Adequate Food Resources Research Articles

Effects of prescribed burning on swainson's warbler home‐range size and habitat use

ABSTRACTPrescribed fire is an often‐used tool for managing or manipulating wildlife habitats. However, studies on the effects of prescribed fire on conservation‐priority songbirds are limited. We examined effects of low‐intensity prescribed burns on vegetation structure and composition, and on habitat use of 45 radiotagged male Swainson's warblers (Limnothlypis swainsonii) during the 2008 and 2009 breeding seasons in the St. Francis National Forest in eastern Arkansas, USA. We found that home ranges in areas with extensive burning (>50% burned) were significantly larger ( = 14.4 ha, SE = 3.5, n = 13) than home ranges in areas with partial burning (<50% burned; = 6.1 ha, SE = 1.3, n = 5) and unburned home ranges ( = 8.5 ha, SE = 1.1, n = 27). Burning decreased understory vegetation density, leaf‐litter depth, and cover, but had no effect on density of woody stems, including giant cane (Arundinaria gigantean; a native bamboo that is thought to benefit from fire). Swainson's warblers did not completely avoid burned regions of their home ranges, but individuals selected dense understory habitats in burned and unburned areas, and burning appeared to intensify selection for areas with less‐variable litter depth. Low‐intensity burning appeared to have minimal impacts on Swainson's warbler habitat use, but did result in increased home‐range size, possibly to compensate for burn‐impacted habitat patches and to enable warblers to acquire adequate food resources. Based on our findings, we suggest that high‐intensity fires or frequent burning could have significant negative impacts on Swainson's warbler habitat. Also, prescribed burning alone was not sufficient to restore remnant populations of cane or a dense understory. We suggest management involving canopy openings in combination with low‐intensity fire may more likely promote the development of dense understory habitat, including giant cane preferred by Swainson's warblers and other understory‐dependent birds. © 2015 The Wildlife Society.

Habitat use of bonobos (Pan paniscus) at Wamba: Selection of vegetation types for ranging, feeding, and night-sleeping.

Understanding the habitat requirements of great apes is essential for effective conservation strategies. We examined annual habitat use of a bonobo group in the Wamba field site within the Luo Scientific Reserve, Democratic Republic of the Congo. Using satellite imagery, we categorized the group's ranging area into three forest types: (1) primary and old secondary forest (P/OS), (2) young secondary forest and agriculture (YS/Ag), and (3) swamp forest (Sw). We tracked the group for 1 year (2007-2008) and compared usage of the three forest types for ranging, feeding, and night-sleeping. We also recorded what the bonobos ate and monitored monthly fruit availability in each forest type. The group ranged and fed more often in P/OS and less often in YS/Ag and Sw than expected based on habitat availability. Also, the group slept mostly in P/OS (94% of nights monitored), but also in YS/Ag (1%), and Sw (5%). Fruit availability in P/OS had no significant effect on habitat selection, but the group fed in YS/Ag most often during the two months when fruits in P/OS were least abundant. In June, when fruit of Uapaca spp. (selectively eaten by bonobos) was generally abundant in Sw, the group mostly ranged and slept there. The bonobos fed most often on herbaceous plants in all three forest types. In Sw, the bonobos frequently ate mushrooms. Our results show that semi-open forest with abundant herbaceous plants such as YS/Ag could be an important feeding habitat and may provide fallback food for bonobos when fruits are scarce. Furthermore, Sw can serve seasonally as a main habitat to complement P/OS if adequate food resources and tree nesting opportunities are available. We conclude that bonobos use diverse habitats depending on their needs and we highlight the importance of minor-use habitats for sustaining populations of target species in conservation planning.

Can river management improve the piping plover’s long-term survival on the Missouri River?

