Find research datasets worth reusing

Data from: Field manipulations of resources mediate the transition from intraspecific competition to facilitation

1. Population density affects individual performance, though its effects are often mixed. For sessile species, increases in population density typically reduce performance. Still, cases of positive density dependence do occur in these systems and demand explanation. The stress gradient hypothesis (SGH) predicts that under stressful conditions, positive effects of facilitation may outweigh the negative effects of competition. 2. While some elements of the SGH are well studied, its potential to explain intraspecific facilitation has received little attention. Further, there have been questions regarding whether the SGH holds if the stressor is a resource. Most studies of interactions between the environment and intraspecific facilitation have relied on natural environmental gradients; manipulative studies are much rarer. 3. To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata. 4. We found negative effects of density on colony performance in low resource environments, but mainly positive density-dependence in high resource environments. By adding resources, competition effects were reduced and the positive effects of facilitation were revealed. 5. Our results suggest that resource availability mediates the relative strength of competition and facilitation in our system. We also suggest that intraspecific facilitation is more common than may be appreciated and that environmental variation may act as mediators to the balance between negative and positive density-dependence.

opencc-zeroDec 2019View details →

Deer movement and resource selection during Hurricane Irma: implications for extreme climatic events and wildlife

Extreme climatic events (ECEs) are increasing in frequency and intensity and this necessitates understanding their influence on organisms. Animal behavior may mitigate the effects of ECEs, but field studies are rare because ECEs are infrequent and unpredictable. Hurricane Irma made landfall in southwestern Florida where we were monitoring white-tailed deer (Odocoileus virginianus seminolus) with GPS collars. We report on an opportunistic case study of behavioral responses exhibited by a large mammal during an ECE, mitigation strategies for reducing the severity of the ECE effects, and the demographic effect of the ECE based on known-fate of individual animals. Deer altered resource selection by selecting higher elevation pine and hardwood forests and avoiding marshes. Most deer left their home ranges during Hurricane Irma, and the probability of leaving was inversely related to home range area. Movement rates increased the day of the storm, and no mortality was attributed to Hurricane Irma. We suggest deer mobility and refuge habitat allowed deer to behaviorally mitigate the negative effects of the storm, and ultimately, aid in survival. Our work contributes to the small but growing body of literature linking behavioral responses exhibited during ECEs to survival, which cumulatively will provide insight for predictions of a species resilience to ECEs and improve our understanding of how behavioral traits offset the negative impacts of global climate change.

opencc-zeroDec 2017View details →

Data from: Consumer-resource interactions along urbanization gradients drive natural selection

Urbanization is an important component of global change. Urbanization affects species interactions, but the evolutionary implications are rarely studied. We investigate the evolutionary consequences of a common pattern: the loss of high trophic-level species in urban areas. Using a gall-forming fly, Eurosta solidaginis, and its natural enemies that select for opposite gall sizes, we test for patterns of enemy loss, selection, and local adaptation along five urbanization gradients. Eurosta declined in urban areas, as did predation by birds, which preferentially consume gallmakers that induce large galls. These declines were linked to changes in habitat availability, namely reduced forest cover in urban areas. Conversely, a parasitoid which attacks gallmakers that induce small galls was unaffected by urbanization. Changes in patterns of attack by birds and parasitoids resulted in stronger directional selection, but loss of stabilizing selection in urban areas, a pattern which we suggest may be general. Despite divergent selective regimes, gall size did not very systematically with urbanization, suggesting but not conclusively demonstrating that environmental differences, gene flow, or drift, may have prevented the adaptive divergence of phenotypes. We argue that the evolutionary effects of urbanization will have predictable consequences for patterns of species interactions and natural selection.

Data from: Resource availability and roosting ecology shape reproductive phenology of rain forest insectivorous bats

Bats in temperate and subtropical regions typically synchronize birth of a single young with peaks in resource availability driven by local climate patterns. In tropical rain forest, insects are available throughout the year, potentially allowing departures from seasonal monoestry. However, reproductive energy budgets may be constrained by the cost of commuting to foraging grounds from distant roosts. To test these hypotheses, we simultaneously tracked female reproductive activity of 11 insectivorous bat species, insect biomass, and local weather variables for 20 months in a Malaysian rain forest. Five species roost in forest structures and hence have low commuting costs, whereas six species depend on caves, which are limited in the landscape, and are presumed to incur higher commuting costs to foraging sites. Monthly insect biomass was positively correlated with monthly rainfall, and there was a significant relationship between insect biomass and lactation in cave-roosting but not forest-roosting species. Cave-roosting species were seasonally monoestrus, with parturition confined to a two-month period, whereas in forest-roosting species, pregnancy and lactation were recorded throughout the year. Our results suggest that the energetic costs of commuting from roosts to foraging grounds shape annual reproductive patterns in tropical rain forest insectivorous bats. Ongoing changes in forest landscapes are likely to increase these costs for cave-roosting bats, further restricting reproductive opportunities. Climate change is projected to influence the timing of rainfall events in many tropical habitats, which may disrupt relationships between rainfall, insect biomass, and bat reproductive timing, further compromising reproductive success.

