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Flower size and number usually evolve under pollinator-mediated selection. However, hot, dry environments can also modulate display, counteracting pollinator attraction. Increased pollen deposition on larger flower displays may not involve higher female fitness. Consequently, stressful conditions may constrain flower size, favouring smaller-sized flowers. The large-flowered, self-incompatible Mediterranean shrub Cistus ladanifer was used to test that: (1) this species suffers pollen limitation; (2) pollinators are spatially-temporally variable and differentially visit plants with more/larger flowers; (3) increased visits enhance reproduction under pollen limitation; (4) stressful conditions reduce female fitness of larger displays; and (5) phenotypic selection on floral display is not just pollinator-mediated. We evaluated pollen limitation, related floral display to pollinator visits and fruit and seed production and estimated phenotypic selection. Flower size was 7.2-10.5 cm and varied spatially-temporally. Visitation rates (total visits/50 min) ranged from 0.26 to 0.43 and increased with flower size. Fruit set averaged 80% and seed number averaged 855, but only fruit set varied between populations and years. Selection towards larger flowers was detected under conditions of pollen limitation. Otherwise, we detected stabilizing selection on flower size and negative selection on flower number. Our results suggest that selection on floral display is not only pollinator-dependent through female fitness in C. ladanifer. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176, 540-555. [ABSTRACT FROM AUTHOR]

Native bee abundance has long been assumed to be limited by floral resources. This paradigm has been established in large measure because more bees are often found in areas supporting greater floral abundance. This could result from attraction to resource-rich sites as well as greater local demographic performance in sites supporting high floral abundance; however, demographic performance is usually unknown. Factors other than floral resources such as availability of nest sites, pressure from natural enemies, or whether floral resources are from a mixed native or mostly monodominant exotic assemblage might influence survival or fecundity and hence abundance. We examined how the survival and fecundity of the native solitary bee Osmia lignaria varied along a gradient in floral resource abundance. We released bees alongside a nest block at 27 grassland sites in Montana (USA) that varied in floral abundance and the extent of invasion by exotic forbs. We monitored nest construction and the fate of offspring within each nest. The number of nests established was positively related to native forb abundance and was negatively related to exotic forb species richness. Fecundity was positively related to native forb species richness; however, offspring mortality caused by the brood parasite Tricrania stansburyi was significantly greater in native-dominated sites. These results suggest that native floral resources can positively influence bee populations, but that the relationship between native floral resources and bee population performance is not straightforward. Rather, bees may face a trade-off between high offspring production and low offspring survival in native-dominated sites. [ABSTRACT FROM AUTHOR]

Within a community, species may germinate at different times so as to mitigate competition and to take advantage of different aspects of the seasonal environment (temporal niche differentiation). We illustrated a hypothesis of the combined effects of abiotic and biotic competitive factors on germination timing and the subsequent upscale effects on community assembly., We estimated the germination timing ( GT) for 476 angiosperm species of the eastern Tibetan Plateau grasslands under two light treatments in the field: high (i.e. natural) light and low light. We also measured the shift in germination timing ( SGT) across treatments for all species. Furthermore, we used phylogenetic comparative methods to test if GT and SGT were associated with seed mass, an important factor in competitive interactions., We found a significant positive correlation between GT and seed mass in both light treatments. Additionally, small seeds (early germinating seeds) tended to germinate later and large seeds (late germinating seeds) tended to germinate earlier under low light vs high light conditions., Low light availability can reduce temporal niche differentiation by increasing the overlap in germination time between small and large seeds. In turn, reduced temporal niche differentiation may increase competition in the process of community assembly. [ABSTRACT FROM AUTHOR]

Savannas are highly heterogeneous tree-grass mixtures, and the structural variation imposed by a discontinuous canopy cover results in spatial variation in soil properties such as plant-available nutrients, temperature and soil moisture. Many savannas are also dominated by large vertebrate herbivores, which impose a different suite of effects on soil properties related to consumption, excretion and physical disturbance., In nutrient-poor, water-limited systems, variation in soil resource availability may play a fundamental role in structuring plant communities, but the relative and interactive effects of key drivers of heterogeneity have received little attention in savanna ecosystems., We investigated the independent and interactive effects of herbivores and tree canopy cover on multiple soil properties up to a depth of 10 cm, including bulk density, soil C pools, total and plant-available nutrients, moisture dynamics and temperature at two contrasting sites in Kruger National Park, South Africa. We analysed samples from locations under and between adult tree canopies and inside and outside long-term herbivore exclosures using a nested design., We found strong positive effects of tree canopies on total and labile pools of soil C and N and negative effects on plant-available P and soil temperature. Tree canopy effects on soil moisture availability were small but clearly detectable. During precipitation events, trees increased moisture inputs on granite soils but decreased moisture inputs on basalt soils compared to open sites., Conversely, we found mixed evidence for herbivore effects on soil chemistry and temperature, but a clearer effect on soil moisture, with areas outside exclosures experiencing higher soil moisture retention, particularly immediately following precipitation events. Soil bulk density, a driver of both nutrient and soil moisture dynamics, was lower under trees and when herbivores were excluded., Synthesis. Our results suggest that variation in tree cover is the dominant biotic driver of C, N and P dynamics in these savanna systems in the top 10 cm of soil, that herbivores primarily affect soil moisture content, and that canopy and herbivore effects tend to be additive rather than synergistic. [ABSTRACT FROM AUTHOR]

Resource availability and quality determine the distribution and community structure of animals in ecosystems. However, the balance between energy supply and energy consumption of species has received little attention because of the difficulty of estimating these factors. We measured the carrying capacity of a stream ecosystem in relation to the metabolic demands of Banded Kokopu (Galaxias fasciatus), a drift-feeding fish, to investigate the proportion of their energy budget met by the supply of their primary prey, drifting invertebrates. We sampled drifting invertebrates from multiple pools in 2 freshwater streams once a month over 1 y and measured their energy content. We used the energy content of individual invertebrates to estimate the total energy available in the form of drifting invertebrates in each pool. We measured fish O2 consumption rate (mg O2 kg-1 h-1) and converted it to metabolic demand (cal/h). Drifting aquatic invertebrates alone appear to be insufficient to meet Banded Kokopu energetic requirements in most seasons because the fish could obtain up to only 60% of their total energy expenditure from this food source. This result indicates that Banded Kokopu must access other sources of energy, such as benthic food items or terrestrial invertebrate inputs, especially during episodic events, and highlights the potential importance of terrestrial-aquatic exchange and other energetic subsidies. Our results suggest that food supply is likely to limit assemblages of drift-feeding fish and plays a key role in determining the outcome of intraspecific interactions, growth, movement, and the distribution of individuals within streams. [ABSTRACT FROM AUTHOR]