The goal of many animal conservation efforts is to improve short-term demography, but there is growing interest in the potential for producing more fit individuals, resulting in long-lasting demographic impacts. The environments that animals experience prior to independence from their parents can have profound, life-long effects on individual fitness and population demography that managers can potentially exploit. Environmental variables can affect fitness directly through early mortality, delayed maturity, reduced probability of recruitment, decreased fecundity, or a combination of these factors. We studied the imperiled piping plover (Charadrius melodus) nesting on the Missouri River to determine if body condition affected their long-term survival, and, if so, whether these factors could be used to improve conservation and management. We captured and measured adult and hatchling piping plovers during the breeding season (April–August, 2005–2012) to obtain measures of condition (mass, wing-chord length, culmen length). We assessed the effect of environmental variables on plover growth, and the effect of chick condition at fledging on subsequent survival as an adult. Plover chicks grew faster and achieved larger body size if they hatched earlier in the season, were exposed to lower density, and were hatched in higher quality habitat compared to other chicks. Plovers that were heavier at fledging had a higher survival rate (as much as 9%) than lighter plovers during their first year as well as in subsequent years, which could make a significant impact on population viability and an individual’s lifetime fitness. Where the factors that affect development are manageable, they offer an opportunity for conservation to capitalize on these long-term effects. For example, habitat creation, restoration, and protection projects should ensure that adequate food resources are available or created not only to maximize reproductive output, but also to improve the condition of offspring where possible.

Trace fossils analysis of fluvial to open marine transitional sediments: Example from the Upper Devonian (Geirud Formation), Central Alborz, Iran

This study integrates ichnological and sedimentological data to interpret depositional environments of the mixed siliciclastic-carbonate fluvial to marine sediments of the Geirud Formation (Upper Devonian) in the central Alborz, northern Iran. Lithofacies analysis shows that these sediments are deposited in fluvial, tidal, shoreface, and shelf environments. Fluvial and tidal deposits are characterized by the presence of bi- to multi-directional cross beddings, reverse directional current ripples, low angle cross beddings, and herringbone cross beddings, with a few scattered Skolithos and Palaeophycus. Shoreface sediments, accumulated in a storm-influenced setting, are characterized by a preferentially interface and low diversity Cruziana ichnoassemblage (Rhizocorallium, Thalassinoides, Palaeophycus, Chondrites, and Ophiomorpha). In contrast to the fluvial-tidal assemblage, the storm-influenced shelf sediments display a highly diversified, mixture of dwelling and feeding forms (Arenicolites, Protovirgularia, Diplocraterion, Palaeophycus, Thalassinoides, Chondrites, and Helminthopsis), reflecting the presence of adequate food resources both in substrate and water column under normal salinity conditions. A fluvial-shelf replacement of the weakly to scarcely bioturbated sediments by the Rhizocorallium-Thalassinoides suite (Cruziana) – Chondrites-Helminthopsis (distal Cruziana) suite from the lower to upper parts of the succession clearly indicates an overall deepening upward in the Geirud Formation. In contrast to the lower part, generally of restricted environment, the upper part of the succession mainly shows open marine conditions. Ichnofabric development is controlled primarily by depositional conditions, e.g., bottom water oxygenation, sediment type, food abundance, and hydrodynamic level, which all exert control on substrate colonization style.

Dietary inequalities of mother–child pairs in the rural Amazon: Evidence of maternal-child buffering?

This paper explores the expected outcome of maternal nutritional “buffering,” namely that children's diets will be more adequate than mothers' diets under conditions of food scarcity. Data on Amazonian mothers and their children, household demography and economics and direct, weighed measures of household food availability and dietary intakes of mother–child pairs were collected from 51 households to address the following research questions: (1) is there evidence of food scarcity in this setting?; (2) are there differences in energy and protein adequacy between children and their mothers?; and, (3) which individual and household-level factors are associated with these mother–child differences in energy and protein adequacy? In this context of food scarcity, we found that the majority of children had more adequate energy (p < 0.001) and protein (p < 0.001) intakes than their mothers. Multivariate OLS regression models showed that of the individual-level factors, child age and height-for-age were negatively associated with maternal-child energy and protein inequalities while maternal reproductive status (lactation) was positively associated with energy inequality. While there were no gender differences in dietary adequacy among children, boys had a larger advantage over their mothers in terms of protein adequacy than girls. Household food availability was related to maternal-child energy and protein inequalities in a curvilinear fashion with the lowest inequalities found in households with extremely low food availability and those with adequate food resources. This is the first study to quantify maternal-child dietary inequalities in a setting of food scarcity and demonstrates the importance of the household context and individual characteristics in understanding the degree to which mothers protect their children from resource scarcity.