opencc-zeroApr 2014View details →

Data from: Pulsing hydrology determines top-down control of basal resources in a tropical river-floodplain ecosystem

Variable hydrology of rivers strongly affects biophysical factors that influence primary production and population densities, thereby affecting the relative influence of bottom-up and top-down processes in trophic networks. Many tropical floodplain rivers have sustained seasonal flood pulses driven by precipitation patterns of the Intertropical Convergence Zone. These changes in flow alter concentrations of dissolved nutrients, aquatic primary productivity, and per-unit-area densities of aquatic organisms. Therefore, one would predict that the strength of top-down effects of animals on basal resources should shift as the annual flood pulse progresses. We conducted a series of field experiments in a Neotropical lowland river to test for effects of hydrologic phase, habitat (in-channel vs. floodplain aquatic habitat), and benthic feeding fish and meiofauna on particulate organic matter, chlorophyll, and benthic microalgae. Net ecosystem productivity of this oligotrophic river is higher during the low phase of the annual flood cycle, which is also when resident fishes are at highest densities and there is a seasonal influx of migratory benthic feeding fish. We therefore hypothesized that top-down effects of benthic-feeding fish would fluctuate temporally, with strongest effects during low water levels. We found that fish controlled the abundance of particulate organic matter and algae on solid substrates, but not on sand, during falling- and low-water phases within both channel and floodplain habitats. Except for diatom assemblages, which responded to fish exclusion, the taxonomic structure of algal and meiofauna assemblages was not significantly influenced by fish exclusion treatments, but varied in relation to habitat type and hydrologic phase. Meiofauna densities were highest during the low-water period; experimental exclusion of meiofauna during this period had a significant effect on accumulation of particulate organic matter in sand. By controlling abundance of important basal resources, fishes and meiofauna have large potential to influence other components of this tropical ecosystem. Our findings emphasize the predictable, gradual, changes in consumer-resource interactions associated with the seasonal flood pulse in tropical river systems.

Data from: Seed set variation in wild Clarkia populations: teasing apart the effects of seasonal resource depletion, pollen quality, and pollen quantity

In habitats where resource availability declines during the growing season, selection may favor early-flowering individuals. Under such ephemerally favorable conditions, late-blooming species (and individuals) may be particularly vulnerable to resource limitation of seed production. In California, a region prone to seasonal drought, members of the annual genus Clarkia are among the last to flower in the spring. We compared pollen limitation (PL) of seed set and outcrossing rates between early- and late-flowering individuals in two mixed-mating Clarkia taxa to detect whether flowering time is associated with changes in seed set due to resource depletion, PL, or increased selfing. In 2008–2010, we hand-pollinated one flower on a total of 1855 individual plants either Early (near the onset of flowering) or Late (near the end of flowering) in the flowering season and compared seed set to adjacent, open-pollinated flowers on the same stem. To assess the contribution of pollen quality to reproduction, we first (2008) used allozymes to estimate outcrossing rates of seeds produced by Early and Late open-pollinated flowers. Second (2009), we conducted an anther-removal experiment to estimate self-pollen deposition. Seed set in Clarkia unguiculata was not pollen-limited. Clarkia xantiana ssp. xantiana was pollen-limited in 2008 and 2010, but not 2009. PL did not differ between Early and Late treatments. In both taxa, seed set of Early flowers was greater than Late flowers, but not due to PL in the latter. Reproduction was generally pollinator-dependent. Most pollen deposition was xenogamous, and outcrossing rates were >0.7 – and similar between Early and Late periods. These results suggest that pollen receipt and pollen quality remain seasonally consistent. By contrast, the resources necessary to provision seeds decline, reducing the fitness benefits associated with resource allocation to ovules.

opencc-zeroDec 2013View details →

Data from: Environmental filtering explains variation in plant diversity along resource gradients

The mechanisms that shape plant diversity along resource gradients remain unresolved because competing theories have been evaluated in isolation. By testing multiple theories simultaneously across a >2-million-year dune chronosequence in an Australian biodiversity hotspot, we show that variation in plant diversity is not explained by local resource heterogeneity, resource partitioning, nutrient stoichiometry, or soil fertility along this strong resource gradient. Rather, our results suggest that diversity is determined by environmental filtering from the regional flora, driven by soil acidification during long-term pedogenesis. This finding challenges the prevailing view that resource competition controls local plant diversity along resource gradients, and instead reflects processes shaping species pools over evolutionary time scales.