In disease ecology, there is growing evidence that environmental quality interacts with parasite and host to determine host susceptibility to an infection. Most studies of malaria parasites have focused on the infection costs incurred by the hosts, and few have investigated the costs on mosquito vectors. The interplay between the environment, the vector and the parasite has therefore mostly been ignored and often relied on unnatural or allopatric Plasmodium/vector associations., Here, we investigated the effects of natural avian malaria infection on both fecundity and survival of field-caught female Culex pipiens mosquitoes, individually maintained in laboratory conditions. We manipulated environmental quality by providing mosquitoes with different concentrations of glucose-feeding solution prior to submitting them to a starvation challenge. We used molecular-based methods to assess mosquitoes' infection status., We found that mosquitoes infected with Plasmodium had lower starvation resistance than uninfected ones only under low nutritional conditions. The effect of nutritional stress varied with time, with the difference of starvation resistance between optimally and suboptimally fed mosquitoes increasing from spring to summer, as shown by a significant interaction between diet treatment and months of capture. Infected and uninfected mosquitoes had similar clutch size, indicating no effect of infection on fecundity., Overall, this study suggests that avian malaria vectors may suffer Plasmodium infection costs in their natural habitat, under certain environmental conditions. This may have major implications for disease transmission in the wild. [ABSTRACT FROM AUTHOR]

The benthic filamentous green algal (FGA) community of Saginaw Bay, Lake Huron, has not been extensively examined, despite its apparent link to shoreline fouling. The objective of this study was to elucidate factors, including light, nutrients, and substrate, expected to affect grovifth of FCA. We examined the FGA community in the southwest region of the bay, which started -5 km northwest from the Saginaw River, a known source of nutrients and sediment. Cellular nutrient quotas and photosynthetic parameters were measured in FGA over a range of water column depths and distances from the Saginaw River and then compared to published thresholds of limitation. Our results suggest that light limitation sets the maximum depth of growth and prevents growth near the Saginaw River. Our data also indicate that a light gradient extends from the Saginaw River into our study area, but we did not observe direct evidence for the existence of a parallel nutrient gradient Most of the FGA community experienced both light and P stress, with the exception of 20% of the sampled FGA, which experienced saturating levels of midday light Nitrogen deficiency was never observed. Our results suggest that post-dreissenid invasion increases in water clarity extended the maximum depth limit for FGA from -3.3 to -5 m, greatly increasing the area of FGA growth. One quarter of sampled FGA were strictly P-limited and 87-100% of sampled FGA were P-deficient, suggesting that phosphorus-based management approaches could successfully reduce FGA growth in inner Saginaw Bay [ABSTRACT FROM AUTHOR]

Comparing animal consumption to plant primary production provides a means of assessing an animal's impact on the ecosystem and an evaluation of resource limitation. Here, we compared annual fruit and leaf consumption by Japanese macaques ( Macaca fuscata) relative to the annual production of these foods in the lowlands and highlands of Yakushima Island, Japan. We estimated consumption by macaques by the direct observation of macaque groups for 1 year in each habitat. We estimated leaf production as the sum of leaf litter fall (corrected for the effect of translocated organic and inorganic matter) and folivory by insects (assumed to be 10%) and by macaques. We estimated fruit production as the sum of fruit litter fall and consumption by birds (estimated by the seed fall) and macaques. The impact of macaque folivory at the community level was negligible relative to production (∼0.04%) compared with folivory by insects (assumed to be 10%); however, for some species, macaque folivory reached up to 10.1% of production. Tree species on which macaques fed did not decline in abundance over 13 years, suggesting that their folivory did not influence tree species dynamics. For the three major fleshy-fruited species in the highland site, macaques consumed a considerable portion of total fruit production (6-40%), rivaling the consumption by birds (32-75%). We conclude that at the community level, macaque folivory was negligible compared with the leaf production, but frugivory was not. Am. J. Primatol. 76:596-607, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Late-acting (ovarian) self-incompatibility, characterized by minimal or zero seed production following self-pollen tube growth to the ovules, is expected to show phylogenetic clustering, but can otherwise be difficult to distinguish from early-acting inbreeding depression. In Amaryllidaceae, late-acting self-incompatibility has been proposed for Narcissus ( Narcisseae) and Cyrtanthus ( Cyrtantheae). Here, we investigate whether it occurs in the horticulturally important genus Clivia ( Haemantheae) and test whether species in this genus experience ovule discounting in wild populations. Seed-set results following controlled hand pollinations revealed that Clivia miniata and C. gardenii are largely self-sterile. Self- and cross-pollinated flowers of both species had similar proportions of pollen tubes entering the ovary, and those of C. gardenii also did not differ in the proportions of pollen tubes that penetrated ovules, thus ruling out classical gametophytic self-incompatibility acting in the style, but not early inbreeding depression. Flowers that received equal mixtures of self- and cross-pollen set fewer seeds than those that received cross-pollen only, but it was unclear whether this effect was a result of ovule discounting or interactions on the stigma. The prevention of self-pollination by the emasculation of either single flowers or whole inflorescences in wild populations did not affect seed set, suggesting that ovule discounting is not a major natural limitation on seed production. Flowers typically produce one to three large fleshy seeds from approximately 16 available ovules, even when supplementally hand pollinated, suggesting that fecundity is mostly resource limited. The results of this study suggest that Clivia spp. are largely self-sterile as a result of either a late-acting self-incompatibility system or severe early inbreeding depression, but ovule discounting caused by self-pollination is not a major constraint on fecundity. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 155-168. [ABSTRACT FROM AUTHOR]

This study aimed to determine the functional seasonal attributes for herbivores of the major habitats and landscapes of the Savuti-Mababe-Linyanti ecosystem (SMLE) of northern Botswana and how various herbivore species responded to this heterogeneity. Floodplain grasslands and dambo grasslands provided the only significant green forage and biomass during the late dry season, whereas short grasslands of the Mababe Depression provided the highest forage quality of all habitats during the wet season. The ability to provide reliable forage and drinking water in floodplain, swampand dambo grasslands attracted large concentrations of zebra and buffalo during the dry season, which was mediated by fire. Large concentrations of zebra were observed in mineral-rich grasslands of the Mababe Depression during the wet season, whereas buffalo were not observed in these open grassland landscapes in this season. Other herbivore species appeared to use the same landscapes year-round where lechwe were observed mainly in floodplain and swamp landscapes on the western edge of the Linyanti Swamps, while wildebeest and impala were observed in floodplains and adjacent woodlands near permanent water suggesting that these species had access to sufficient resources at a landscape scale. Thus various herbivore species responded differently to functional heterogeneity across seasons and scales. [ABSTRACT FROM AUTHOR]