Biogeographic patterns and conservation priorities for the dung beetle tribePhanaeini (Coleoptera:Scarabaeidae:Scarabaeinae) inBolivia

AbstractThe New World Phanaeini are the best known Neotropical dung beetle tribe and a conservation priority among the Scarabaeinae, an ideal focal taxon for biodiversity research and conservation.We compiled a comprehensive distributional database for 39 phanaeine species in Bolivia and assessed patterns of species richness, body size and endemism in relation to abiotic variables and species richness and body mass of medium to large mammals across nine ecoregions.Pair‐wise linear regressions indicated that phanaeine richness, mean size and endemism are determined by different factors. In all cases mammal body mass had greater explanatory power than abiotic variables or mammal richness. Phanaeine richness was greater in ecoregions with on average smaller mammals and greater mammal richness. Mean phanaeine size increased with mean body mass of the largest herbivorous and omnivorous mammals. Endemism was greater in ecoregions with on average smaller herbivorous and omnivorous mammals. On average, smaller phanaeines had more restricted distributions than larger species; ecoregional endemism and mean body size were negatively correlated.Large phanaeines probably depend on large mammals to provide adequate food resources. Greater richness of smaller mammal species may allow for greater temporal and spatial resource partitioning and therefore greater phanaeine species richness. Low numbers of large mammal species may favour the persistence of geographically restricted phanaeine species by reducing interspecific competition with larger, more geographically widespread and presumably dominant phanaeines.Cerrado, Southwest Amazonia and Yungas are priority ecoregions for phanaeine conservation due to high total and endemic species richness.

Location and agricultural practices influence spring use of harvested cornfields by cranes and geese in Nebraska

Millions of ducks, geese, and sandhill cranes (Grus canadensis; hereafter cranes) stop in the Central Platte River Valley (CPRV) of Nebraska to store nutrients for migration and reproduction by consuming corn remaining in fields after harvest. We examined factors that influence use of cornfields by cranes and geese (all mid-continent species combined; e.g., Anser, Chen, and Branta spp.) because it is a key step to efficient conservation planning aimed at ensuring that adequate food resources are available to migratory birds stopping in the CPRV. Distance to night-time roost site, segment of the CPRV (west to east), and agricultural practices (post-harvest treatment of cornfields: idle, grazed, mulched, mulched and grazed, and tilled) were the most important and influential variables in our models for geese and cranes. Probability of cornfield use by geese and cranes decreased with increasing distance from the closest potential roosting site. The use of cornfields by geese increased with the density of corn present there during the early migration period, but field use by cranes appeared not to be influenced by early migration corn density. However, probability of cornfield use by cranes did increase with the amount of wet grassland habitat within 4.8 km of the field. Geese were most likely to use fields that were tilled and least likely to use fields that were mulched and grazed. Cranes were most likely to use fields that were mulched and least likely to use fields that were tilled, but grazing appeared not to influence the likelihood of field use by cranes. Geese were more likely to use cornfields in western segments of the CPRV, but cranes were more likely to use cornfields in eastern segments. Our data suggest that managers could favor crane use of fields and reduce direct competition with geese by reducing fall and spring tilling and increasing mulching. Moreover, crane conservation efforts would be most beneficial if they were focused in the eastern portions of the CPRV and in fields as close as possible to both known roosting and large amounts of wet grassland habitats. © 2011 The Wildlife Society.

Nutrition Knowledge and Confidence Levels of Parents of Children With Cystic Fibrosis

Optimal growth and nutrition status predict better lung function and longevity for children with cystic fibrosis (CF). Daily nutrition therapy for children with CF requires adequate food resources, parental knowledge of nutrition and behavior management, and confidence in one’s ability to apply the skills. The Mountain West Cystic Fibrosis Consortium Questionnaire (MWCFC-Q) was designed to identify educational intervention targets to improve the growth and nutrition of children with CF. Parents of children with CF returned 305 anonymous MWCFC-Qs. Data analyzed included household food security, knowledge of nutrition and general CF therapies, and self-confidence in one’s ability to manage components of CF care. Factors associated with food insecurity were reported by 26.3% of respondents. The median accuracy for questions regarding nutrient content of commonly used foods was 71.4% and 57.9% for CF nutrition therapy. Parents’ self-confidence in overall CF management was relatively high at a mean value 8.28 ± 1.22 of 10 possible. However, mean self-confidence in the CF nutrition domain was significantly less than mean self-confidence for the CF-related tasks domain, which included chest physiotherapy and medication administration (7.75 ± 1.56, 8.62 ± 1.24, P &lt; .001, respectively). Parental knowledge of nutrition for CF and confidence in the application of this knowledge can improve the growth and nutrition status of children with CF. Identification of food security issues may enable health care professionals to adjust nutrition interventions and direct families to appropriate food resources. The MWCFC-Q could be useful for designing and testing educational interventions for nutrition management of CF.