Data from: From resource to female defence: the impact of roosting ecology on a bat's mating strategy

With their extraordinary species richness and diversity in ecological traits and social systems, bats are a promising taxon for testing socio-ecological hypotheses in order to get new insights into the evolution of animal social systems. Regarding its roosting habits, proboscis bats form an extreme by occupying sites which are usually completely exposed to daylight (e.g. tree trunks, vines or rocks). This is accompanied by morphological and behavioural adaptations to remain cryptic in exposed day roosts. With long-term behavioural observations and genetic parentage analyses of individually marked proboscis bats, we assessed its social dispersion and male mating strategy during day and night. Our results reveal nocturnal male territoriality—a strategy which most closely resembles a resource-defence polygyny that is frequent also in other tropical bats. Its contrasting clumped social dispersion during the day is likely to be the result of strong selection for crypsis in exposed roosts and is accompanied by direct female defence in addition to male territoriality. To the best of our knowledge, such contrasting male mating strategies within a single day–night cycle have not been described in a vertebrate species so far and illustrate a possible evolutionary trajectory from resource-defence to female-defence strategy by small ecologically driven evolutionary steps.

Data from: Resource- and pollinator-mediated selection on floral traits

Female reproductive success is predicted to be simultaneously limited by the availability of pollen and resources. Selection on floral traits results from both factors, but their relative importance and interaction is poorly understood. We increased nutrient and pollen availability of the orchid Dactylorhiza lapponica in a factorial experiment to quantify resource- and pollinator-mediated selection on floral traits. Hand-pollination increased female fitness (number of fruits × mean fruit mass) by 74% in both nutrient treatments, whereas nutrient addition did not significantly affect female fitness. There was selection for more flowers and longer spurs, and selection on spur length was significantly pollinator-mediated and of similar strength across nutrient treatments (Δβpoll = 0·54 and Δβpoll_NPK = 0·59). There was no statistically significant resource-mediated selection. Nutrient addition increased flower size the following year, but did not affect flower or fruit production, or selection on any trait. The results demonstrate that D. lapponica does not increase flower production in response to nutrient addition, that the increase in female fitness in response to hand-pollination is not resource limited, and suggest that natural resource variation does not influence selection on floral traits. The study illustrates that crossed manipulations of pollen and resources can clarify their relative importance for selection on floral traits.

opencc-zeroDec 2012View details →

Data from: Responses of social and solitary bees to pulsed floral resources

Pulsed food resources lead to mismatches between distribution of consumers and resources in space and time. Many studies have investigated how pollinators and floral resources covary in space, but few have looked at their covariance among years. I studied responses of two bee taxa, Bombus (a social genus) and Anthophora (a solitary genus), to variation in flowering by Astragalus scaphoides, a perennial herb that flowers in alternate years. First, I quantified the rate at which individual plants were visited by bees. Anthophora showed evidence of a demographic response to resource pulses—that is, more individuals were seen in the year after a high-flowering year—whereas Bombus did not. Second, I quantified pollinator behavior by following individual bees and recording the proportion of visits to A. scaphoides within single foraging bouts. The proportion of visits to A. scaphoides by both taxa increased with A. scaphoides's flowering density. Higher specialization in high-flowering years likely makes both taxa better pollinators in high-flowering years. If these taxa differ in effectiveness as pollinators, then these responses translate into variation in pollination services in space and time, specifically, more activity by Bombus in high-flowering years and more by Anthophora in years following high-flowering years. They also emphasize that pollinator activity depends in part on past—as well as current—floral resources.