We used exogenous application of a phytohormone (gibberellin GA3, ' GA') to test the hypothesis that common perennial grasses may not be growing at all times to the limit of resource availability. Plants were taken from the field in winter, and again in summer and their responses to GA assessed under standard conditions, indoors, to reveal their 'potential' for growth at different times. Time of year, and associated developmental state, had a major impact on the capacity of plants to respond to exogenous GA, and less so their current growing conditions, temperature and N availability, during measurement. A major increase in dry matter ( DM) production in winter-derived plants took place at both low and high N, with no evidence of a reduction in N content in tissues. That ryegrass plant growth can be stimulated, without externally adding resources, supports the hypothesis there is an element of internal control in how plants respond to 'signals' in their environment, that might be manipulated. This offers prospects for reducing environmental impacts (leaching, N2 O) compared with obtaining the same yield increase by adding fertilizer N in early season. Responses to exogenous GA were detected (as significant) but far smaller in summer-derived plants. Molecular mechanisms of detection of N resource signals, developmental triggers and the role of endogenous gibberellin need to be unravelled to assess scope for breeding ryegrass germplasm to better match demands for increased production with greater resource-use efficiency. [ABSTRACT FROM AUTHOR]

The formation of tree-cavities is an important ecological factor since many animals in woody habitats are cavity users. Recent research focuses on tree-cavity formation and the associated cavity networks in forest ecosystems. However, although traditional European orchards are important habitats for secondary cavity users, ecological research on the factors associated with the occurrence of cavities in fruit trees is widely missing. In particular, fruit tree pruning management may affect decay-cavity formation due to the pruning wounds allowing heart rot and decay to enter the tree. Here, we present a cross-sectional study investigating 608 fruit trees in 30 study plots of three European fruit-growing regions to identify factors associated with decay-cavity occurrence in fruit trees. Presence of decay-cavities was positively related to trunk diameter. Moreover, fruit trees of low vitality and with woodpecker-cavities featured more often decay-cavities than trees of high vitality or without woodpecker-cavities. Apple trees featured higher numbers of cavities at younger age than other fruit trees. Occurrence of decay-cavities was also related to the past removal of large main branches. Accordingly, traditional orchards are cavity-rich habitats if they comprise high proportion of old fruit trees, in particular apple trees, and if pruning management produces large pruning wounds. Thus, differential tree pruning and fruit-growing traditions across Europe result in different cavity densities in traditional orchards. Preservation of existing and potential cavity trees and selective removal of large branches from apple trees are recommended as conservation measures establishing high cavity densities and increasing the associated biodiversity in the agricultural landscape. [ABSTRACT FROM AUTHOR]

Because we found previously that Chlamydomonas reinhardtii produces allelochemicals to which the rotifer Brachionus calyciflorus is sensitive, we explored its effects on other freshwater plankton. We used Chlamydomonas under light-, nitrogen- and phosphorus-limitation to test its allelopathic effect on Microcystis aeruginosa, Cryptomonas ozolinii, Ochromonas danica, Tetrahymena thermophila and Paramecium aurelia. Allelopathy depended strongly on the target organism. Only Cryptomonas suffered a marked negative effect. Among the resource limiting regimes, light limitation exerted the greatest effect. [ABSTRACT FROM PUBLISHER]

Almost all models of plant resource limitation are grounded in either one or both of two simple conceptual models: Liebig's Minimum Hypothesis (LMH), the idea that plants are limited by the resource in shortest supply, and the Multiple Limitation Hypothesis (MLH), the idea that plants should adjust to their environment so that all essential resources are equally limiting. Despite the differences in their predictions, experiments have so far failed to discriminate between them. In a simple factorial nitrogen and water addition experiment in a Minnesota grassland, we observed shifts in allocation that, as in previous studies, are not all explained by a single theory. We found that leaf biomass responded positively to nitrogen additions but did not respond to water additions. We found that fine-root biomass increased in response to water additions, but only at low nitrogen levels, and that fine-root biomass decreased in response to nitrogen additions, but only at high water levels. To understand these responses we built a physiologically based model of plant competition for water, nitrogen, and space to predict plant allocation to fine roots and leaves. Critically, we include in our model the inherent variability of soil moisture and treat light, water, and nitrogen as resources with distinct mechanistic roles. Experimental results showed that plants were nitrogen and water limited. The model explains the experimental results, under conditions of co-limitation, as follows. Foliage increases with nitrogen additions but not water additions because leaf construction is constrained by nitrogen uptake. When water is added, plants spend a larger fraction of the growing season limited by light (and effectively nitrogen) than by water. Thus, water additions cause fine-root biomass to increase because of the increased importance of nitrogen limitation. The response of fine-root biomass to water additions decreases with nitrogen additions because these additions reduce nitrogen limitation. In general, our results are explained by sequential resource limitation. The rate of carbon assimilation may be limited by a single resource at any one moment, but the identity of the limiting resource(s) changes throughout the growing season. [ABSTRACT FROM AUTHOR]

Population density can have profound, often negative effects on fitness-related traits and population dynamics, and density dependence is of central importance to many prominent ecological and evolutionary hypotheses. Here, we used experimental manipulations of food, population density, and water conditioning to characterize the mechanisms underlying reproductive density-dependence in Potamopyrgus antipodarum. This New Zealand freshwater snail is a prominent model system for invasion biology, ecotoxicology, and the maintenance of sexual reproduction. We demonstrated that a primary source of negative density-dependence is food limitation, but surprisingly, we found that P. antipodarum reproductive output was much higher in high density versus low-density conditions when food was adequate. We then used manipulations of water environment to demonstrate that these positive effects of high density are likely caused by a waterborne substance produced by P. antipodarum. Altogether, these results indicate that there are strong and complex connections between food availability, density, and reproductive output in this important model system that could influence the dynamics of invasive populations, the costs and benefits of sex, and the approaches used for ecotoxicology studies. [ABSTRACT FROM AUTHOR]

Although adaptive plasticity would seem always to be favored by selection, it occurs less often than expected. This lack of ubiquity suggests that there must be trade-offs, costs, or limitations associated with plasticity. Yet, few costs have been found. We explore one type of limitation, a correlation between plasticity and developmental instability, and use quantitative genetic theory to show why one should expect a genetic correlation. We test that hypothesis using the Landsberg erecta × Cape Verde Islands recombinant inbred lines (RILs) of Arabidopsis thaliana. RILs were grown at four different nitrogen (N) supply levels that span the range of N availabilities previously documented in North American field populations. We found a significant multivariate relationship between the cross-environment trait plasticity and the within-environment, within-RIL developmental instability across 13 traits. This genetic covariation between plasticity and developmental instability has two costs. First, theory predicts diminished fitness for highly plastic lines under stabilizing selection, because their developmental instability and variance around the optimum phenotype will be greater compared to nonplastic genotypes. Second, empirically the most plastic traits exhibited heritabilities reduced by 57% on average compared to nonplastic traits. This demonstration of potential costs in inclusive fitness and heritability provoke a rethinking of the evolutionary role of plasticity. [ABSTRACT FROM AUTHOR]