Land-use correlates of breeding performance and diet in Tree Sparrows Passer montanus

Capsule Chick diet varies seasonally and between wet and dry habitats, and there is little evidence for a link between habitat type and productivity. Aim To examine the influence of habitat composition and diversity on Tree Sparrow productivity and nestling diet in a wide variety of locations across the UK. Methods Productivity, chick diet and habitat data were collected from Tree Sparrow nestbox colonies by volunteer bird-ringers in 2002. Nestling diet was assessed by identification of invertebrate remains in faecal sacs. Results Clutch size was significantly higher for Tree Sparrows breeding in farmland than for those in wetland colonies. This did not translate into increased productivity. There was no other evidence of any effect of habitat or nestling diet composition on annual productivity. Diet composition varied seasonally, with habitat type and between individual sites. Conclusions Tree sparrows are capable of successful breeding in a range of habitats, where they utilize a wide range of invertebrate prey types. Lack of evidence for a relationship between habitat composition and productivity within this study may be the result of Tree Sparrows on farmland being restricted to areas providing adequate invertebrate food resources. To reduce the probability of Tree Sparrow populations on farmland being limited by chick food invertebrates, conservation measures aimed at population recovery should include the provision of habitats to support a range of high value invertebrate taxa throughout the protracted breeding season. Mechanisms to provide such habitats are already available within existing UK agri-environment schemes.

Stable Isotopes (δD, δ13C, δ15N) Reveal Associations Among Geographic Location and Condition of Alaskan Northern Pintails

Abstract: Information on spring migration routes, geographic linkages among winter, spring, and breeding locations, and potential geographic effects on arrival body condition of northern pintails (Anas acuta) are currently unknown. Through a combination of stable‐isotope measurements of tissues representing different periods of dietary integration and body composition analyses, we examined these linkages for pintails breeding in Alaska, USA. We collected 77 females at 4 locations upon spring arrival. We performed carbon (δ13C), nitrogen (δ15N), and hydrogen (δD) isotope measurements on flight feathers, breast feathers, and whole blood, and we conducted body composition analyses. Inference based on stable‐isotope values in pintail tissues suggests that philopatry to Alaska was strong, as most of the collected females had stable‐isotope values consistent with the boreal forest of Canada or western Alaska and most spring migrating females had whole‐blood values indicating use of a food web in the boreal forest before collection. These patterns highlight the importance of the boreal forest for production and staging of pintails. Breast feather isotope values grown during prealternate molt were variable and covered the currently documented distribution of wintering pintails. Our results indicate associations among specific geographic areas, habitat use, and arrival condition of female pintails settling in Alaska. Females that wintered or staged in coastal habitat (as indicated by elevated δ13C values) arrived with less body fat compared to those that we inferred to have wintered or staged on inland freshwater habitat. Those females we inferred to use coastal areas appeared to rely more heavily on agricultural fields for nutrient acquisition (as indicated by elevated δ15N but low δ13C values). Our results provide the first link between low‐condition females and inferred use of specific geographic areas before arrival. Conservation on wintering grounds should focus on restoration and protection of wetland complexes that provide adequate natural food resources in proximity to coastal systems that are heavily used by wintering pintails. Conservation efforts should also focus on the boreal forest, not only for pintail, but for other boreal‐dependent species such as lesser scaup (Aythya affinis) (JOURNAL OF WILDLIFE MANAGEMENT 72(3):715–725; 2008)

Survival and growth of brown troutSalmo truttaL. embryos and the timing of hatching and emergence in two boreal lake outlet streams

Survival, growth and hatching of brown troutSalmo truttaembryos were studied usingin situincubation experiments in two lake outlet streams in Finland. The experimental design in both streams included an outlet site and a reference site far downstream. The date of hatching was recorded and the Elliott–Hurley model was then used to predict the time of emergence based on water temperature. For data analyses, the incubation period was divided into ‘winter’ (from fertilization to mid March) and ‘spring’ (from mid March until the end of the experiment). Temperature of the large‐lake outlet remained at 1° C through the winter, while in other sites temperature was close to 0° C. In spring, temperature increased more slowly in the large‐lake outlet. The survival of embryos was overall very high, from 83 to 98%, and they were larger in the outlets than in the downstream sites. Embryos hatched at the large‐lake outlet in March, and 3–5 weeks later in the other sites. Although there were considerable between‐site differences in hatching intervals, difference in expected 50% emergence dates of the earliest and latest site was only 4 days. Thus, any growth advantage that the outlet embryos had in winter disappeared by the end of the alevin period. Lake outlets, however, may be important for age 0 year brown trout later during the summer when other stream habitats do not provide adequate food resources.