Data from: Linking songbird nest predation to seedling density: sugar maple masting as a resource pulse in a forest food web

The ecological literature presents considerable evidence for top-down forcing on the maintenance of species diversity. Yet, in temperate forests, bottom-up forces often exert a strong influence on ecosystem functioning. Here, we report on the indirect influence of a pulsed resource, sugar maple (Acer saccharum) seed production, on nest survival in a migratory songbird. We hypothesized that seed production in year t would determine daily nest survival rate in year t + 1 through its effects on seed-eating rodents. We used the density of sugar maple seedlings (with cotyledons) in year t + 1 as a proxy for seed production in year t and predicted that it would be inversely related to songbird nest survival the same year. We estimated the density of sugar maple seedlings, eastern chipmunk (Tamias striatus) activity, and daily nest survival rate in the ovenbird (Seiurus aurocapilla) over four successive years in a northern hardwood forest of New Brunswick, Canada. Seedling density varied by two orders of magnitude between years, whereas an index of chipmunk activity changed by an order of magnitude. Both variables were positively correlated and negatively correlated to daily nest survival rate. A logistic-exposure model including only seedling density received the greatest level of support (lowest AICc). Previous studies have reported the effect of sugar maple masting on seed-eating rodent populations, but the strong link we report between seedling density and songbird nest survival is novel. A nocturnal seed-eating nest predator, deer mouse (Peromyscus maniculatus), was not considered in our models, which may explain why chipmunk was not the best predictor of daily nest survival rate. The trophic linkages we observed are remarkably strong for a temperate forest ecosystem and might become more prevalent in northeastern North America, at least on calcium-rich soils, with the loss of large-diameter beech trees as a result of beech bark disease.

Data from: Does wildlife resource selection accurately inform corridor conservation?

Evaluating landscape connectivity and identifying and protecting corridors for animal movement have become central challenges in applied ecology and conservation. Currently, resource selection analyses are widely used to focus corridor planning where animal movement is predicted to occur. An animal's behavioural state (e.g. foraging, dispersing) is a significant determinant of resource selection patterns, yet has largely been ignored in connectivity assessments. We review 16 years of connectivity studies employing resource selection analysis to evaluate how researchers have incorporated animal behaviour into corridor planning, and highlight promising new approaches for identifying wildlife corridors. To illustrate the importance of behavioural information in such analyses, we present an empirical case study to test behaviour-specific predictions of connectivity with long-distance dispersal movements of African wild dogs Lycaon pictus. We conclude by recommending strategies for developing more realistic connectivity models for future conservation efforts. Our review indicates that most connectivity studies conflate resource selection with connectivity requirements, which may result in misleading estimates of landscape resistance, and lack validation of proposed connectivity models with movement data. Our case study shows that including only directed movement behaviour when measuring resource selection reveals markedly different, and more accurate, connectivity estimates than a model measuring resource selection independent of behavioural state. Synthesis and applications. Our results, using African wild dogs as a case study, suggest that resource selection analyses that fail to consider an animal's behavioural state may be insufficient in targeting movement pathways and corridors for protection. This failure may result in misidentification of wildlife corridors and misallocation of limited conservation resources. Our findings underscore the need for considering patterns of animal movement in appropriate behavioural contexts to ensure the effective application of resource selection analyses for corridor planning.

opencc-zeroDec 2014View details →

Data from: Resources alter the structure and increase stochasticity in bromeliad microfauna communities

Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined.

opencc-zeroDec 2017View details →

Data from: Increase in light interception cost and metabolic mass component of leaves are coupled for efficient resource use in the high altitude vegetation

Global syntheses of leaf trait scaling relationships report an increase in light interception costs or 'diminishing returns' with increase in leaf area. However, variation in light interception costs across ecological gradients and plant strategies to cope up with these costs are not adequately understood. We analyzed leaf area (A) - leaf dry mass (M), leaf water mass (W) - M and W - A scaling relationships in plants occurring in a high altitude region of western Himalaya across environmental gradients to understand changes in light interception cost and metabolic mass component. M represents light interception cost, whereas, W is considered as a proxy of metabolic mass component for liquid phase being the ultimate source of metabolic activity. Trait values were measured from 9278 leaves belonging to 136 dominant species occurring at different sites, slope aspects, elevations and habitat types. Overall, light interception cost increased with increasing A (scaling exponent (α) <1 in A-M relationship) and metabolic mass component increased disproportionately high with increasing M and A. We found significant differences in scaling exponents of leaf trait relationship between sites, elevations, slope aspects and habitat types, indicating that increase in light interception cost was more evident at higher elevations, southern slopes and open habitats. Further, with increase in light interception cost, metabolic mass component also increased (α>1 in W-M and W-A relationships). The changes in scaling exponents of various leaf trait relationships across ecological gradients indicated that vegetation of different regions have differences in light interception cost and metabolic mass component. Moreover, increasing light interception cost (increase in mechanical and hydraulic tissues) with increasing A and increasing metabolic mass (leaf thickness) with increasing A and M are favored in high altitude vegetation. This could be a key strategy of high altitude plants for efficient resource capture and use in harsh environments.