Outbreeding confers an evolutionary advantage, and flowering plants have evolved a variety of contrivances for its maximization. However, neither fruit set nor seed set is realized to its fullest potential for a variety of reasons. The causes of low flower to fruit and seed to ovule ratios were investigated in naturally occurring bael trees ( Aegle marmelos) at two sites for three seasons. The study established that the mass effect of synchronized flowering attracted a variety of insect pollinators to the generalist flowers; Apis dorsata was the most efficient pollinator. The seed to ovule ratio was low despite high natural pollination efficiency ( c. 2400 pollen per stigma). Although pollination-induced structural and histochemical changes in the style allowed many (9.5 ± 2.1) pollen tubes to grow, only cross-pollen tubes could grow through the style. Gametophytic self-incompatibility, manifested in the stylar zone, resulted in a significantly slower growth rate of self-pollen tubes. The occurrence of obligate self-incompatibility, coupled with increased self-pollen deposition (geitonogamy), caused a significant number of flowers to abort. Fruit retention in the trees declined from 40% to 12% as a result of abortion of fruits at different stages of development. The number of mature fruits on a tree was negatively correlated ( r = −0.82) with their size. It is inferred that low natural fecundity in A. marmelos is primarily a result of obligate self-incompatibility and strong post-fertilization maternal regulation of allocation of resources to the developing fruits. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172, 572-585. [ABSTRACT FROM AUTHOR]

Optimal timing of reproduction is critical to ensure adequate conditions for raising young. However, factors influencing timing of reproduction may differ between sexes. Harsh seasonal environments offer unique opportunities to link timing with resource availability and strategies of the sexes. The Arizona gray squirrel (Sciurus arizonensis) inhabits arid forests in which precipitation is highly seasonal and exceptionally variable; however, no data are available on diet or reproduction. We investigated annual variation in foraging and reproductive habits of Arizona gray squirrels to assess responses to extreme seasonality. We found that Arizona gray squirrels have a diverse diet, with consumption of major food items shifting between years. Reproduction also varies between years. Reproductive output was greater in 2008, with more females successfully reproducing and males remaining in reproductive condition for extended periods. Males shifted timing of reproductive behaviors in response to female receptivity, which tracked food availability. This shift likely reflects variation in food production due to precipitation, because rainfall varied greatly, with most years prior to and during our study recording below-average rainfall. With drought conditions and extreme rainfall events predicted to increase with climate change, understanding the relationship between climatic events, phenology of food production, and impacts on reproduction is critical when attempting to manage and conserve species. [ABSTRACT FROM AUTHOR]

Identifying how density and number-dependent processes regulate populations is important for predicting population response to environmental change. Species that live in groups, such as shoaling fish, can experience both direct density-dependent mortality through resource limitation and inverse number-dependent mortality via increased feeding rates and predator evasion in larger groups. To investigate the role of these processes in a temperate reef fish population, we manipulated the density and group size of the shoaling species Trachinops caudimaculatus on artificial patch reefs at two locations with different predator fields in Port Phillip Bay, Australia. We compared mortality over four weeks to estimates of predator abundance and per capita availability of refuge and food to identify mechanisms for density or number dependence. Mortality was strongly directly density dependent throughout the experiment, regardless of the dominant predator group; however, the limiting resource driving this effect changed over time. In the first two weeks when densities were highest, density-dependent mortality was best explained by refuge competition and the abundance of benthic predators. During the second two weeks, food competition best explained the pattern of mortality. We detected no effect of group size at either location, even where pelagic-predator abundance was high. Overall, direct density effects were much stronger than those of group size, suggesting little survival advantage to shoaling on isolated patch reefs where resource competition is high. This study is the first to observe a temporal shift in density-dependent mechanisms in reef fish, and the first to observe food limitation on short temporal scales. Food competition may therefore be an important regulator of postsettlement reef fish cohorts after the initial intense effects of refuge limitation and predation. [ABSTRACT FROM AUTHOR]

Plant growth can be limited by resource acquisition and defence against consumers, leading to contrasting trade-off possibilities. The competition-defence hypothesis posits a trade-off between competitive ability and defence against enemies (e.g. herbivores and pathogens). The growth-defence hypothesis suggests that strong competitors for nutrients are also defended against enemies, at a cost to growth rate. We tested these hypotheses using observations of 706 plant populations of over 500 species before and following identical fertilisation and fencing treatments at 39 grassland sites worldwide. Strong positive covariance in species responses to both treatments provided support for a growth-defence trade-off: populations that increased with the removal of nutrient limitation (poor competitors) also increased following removal of consumers. This result held globally across 4 years within plant life-history groups and within the majority of individual sites. Thus, a growth-defence trade-off appears to be the norm, and mechanisms maintaining grassland biodiversity may operate within this constraint. [ABSTRACT FROM AUTHOR]

Andromonoecy ( i.e. the occurrence on individual plants of hermaphroditic and male flowers) is a rare sexual system among the angiosperms, regarded by some authors as a transitional stage from hermaphroditism to monoecy. Having discovered the occurrence of andromonoecy in Erophaca baetica (a Mediterranean shrubby legume with two subspecies), a novelty for Old World papilionoid legumes, we investigated the morpho-functional correlates and the geographical distribution of this phenomenon in the species. The relative frequencies of hermaphrodite and male flowers were determined in two field and 111 herbarium populations. Biomass allocation within flowers, pollen production and viability, pollen tube growth, nectar production and the temporal pattern of male flower production were also studied in two nearby southern Spanish populations. Virtually all of the studied populations were andromonoecious. Male flowers tended to appear at apical positions within the inflorescence, and became more abundant by the end of the flowering season. Male flowers were externally similar to hermaphroditic flowers (although with less biomass and smaller parts) and released equivalent amounts of pollen and nectar; however, their pollen germinated significantly better. Erophaca is the first example of an andromonecious Papilionoid in the Old World. Since the main difference among floral morphs in this species is functional ( i.e. pollen germination rate) rather than morphological, andromonoecy is not readily noticeable, and very careful inspection may be required to reveal it. The potential effect of andromonoecy in enhancing outcrossing rate in this species is discussed. [ABSTRACT FROM AUTHOR]