Rapid export of organic matter to the Mississippi Canyon

Coastal margins, where rivers serve as the dominant control on productivity and delivery of dissolved and particulate materials, have been understudied.The potential importance of certain river‐dominated margins (RiOMars), such as those of the Mississippi River plume, to the global carbon budget is garnering increased attention because of their disproportionate role in transporting terrigenous materials to the ocean [Dagg et al., 2004; McKee et al., 2004].This study concludes that labile (readily open to chemical, physical, or biological change) sedimentary organic matter, produced by in situ diatom production in the Mississippi River plume, is rapidly transported to the Mississippi Canyon. Despite the notion that canyon sediments are typically unstable and lack adequate food resources to support significant macrobenthic communities, this study suggests that productive RiOMars are important conduits for transporting fixed carbon from highly productive plume waters on the shelf to deeper benthic communities.

Long-distance movements of harbour seals (Phoca vitulina) from a seasonally ice-covered area, the St. Lawrence River estuary, Canada

Previous studies of harbour seal (Phoca vitulina L., 1758) movements indicate that this species is relatively sedentary throughout the year. However, few investigations have examined their movements and seasonal distribution patterns in ice-covered areas. This study used spatial analysis of ice data and movement data from harbour seals collected via satellite (n = 7) and VHF radiotelemetry (n = 15) to explore this species' spatial use patterns in a seasonally ice-covered region, the St. Lawrence River estuary, Canada. When solid ice formed within the bays of the estuary, four of the seven satellite-tagged animals (all adult males) left their summer haul-out areas, migrating 266 ± 202 km (range 65–520 km) to over-wintering sites. The seals exhibited preference for areas of light to intermediate ice conditions during the winter months; at least six of the seven seals occupied areas with lighter ice conditions than those that prevailed generally in the study area. Evidence of high abundance of potential prey for harbour seals in the estuary during winter suggests that reduced availability of adequate food resources is not the primary factor which influences the movement and distribution patterns of harbour seals. Movement patterns observed during the ice-free period concur with previously reported harbour seal behaviour; the seals remained near the coast (&lt;6.1–11.0 km from shore) in shallow water areas (&lt;50 m deep in 100% VHF and 90% SLTDRs (satellite-linked time-depth recorders)) and travelled only short distances (15–45 km) from capture sites. None of the VHF- or satellite-tagged seals crossed the 350 m deep Laurentian channel, which suggests that this deep body of water might represent a physical barrier to this coastal population.

Maturation feeding and reproductive development in adult pine weevil, Hylobius abietis (Coleoptera: Curculionidae).

Maturation feeding on conifer bark by newly emerged Hylobius abietis(Linnaeus) is essential for reproductive development. When feeding occurs on young conifer transplants, this weevil causes significant economic damage. Between emergence and oviposition however, weevils feed on bark from different sources but of unknown nutritional 'quality'. The factors influencing the rate of feeding by males and females and female reproductive development were determined in laboratory bioassays using two contrasting food sources - the bark on different species of seedling conifer and on logs of mature trees. The nutritional 'quality' of bark was characterized by the concentration of nitrogen, total sugars, total polyphenols and resin. Regression models were used to show that overall, the rate of feeding on the bark of both seedlings and logs increased with weevil size and was negatively related to nitrogen concentration. The nitrogen concentration in seedling bark (mean 1.1%) was about three times higher than that of logs (mean 0.4%). The rate of reproductive development increased with nitrogen intake during feeding and the preoviposition period for weevils feeding on seedlings and logs was ~ 13 days and 46 days, respectively. Analysis of weevil mortality and of the weight gain of surviving weevils suggests that a nitrogen content of around 0.3% may be limiting for H. abietis. The possibility that nutritionally adequate food resources may be limiting for H. abietis is briefly discussed.

