate in the wet season. However, critical analysis of such factors as food abundance, the size and number of shared prey, and diet breadth showed that all significant overlaps were ecologically unimportant i.e. there was only weak competition for food.     

Moose density and habitat productivity affects reproduction,growth and species composition in field layer vegetation

Question: What is the effect of a gradient in moose density on reproduction, growth and functional composition of the field layer vegetation in a boreal forest, and how is this effect modified by habitat productivity? Location: Northwest of Umeå, Västerbotten, northern Sweden. Methods: Field layer vegetation was surveyed in an experimental setup with simulation of three different moose densities and a control in eight study sites along a gradient of habitat productivity. Results: We found that increased moose density led to decreased cover and reproductive effort of a browsed dwarf shrub (bilberry, Vaccinium myrtillus L.) and increased cover and reproductive effort of a non‐browsed graminoid (wavy hair‐grass, Avenella flexuosa (L.) Drejer). Increased moose density led to increased light availability and probably reduced competition from V. myrtillus. Total reproductive effort in the field layer vegetation increased, height decreased and cover of light‐demanding species and graminoids increased with increasing moose density. The effects of moose density were modified by the productivity gradient, leading to a higher relative increase in light availability and reproductive effort in highly productive areas than in low productive areas. Conclusions: Increased light availability was an important indirect effect of moose density, leading to less competition for light and a shift towards early successional species. The effect of moose density on light availability was modified by habitat productivity, leading to stronger relative effects in highly productive areas than in low productive areas.