Two interacting forces influence all populations: the Malthusian dynamic of exponential growth until resource limits are reached, and the Darwinian dynamic of innovation and adaptation to circumvent these limits through biological and/or cultural evolution. The specific manifestations of these forces in modern human society provide an important context for determining how humans can establish a sustainable relationship with the finite Earth. [ABSTRACT FROM AUTHOR]

The limits on annual seed production have long been characterized as restriction by either pollination success or resource provision to seed development. This expected dichotomy between pollen and resource limitation is based on the assumption that reproductive resources are fixed, which is reasonable for semelparous species. In contrast, iteroparity can ease the constraints on reproductive output per breeding season, if resources can be either mobilized from past storage or borrowed against future performance. For perennial plants, these options allow enhanced reproductive investment in response to unusually good pollination, so that annual seed production may not be pollen or resource limited. We assessed demand-governed reproductive investment by manipulating both resoutce supply capacity (partial defoliation) and resource demand (pollination quality: fully self-pollination, fully cross-pollination, or combinations of partial self- and cross-pollination within the inflorescence) for a forest herb, Stenanthium occidentale, which is subject to strong pre-dispersal inbreeding depression. Insensitivity to partial defoliation indicated that reproductive output was not source regulated. Instead, demand by developing seeds governs resource distribution, as demonstrated by elevated photosynthate translocation to fruits on fully cross-pollinated plants and the ability of completely defoliated plants to produce seeds. Such contingent resource allocation eliminates a simple dichotomy between pollen receipt and resource availability as limits on annual seed production. Instead, such flexible reproductive investment allows iteroparous perennials to participate maximally in current reproduction (as determined by ovule production) following superior pollination, or to conserve resources for future reproduction following poor pollination. [ABSTRACT FROM AUTHOR]

The ultimate goal of this multi-article series is to develop a methodology to generate continuous fields of tree height and biomass. The first paper demonstrated the need for Allometric Scaling and Resource Limitation (ASRL) model optimization and its ability to generate spatially continuous fields of tree heights over the continental USA at coarse (1 km) spatial resolution. The objective of this second paper is to provide an assessment of that approach at site scale, specifically at 12 FLUXNET sites where more accurate data are available. Estimates of tree heights from the Geoscience Laser Altimeter System (GLAS) waveform data are used for model optimization. Amongst the five possible GLAS metrics that are representative of tree heights, the best metric is selected based on how closely the metric resembles field-measured and Laser Vegetation Imaging Sensor tree heights. In the optimization process, three parameters of the ASRL model (area of single leaf, α; exponent for canopy radius, η; and root absorption efficiency, γ) are simultaneously adjusted to minimize the difference between model predictions and observations at the study sites (distances to valid GLAS footprints ≤ 10 km). Performance of the optimized ASRL model was evaluated through comparisons to the best GLAS metric of tree height using a two-fold cross validation approach (R2 = 0.85; RMSE = 1.81 m) and a bootstrapping approach (R2 = 0.66; RMSE = 2.60 m). The optimized model satisfactorily performed at the site scale, thus corroborating results presented in part one of this series. Future investigations will focus on generalizing these results and extending the model formulation using similar allometric concepts for the estimation of woody biomass. [ABSTRACT FROM AUTHOR]

Understanding the process by which limiting resources are incorporated into populations is a major goal of ecology. While many studies have examined this dynamic process using essential resources like homes, few of these studies have involved homes that can be transported by their occupants. This study introduced over a thousand transportable homes into a population of terrestrial hermit crabs Coenobita compressus, animals that carry their homes with them wherever they travel. These new homes were tracked between years to test key predictions about the temporal dynamics the homes would generate, and the spatial and structural changes the homes would undergo as they were used by the population. When moving into new homes, crabs dropped off their old homes directly at the exchange site, and the number of such traded-in homes peaked rapidly in time. Traded-in homes were under half the diameter of new homes, a difference apparently magnified by social formations involving vacancy chains. After crabs moved into new homes, they carried the homes away from the exchange site. The following year, these homes were displaced a distance four orders of magnitude times their diameter, thus penetrating extensively through the population. Between years, crabs also remodeled the internal architecture of the homes, creating homes that were more spacious and less of a burden to carry. These results suggest that transportable homes generate novel ecological dynamics along temporal, spatial and structural dimensions, which are a direct consequence of their transportability. [ABSTRACT FROM AUTHOR]

The relationships of local population density ( N) with body size ( M) and distribution ( D) have been extensively studied because they reveal how ecological and historical factors structure species communities; however, a unifying model explaining their joint behaviour, has not been developed. Here, I propose a theory that explores these relationships hierarchically and predicts that: (1) at a metacommunity level, niche breadth, population density and regional distribution are all related and size-dependent and (2) at a community level, the exponents b and d of the relationships N ~ M b and N ~ D d are functions ( f) of the environment and, consequently, species richness ( S), allowing the following reformulation of the power laws: N ~ M f(S) and N ~ D f(S). Using this framework and continental data on stream environment, diatoms, invertebrates and fish, I address the following fundamental, but unresolved ecological questions: how do species partition their resources across environments, is energetic equivalence among them possible, are generalists more common than specialists, why are locally abundant species also regionally prevalent, and, do microbes have different biogeography than macroorganisms? The discovery that community scaling behaviour is environmentally constrained calls for better integration of macroecology and environmental science. [ABSTRACT FROM AUTHOR]

Abstract: Cavity shortage limits secondary cavity-nesting birds (SCN) assemblages in intensively-managed forests with few cavities, but whether cavity availability limits SCN in cavity-rich forests remains unclear. To address this issue, we used a replicated before-after-control-impact design in which the availability of cavities was experimentally reduced and increased in cavity-rich Quercus pyrenaica forests. Cavity-blocking and nest-box addition led to reduction by 66% and increase by 185%, respectively, of nest densities of blue (Cyanistes caeruleus) and great (Parus major) tits. Analysis of cavity characteristics suggests that tits occupied less suitable cavities in blocking plots compared to control and nest-box addition plots after treatments, further indicating that the availability of suitable nest-sites may limit tit populations. No effect of cavity manipulation was found for short-toed treecreepers (Certhia brachydactyla) and Eurasian nuthatches (Sitta europaea), which defend larger territories than tits and whose numbers may be more influenced by territoriality than by nest-sites. Alternatively, high plasticity in nest-site use of treecreepers may enable them to cope with reductions in cavity availability and increased interspecific competition. Spotless starlings (Sturnus unicolor) were little affected by cavity manipulation. Often foraging on pastures, starlings may be more limited through reduced foraging opportunities in this forested landscape than by nest-sites. In addition, starlings may exclude other species from their preferred cavities to cope with reductions in numbers of suitable cavities. Community responses to the variation in cavity abundance in cavity-rich Pyrenean oak forests may therefore vary considerably among species, depending on their plasticity in nest-site use, behavioral dominance, foraging conditions or social structure. Thus, management actions aimed to increase cavity abundance and suitability for SCN communities in cavity-rich forests should consider inter-specific interactions and species-specific characteristics of the targeted species. [Copyright &y& Elsevier]