Trace fossil assemblages in a Middle Triassic mixed siliciclastic-carbonate marginal marine depositional system, British Columbia

A diverse ichnofossil assemblage characterizes the mixed siliciclastic-carbonate marginal marine succession of the upper Liard Formation (Middle Triassic), Williston Lake, northeastern British Columbia. Sedimentary facies within this succession consist of five recurring facies associations: FA1 (upper shoreface/foreshore); FA2 (washover fan/lagoon); FA3 (intertidal flat); FA4 (supratidal sabkha) and FA5 (aeolian dune). Shoreface/foreshore sediments (FA1) accumulated on a storm-dominated, prograding barrier island coast and are characterized by a low-diversity Skolithos assemblage (Diplocraterion, Ophiomorpha, Palaeophycus, Planolites, Skolithos and Thalassinoides). Washover fan/lagoonal sediments (FA2) are dominated by trophic generalists. (Cylindrichnus, Gyrochorte, Palaeophycus, Planolites, Skolithos, Trichichnus and an unusual type of bivalve resting trace), consistent with deposition in a setting subject to periodic salinity and oxygenation stresses. Intertidal flat deposits (FA3) are characterized by a diverse mixture of dwelling, feeding, and crawling forms (Arenicolites, Cylindrichnus, Diplocraterion, Laevicyclus, Lingulichnus, Lockeia, Palaeophycus, Planolites, Rhizocorallium, Siphonichnus, Skolithos, Teichichnus, Taenidium, and Thalassinoides, reflecting the presence of adequate food resources in both the substrate and in the water column. Vertical burrow-dominated trace fossil assemblages within thin, sharp-based sand beds are interpreted as intertidal tempestites and reflect post-event colonization of the intertidal zone by shoreface organisms. Supratidal sabkha deposits (FA4) are characterized by an exceptionally low-diversity trace fossil assemblage (Cylindrichnus, Monocraterion and rare diminutive Ophiomorpha). Solution collapse breccia and root traces overprint many primary physical and biogenic sedimentary structures, reflecting numerous cycles of desiccation and flooding. Aeolian dune deposits (FA5) consist of unfossiliferous, exceptionally well-sorted sandstone beds.

Influence of galls ofPhanacis taraxacion carbon partitioning within common dandelion,Taraxacum officinale

AbstractWe examined how leaf galls, induced by the cynipid waspPhanacis taraxaci, influence the partitioning of photoassimilates within the host, the common dandelion,Taraxacum officinale.Galled and ungalled plants were exposed to14CO2and the labelled photoassimilates accumulating within galls and other parts of the host were measured. During the growth phase of the gall they were physiological sinks for photoassimilates, accumulating 9% to 70% of total carbon produced by the host, depending upon the number of galls per plant. High levels of14C assimilation in the leaves of galled plants compared to controls, suggest that galls actively redirect carbon resources from unattacked leaves of their host plant. This represents a significant drain on the carbon resources of the host, which increases with the number and size of galls per plant. Active assimilation of14C by the gall is greatest in the growth phase and is several orders of magnitude lower in the maturation phase. This finding is consistent with physiological and anatomical changes that occur during the two phases of gall development and represents a key developmental strategy by cynipids to ensure adequate food resources before larval growth begins.

Seasonal Water, Energy and Food Use by Free-Living, Arid-Habitat Mammals

In arid ecosystems, the dry season is probably an especially challenging time for animals to find adequate food and water resources. Both stressful and benevolent times of the year can be identified by measuring rates of water and energy use (with doubly labelled water), diet and behaviour throughout a year in free-ranging animals. Such field studies have been completed on four species of arid-land mammals. Jackrabbits (Lepus californicus) are strict herbivores, and most Mojave Desert individuals have no access to drinking water, and depend on their food for their water. When vegetation dries up during the summer drought, most jackrabbits apparently die of dehydration and malnutrition, but populations are replenished by bountiful reproduction after winter rains. However, springbok antelope (Antidorcas marsupialis), also strict herbivores, can maintain water and energy balance throughout the year in the Kalahari in southern Africa by drinking water if available, but, if not, they obtain enough water from dietary plants, probably by feeding before dawn, when food items have taken up water from the humid air. Antelope ground squirrels (Ammospermophilus leucurus) are omnivorous in the Mojave Desert, and are active diurnally. They have lower water and energy requirements than non-desert mammals of the same body mass, like many desert mammals, but their ability to find succulent plant or animal foods in all seasons appears to be their primary survival tool. On the other hand, Merriam's kangaroo rats (Dipodomys merriami) are essentially nocturnal, and were thought to be strict granivores that never drank. A recent study, done throughout a year in the Mojave Desert, confirms their lack of drinking, but reveals that they eat much green vegetation in late winter and spring, probably in connection with reproduction. They obtain additional water throughout the year by caching dry seeds in humid burrows, where seeds take up water hygroscopically before being eaten. Although springbok, antelope ground squirrels and Merriam's kangaroo rats were in negative energy and water balance at times during the year, only jackrabbits were severely stressed by the dry season. Each species has a unique suite of desert survival mechanisms. Future research should include carnivores as well as arid-habitat marsupials.

Herbivorous nutrition of Cyclops vicinus: the effect of a pure algal diet on feeding, development, reproduction and life cycle

Nutritional requirements, functional response, development and reproduction of Cyclops vicinus were studied with exclusively algal food. Phytoflagellates were found to be adequate food resources for both juvenile development and egg production. Ingestion measurements were performed with Chlamydomonas reinhardii . The functional response data give evidence for low feeding efficiency, especially for the naupliar stages. A difference between nauplii and older instars was also found in their quantitative food needs. A higher threshold food concentration was observed for naupliar development (0.4 mg C l −1 ) than for copepodite development (0.2 mg C l −1 ). The calculation of assimilation efficiencies suggests that the high food requirements are due to low specific ingestion rates rather than poor assimilation efficiency. Development time decreased as algal density increased and males developed more quickly than females at all food concentrations. Body size and carbon content increased with increasing food concentration. Continuous egg production was observed above a food concentration of 0.5 mg C l −1 . The results have implications for the life cycle of C. vicinus . Summer diapause is interpreted as a strategy to avoid starvation of the juvenile stages. The facultative herbivory of the adults might be an advantage when competing against other more carnivorous cyclopoid copepods.

A model for territory and group formation in a heterogeneous habitat

We present a simple model for the formation of territories in habitats containing discrete food patches and for the formation of social groups based on these territories. Territories are determined by the distribution of food resources; they are assumed to be as small as is possible while providing adequate food resources for their primary occupants, allowing for the discrete distribution of food, and its variability over time. We show that such territories may often contain sufficient resources to support additional animals at no cost to the primary occupants, especially if individual food patches have a high yield, the variation between patches is large, or the requirements of secondary animals are smaller than those of primary animals. The model thus gives a rigorous basis for the resource dispersion hypothesis of Macdonald (1983, Nature, Lond. 301 , 379–384.) The model predicts that, provided the variation between patches is not too small, the correlation between group size and territory size within such a habitat is likely to be low. The correlation between the amount of resources a territory contains and the size of the group it can support, on the other hand, is likely to be high. In addition, the model predicts that, counter-intuitively, group size does not necessarily increase as the variability of yield over time increases: in some cases, group size may decrease with increasing variability of yield. The main predictions of the model are shown to be unaffected by small changes in parameters, and by changes in some of the model's assumptions.

Community structure of fishes attracted to shallow water fish aggregation devices off South Carolina, U.S.A.

Twenty-two fish aggregation devices were deployed in 14 m of water off South Carolina. Species composition and abundance were determined by diver visual census on eight occasions from May through November, 1985. A total of 21 families and 36 species of fishes was observed at 121 stations. Pelagic fishes dominated the fauna with a 99.3% relative abundance, and Decapterus punctatus accounted for 97.6% of the individuals. Caranx crysos, Diplectrum formosum, Decapterus punctatus, Centropristis striata and Monacanthus hispidus were the most frequent species. Total fish abundance, number of species and abundance of four of the six most common species were significantly affected by season. Hurricane activity may have caused a significant drop in pelagic fish abundance at the FADs in July. No significant correlations among species abundances were found after removal of season and FAD type effects. Spatial zonation and seasonal occurrence patterns suggest some competition among pelagic fishes. Several factors that regulate FAD faunal abundance and composition are hypothesized, including: juvenile fish availability, availability of shelter, availability of adequate food resources, interspecific and intraspecific competition, severe sea conditions, and sporadic intrusions of large predatory fishes. It is hypothesized that the abundances of benthic and pelagic FAD fishes are correlated and that there is a direct or indirect energetic link between shallow water pelagic and benthic fish assemblages near FADs.