Background and aims: Nutrients are important determinants of community assembly, yet the roles they play in structuring plant communities are still poorly understood. One inferential approach to understanding how environmental factors structure plant communities is examining the distribution of key functional traits among species of a community-a community traitscape. Methods: To better understand how nitrogen (N) and water availability structure grasslands, we measured N concentrations and isotope ratios for 366 herbaceous species in a mesic N-limited temperate grassland, Konza Prairie. We also compared foliar N concentrations and N isotopes between Konza species and a global dataset. Results: Species that had either high foliar N concentrations or high δN were not necessarily more or less abundant on the landscape nor more or less likely to be found in uplands, grazed areas, or burned areas. Apparently there are unique hot spots of high N availability at Konza and the typical non-Fabaceae Konza species occupies sites with greater N availability than found globally. Conclusions: Although nascent, the Konza traitscapes suggest that plant diversity in nutrient-limited communities might be strongly dependent on high-nutrient availability sites that enable high-fertility species to persist in a matrix of low nutrient availability. [ABSTRACT FROM AUTHOR]

Ecology Letters (2012) 15: 748-758 Abstract Forest and savanna biomes dominate the tropics, yet factors controlling their distribution remain poorly understood. Climate is clearly important, but extensive savannas in some high rainfall areas suggest a decoupling of climate and vegetation. In some situations edaphic factors are important, with forest often associated with high nutrient availability. Fire also plays a key role in limiting forest, with fire exclusion often causing a switch from savanna to forest. These observations can be captured by a broad conceptual model with two components: (1) forest and savanna are alternative stable states, maintained by tree cover-fire feedbacks, (2) the interaction between tree growth rates and fire frequency limits forest development; any factor that increases growth (e.g. elevated availability of water, nutrients, CO2), or decreases fire frequency, will favour canopy closure. This model is consistent with the range of environmental variables correlated with forest distribution, and with the current trend of forest expansion, likely driven by increasing CO2 concentrations. Resolving the drivers of forest and savanna distribution has moved beyond simple correlative studies that are unlikely to establish ultimate causation. Experiments using Dynamic Global Vegetation Models, parameterised with measurements from each continent, provide an important tool for understanding the controls of these systems. [ABSTRACT FROM AUTHOR]

Inbreeding depression can reduce the performance of offspring produced by mating between relatives, with consequences for population dynamics and sexual-system evolution. In flowering plants, inbreeding depression commonly acts most intensely during seed development. This predispersal component is typically estimated by comparing seed production following exclusive self- and cross-pollination, but such estimates are unbiased only if seed production is limited by ovule availability, rather than by pollen receipt or seed-development resources. To overcome this problem, we propose experimental and statistical methods based on a model of ovule fertilization and seed development that accounts for differential fertilization by self- and cross-pollen, limited ovule viability or receptivity, differential survival of self- and cross-zygotes and limited resource availability. Simulations illustrate that the proposed methods eliminate bias in estimated predispersal inbreeding depression caused by pollen limitation and can improve estimates under resource limitation. Application of these methods to two orchid species further demonstrates their utility in identifying and estimating diverse influences on reproductive performance under typical conditions. Although our theoretical results raise questions about the reported intensity of predispersal inbreeding depression, our proposed methods guard against bias while also providing insight into plant reproduction. [ABSTRACT FROM AUTHOR]

Tropical forest productivity is widely assumed to be limited by soil phosphorus (P), but biogeochemical processes that deplete P also could deplete base cations, suggesting multiple resource limitation. Limitation by several resources could arise from species and functional diversity and from variation among groups in resource requirements, including ecophysiological strategies that minimize P limitation. We hypothesized that tree growth is positively related to soil base cation and P availability and negatively related to local competition; Fabaceae growth is weakly correlated with soil resources if fixed N is used indirectly to acquire other resources; growth of species with low wood density is more strongly related to soil resource availability than that of species with high wood density. Diameter growth and soil resource availability were measured in five mapped stands situated across natural soil resource gradients in lowland wet tropical forest (La Selva Biological Station, Costa Rica). Soil resource availability, and associated uncertainty, was estimated for each tree using a Bayesian multivariate spatial regression model, with individual tree growth being a function of diameter, local neighborhood, and soil resources. Separately, site-level mean tree growth and resource availability were modeled using linear regression. Individual diameter growth and site mean basal area increment correlated with soil base cations and P, but rarely with N; individual growth correlated negatively with neighborhood index for only three species. Growth of Fabaceae was unrelated to soil resources at both individual and site levels. When species were categorized by wood density, growth was related to soil P or base cation availability, with the strongest correlation between the lowest-density species and soil P. Several resources may limit tropical forest productivity, because tree growth was similarly correlated with soil P and base cations, but functional groups responded differently. Negligible growth relationships with soil resources in Fabaceae suggest that N fixation may alleviate mineral nutrient limitations. Correlations of soil P with growth of species of low wood density and base cations with species of higher density suggests variation in resource demands among functional groups. Thus, tropical tree growth may be limited by base cations and/or P, with degree and type of resource limitation dependent on functional or taxonomic group. [ABSTRACT FROM AUTHOR]

We investigated the role of resource limitation, ovary reserve, and selective abortion in controlling flower and fruit set in the Mediterranean leguminous shrub Anagyris foetida. The removal of bracts, but not that of leaves, reduced the initiation of fruit with respect to controls. The removal of a large proportion (2/3 of the total) of preanthesic inflorescences increased the reproductive capacity of individuals via two different strategies: (1) maintaining the number of fruit-bearing inflorescences, but increasing the number of fruits per inflorescence and seeds per fruit; and (2) increasing the number of fruit-bearing inflorescences, while maintaining fruits/inflorescence and seeds/fruit ratios unchanged. At the level of the inflorescence, most of the ripe fruits were located on the basalmost whorls of the raceme. Within the legume, fertilization was independent of the position of ovules, although the more basal presented lower rates of fertilization than the more central-stylar. The same was observed for the probability of a fertilized ovule to develop into a mature seed. [ABSTRACT FROM AUTHOR]

Abstract: Flowers of many plant species are visited by both birds and insects, making it necessary to establish their relative contributions to seed set. In Protea, available evidence points to an overwhelming preponderance of bird-pollination systems in the genus, but the scented flowers of several dwarf grassland “sugarbush” species suggest that some Protea species may be adapted for insect pollination. In this study, we used both selective exclusion of vertebrates and complete exclusion of all visitors to investigate whether the insects that visit the scented flowerheads of three Protea species (Protea dracomontana, Protea simplex and Protea welwitschii) in KwaZulu-Natal, South Africa contribute to seed production. We also performed supplemental hand pollinations to test for pollen limitation. Seed set was generally higher in inflorescences subjected to vertebrate exclusion than in those from which all visitors were excluded, suggesting that fertile cross-pollen was deposited by insects, but these differences were slight because of high levels of self-fertilization in the study species. Pollen deposition and pollen tube growth were similar for vertebrate-excluded and open-pollinated inflorescences. Supplemental hand-pollination treatments revealed that seed set in P. simplex and P. welwitschii was not pollen-limited. Overall seed set was low, typical of the family Proteaceae, and infructescences were highly predated by lepidopteran larvae. We conclude that insects are likely to contribute to seed set of the study species, but further studies using molecular markers are required to establish the actual level of insect-mediated outcrossing. [Copyright &y& Elsevier]

Although spiders are a diverse and ecologically important group of predators across the sub-Antarctic islands, relatively little is known about their biology. Here we provide data on the abundance, body size variation and sex ratio of an indigenous spider, Myro kerguelenensis, across an altitudinal gradient on Marion Island. In so doing we test explicitly the hypotheses that density will decline with declining resource availability at higher elevations, and that a converse Bergmann body size cline will be found in this species. Density of M. kerguelenensis decreased with altitude and ranged from a mean density of 5.3 (SD 3.42) individuals per m2 at 50 m a.s.l. to a mean density of 0.83 (SD 1.15) individuals per m2 at 600 m a.s.l. Mean female sternum width was 1.39 mm (SD 0.44) and mean male sternum width was 1.40 mm (SD 0.22). No evidence for Bergmann or converse Bergmann clines was found. At increasing altitudes, sex ratios became increasingly female-biased with populations at 600 m a.s.l. comprising 0.87 (SD 0.28) females, on a proportional basis, possibly as a result of resource limitation and an increase in the prevalence of sexual cannibalism. The food web implications of this study are highlighted. [ABSTRACT FROM AUTHOR]

We investigated the role of resource limitation, ovary reserve, and selective abortion in controlling flower and fruit set in the Mediterranean leguminous shrub Anagyris foetida. The removal of bracts, but not that of leaves, reduced the initiation of fruit with respect to controls. The removal of a large proportion (2/3 of the total) of preanthesic inflorescences increased the reproductive capacity of individuals via two different strategies: (1) maintaining the number of fruit-bearing inflorescences, but increasing the number of fruits per inflorescence and seeds per fruit; and (2) increasing the number of fruit-bearing inflorescences, while maintaining fruits/inflorescence and seeds/fruit ratios unchanged. At the level of the inflorescence, most of the ripe fruits were located on the basalmost whorls of the raceme. Within the legume, fertilization was independent of the position of ovules, although the more basal presented lower rates of fertilization than the more central-stylar. The same was observed for the probability of a fertilized ovule to develop into a mature seed. [ABSTRACT FROM AUTHOR]

Food limitation is one of the most important extrinsic factors influencing population dynamics in aquatic ecosystems, but the spatial patterns of resource limitation and their influence on zooplankton species have not been investigated. We tested the hypothesis that the occurrence and intensity of food limitation may vary both spatially and temporally, and that the irregular population dynamics of the rotifers Brachionus group plicatilis and Hexarthra jenkinae in a saline, warm-monomictic, oligotrophic lake (Alchichica, Central Mexico) can be attributed to resource limitation. We estimated plankton abundance and composition and performed 19 laboratory experiments to assess the intensity of food limitation (Δr) at three selected depths in the water column. Most of the phytoplankton biomass consisted of algae inedible to rotifers, and good-quality food (phytoplankton ≤20 µm + small heterotrophic flagellates) was frequently below the threshold food concentration for Brachionus species. The vertical distribution and abundance of rotifers were correlated with the availability of food resources. Food limitation was observed during mixing and late stratification; however, the intensity of limitation was rather similar throughout the water column owing to the overall scarcity of resources in the lake. Hexarthra seldom appeared. We conclude that the irregular pattern of rotifer abundance we observed is a consequence of the interplay between the harsh conditions of scarce food availability, resulting in intense resource competition and opportunities for rapid exploitation of opportunities when food outbursts occur. [ABSTRACT FROM AUTHOR]

Background and Aims Plants are sessile organisms that face selection by both herbivores and pollinators. Herbivores and pollinators may select on the same traits and/or mediate each others' effects. Erysimum capitatum (Brassicaceae) is a widespread and variable plant species with generalized pollination that is attacked by a number of herbivores. The following questions were addressed. (a) Are pollinators and herbivores attracted by similar plant traits? (b) Does herbivory affect pollinator preferences? (c) Do pollinators and/or herbivores affect fitness and select on plant traits? (d) Do plant compensatory responses affect the outcome of interactions among plants, pollinators and herbivores? (e) Do interactions among E. capitatum and its pollinators and herbivores differ among sites and years? Methods In 2005 and 2006, observational and experimental studies were combined in four populations at different elevations to examine selection by pollinators and herbivores on floral traits of E. capitatum. Key Results Pollinator and herbivore assemblages varied spatially and temporally, as did their effects on plant fitness and selection. Both pollinators and herbivores preferred plants with more flowers, and herbivory sometimes reduced pollinator visitation. Pollinators did not select on plant traits in any year or population and E. capitatum was not pollen limited; however, supplemental pollen resulted in altered plant resource allocation. Herbivores reduced fitness and selected for plant traits in some populations, and these effects were mediated by plant compensatory responses. Conclusions Individuals of Erysimum capitatum are visited by diverse groups of pollinators and herbivores that shift in abundance and importance in time and space. Compensatory reproductive mechanisms mediate interactions with both pollinators and herbivores and may allow E. capitatum to succeed in this complex selective environment. [ABSTRACT FROM PUBLISHER]

Summary 1. Surface ecosystems provide the primary source of organic matter to many cave communities. Variation in the strength of connectivity to the surface suggests that some caves may be more resource-limited than others. To test this, we examined diet, prey availability and production of an obligate cave salamander Gyrinophilus palleucus (Plethodontidae), a top predator, in two south-eastern U.S.A. caves with different levels of organic matter (Tony Sinks cave, 165 g AFDM m−2; Bluff River cave, 62 g AFDM m−2). 2. We quantified density, biomass, growth rate, production and diet of G. palleucus monthly for 21 months. Diet composition, differences in prey communities and seasonal patterns in prey consumption were also analysed. 3. Salamander density, biomass and secondary production were significantly greater in the high organic matter cave (0.10 m−2, 0.18 g AFDM m−2, 0.12 g AFDM m−2 year−1) than in the low organic matter cave (0.03 m−2, 0.03 g AFDM m−2, 0.01 g AFDM m−2 year−1). Although growth rates were not statistically different between the two cave salamander populations, low recaptures probably influenced this result. 4. Isopoda prey were the major contributor to salamander production in the high organic matter cave (69%). In the low organic matter cave, production was provided by isopods (41%) and oligochaetes (20%). The lower number of prey taxa contributing to salamander production in the high organic matter cave suggests the ability to forage more selectively. 5. The differences in foraging strategy, density, biomass and secondary production were probably related to differences in the strength of surface connectivity, which controls organic matter supply. Links between basal resource level and top predator performance show the importance of bottom-up limitation in the food webs of caves and other detritus-based ecosystems. [ABSTRACT FROM AUTHOR]

The Gouldian Finch (Erythrura gouldiae) has experienced significant decline in population and the extent of its range over the past 40 years, which has generally been attributed to the availability of suitable foraging habitat. Less research, however, has investigated the suitability or availability of breeding habitat of the species. Gouldian Finches are obligate cavity nesters, and a recent study has shown that they select nest-sites non-randomly based on structural characteristics of the cavity. Here we investigated the relative effects of different environmental factors on the spatial distribution of Gouldian Finch nests at two different scales. At the broader, landscape scale (over ~60 km²), the strongest predictor of nesting density at a site was the abundance of suitable nest-sites. At the finer scale (~1 km²), no single factor explained the variation in location of nest-sites. Gouldian Finches require areas of habitat characterised by high densities of suitable nest-sites (tree-cavities). Within these patches, individuals are potentially selecting nest-sites based on the morphometry of cavities rather than landscape features such as topography, vegetation or proximity to water. Our findings should be integrated with studies of feeding and habitat requirements in the non-breeding season, with the aim of constructing holistic and predictive habitat-suitability models for this endangered species. [ABSTRACT FROM AUTHOR]

Abstract: Evidence supporting water limitation in arid-semiarid ecosystems includes strong correlations between aboveground net primary production (ANPP) and annual precipitation as well as results from experimental water additions. Similarly, there is evidence of N limitation on ANPP in low precipitation ecosystems, but is this a widespread phenomenon? Are all arid-semiarid ecosystems equally limited by nitrogen? Is the response of N fertilization modulated by water availability? We conducted a meta-analysis of ANPP responses to N fertilization across arid to subhumid ecosystems to quantify N limitation, using the effect-size index R which is the ratio of ANPP in fertilized to control plots. Nitrogen addition increased ANPP across all studies by an average of 50%, and nitrogen effects increased significantly (P = 0.03) along the 50–650 mm yr−1 precipitation gradient. The response ratio decreased with mean annual temperature in arid and semiarid ecosystems but was insensitive in subhumid systems. Sown pastures showed significant (P = 0.007) higher responses than natural ecosystems. Neither plant-life form nor chemical form of the applied fertilizer showed significant effects on the primary production response to N addition. Our results showed that nitrogen limitation is a widespread phenomenon in low-precipitation ecosystems and that its importance increases with annual precipitation from arid to subhumid regions. Both water and N availability limit primary production, probably at different times during the year; with frequency of N limitation increasing and frequency of water limitation decreasing as annual precipitation increases. Expected increase N deposition, which could be significant even in arid ecosystems, would increase aboveground net primary production in water-limited ecosystems that account for 40% of the terrestrial surface. [Copyright &y& Elsevier]

Changes in climate and land use can impact natural systems across all levels of ecological organization. Most documented and anticipated effects consider species' properties, including phenologies, geographic distributions, and abundances. Responses of higher-level aggregate community or ecosystem properties have not been considered as they are assumed to be relatively stable due to compensatory dynamics and diversity-stability relationships. However, this assumption may not be as fundamental as previously thought. Here we assess stability in the aggregate properties of total abundance, biomass, and energy consumption for small-mammal communities in the Great Basin, using paired historical and modern survey data spanning nearly a century of environmental change. Results show marked declines in each aggregate property independent of spatial scale, elevation, or habitat type, and a reallocation of available biomass and energy favoring diet and habitat generalists. Because aggregate properties directly reflect resource availability, our findings indicate a regionwide decline in resources of 50% over the past century, which may signal a resource crisis. This work illustrates the power of using aggregate properties as indicators of ecological conditions and environmental change at broad spatial and temporal scales. [ABSTRACT FROM AUTHOR]

Ungulate populations in African conservation areas (CAs) are in widespread decline, which can largely be attributed to a lack of functionality of the area encompassed by the CAs themselves. We present evidence from a wide range of African CAs showing that they do not encompass both the functional wet- and dry-season resources that ungulates traditionally migrated between. Before human populations and economic development had grown to levels where they interfered with migrations outside the CAs, ungulates were able to make use of their traditional seasonal resources but this is becoming increasingly difficult and we are now seeing the effects of this restriction of movement on ungulate population numbers. New innovative strategies are required for the conservation of African wildlife. An urgent Africa-wide survey is needed to establish past and present functional resources in and around CAs and to prioritize conservation regions that are most functional. In addition, innovative attempts need to be made to reconsolidate functional seasonal resources within revised expanded protected areas. [ABSTRACT FROM AUTHOR]

In some systems, grasshoppers appear to be food limited in most years, whereas in other systems top down forces, for example, predators, are more often implicated in population regulation. Sustainable strategies to manage grasshopper populations through habitat management require knowledge of the forces that regulate grasshopper populations. This experiment was undertaken to determine whether populations of Melanoplus borealis (Fieber), a common pest species in Alaska, are food-limited in Alaska, Cages were set up in a fallow field near Delta Junction, AK, in 3 yr (2007-2009), In 2007 and 2008, fertilizer was added to half the plots to increase primary production, and, in all years, cages within each plot were stocked with 0, 5, 9, or 13 fourth-instar M. borealis (equivalent to 0, 20, 36, or 52 grasshoppers/m²), Grasshoppers in each cage were counted weekly. Near the end of the growing season, surviving female grasshoppers (≈40% of the original number) were collected. Femur length was taken as a measure of adult size, and functional overrules were counted as a measure of current fecundity. If the grasshoppers were food limited, we expected to see significant effects of either density or fertilizer on grasshopper survival, size, or fecundity. The fertilizer treatment greatly increased primary production in both years. Neither fertilizer treatment nor grasshopper density had consistent effects on survival, size, or potential fecundity, leading us to conclude that food is seldom limiting to populations in the interior of Alaska at densities <50 m-2. [ABSTRACT FROM AUTHOR]