Data from: Sunbird hovering behavior is determined by both the forager and resource plant

The long-standing paradigm that pollination systems adapted to hovering birds evolved only in the New World was recently challenged by the discovery of hovering pollination by Old World specialized passerine pollinators. This raises the possibility that hovering pollination may evolve more easily than previously believed, given sufficient selective pressure on plant traits, on nectarivory, or both. We observed foraging behavior by the sunbird Cyanomitra oritis at flowers of the native Old World plant Impatiens sakeriana. We measured the length of pedicels and peduncles (PedPed length), which can make the flowers difficult to reach while the bird perches on the stem, and determined if it influenced sunbird hovering or perching at a flower. Detailed analyses of video recordings showed that sunbirds only hovered at flowers with a long PedPed, whereas they employed both foraging modes when an adequate perch was available. A hovering sunbird could deplete nectar in a shorter time than a perching one. The frequency of visits was not greater at flowers with longer PedPed or with more open I. sakeriana flowers in the vicinity. Our study provides evidence that sunbird behavior does not follow simple energetic models, and that some sunbird pollination systems in the Old World resemble highly specialized hummingbird systems in the New World much more than expected, especially the overall adaptation of the system to bird hovering.

opencc-zeroDec 2019View details →

Data from: Generic and specific facets of vulnerability for analyzing trade-offs and synergies in natural resource management

1. The concept of vulnerability as the combination of exposure, sensitivity and adaptive capacity to a stressor is gaining traction outside of the climate realm, opening new avenues to address contemporary sustainability issues more holistically. Yet, critical notions that underpin vulnerability have yet to be integrated into its application to natural resource management and non-climatic stressors. In particular, the way generic and stressor-specific facets of vulnerability interact and can inform decision-makers about how interventions combine and/or trade-off remains unexplored. 2. Here, we investigate the salience of the generic/specific framing in the context of Chilean artisanal fishing communities engaged in rights-based co-management and experiencing pressures from two stressors: poaching and market volatility. Specifically, we draw on market data combined with socioeconomic surveys conducted with 446 members and leaders from 42 fisher unions to quantitatively investigate potential trade-offs and synergies between facets of vulnerability to poaching and markets. 3. Generic adaptive capacity (i.e. flexibility, assets, learning, organization and agency) likely facilitated stressor-specific adaptive capacities to both stressors. High levels of specific adaptive capacity to one stressor neither increased exposure nor undermined specific adaptive capacity to the other stressor. However, adaptive capacity did not translate into exposure reduction as expected, suggesting that adaptation barriers may prevent fishers from mobilizing adaptive capacity into effective adaptive action. 4. This study illustrates how breaking down vulnerability into generic and specific facets can help us better anticipate important trade-offs and synergies in management interventions. More generally, it highlights the potential of the climate adaptation and vulnerability literatures in informing place-based management of natural resources.

Data from: Higher resource level promotes virulence in an environmentally transmitted bacterial fish pathogen

Diseases have become a primary constraint to sustainable aquaculture, but remarkably little attention has been paid to a broad class of pathogens: the opportunists. Opportunists often persist in the environment outside the host and their pathogenic features are influenced by changes in the environment. To test how environmental nutrient levels influence virulence, we used strains of Flavobacterium columnare, an environmentally transmitted fish pathogen, to infect rainbow trout and zebra fish in two different nutrient concentrations. To separate the effects of dose and nutrients, we used three infective doses and studied the growth of bacteria in vitro. High nutrient concentration promoted both the virulence and the outside-host growth of the pathogen, most notably in a low-virulence strain. The increase in virulence could not be exhaustively explained by the increased dose under higher nutrient supply, suggesting virulence factor activation. In aquaculture settings, accumulation of organic material in rearing units can locally increase water nutrient concentration and therefore increase disease risk as a response to elevated bacterial density and virulence factor activation. Our results highlight the role of increased nutrients in outside-host environment as a selective agent for higher virulence and faster evolutionary rate in opportunistic pathogens.

Data from: Resource tracking and its conservation implications for an obligate frugivore (Procnias tricarunculatus, the three-wattled bellbird)

In Monteverde, Costa Rica, the vulnerable Three-wattled Bellbird (Procnias tricarunculatus) feeds primarily upon the fruit of Lauraceae species during its reproductive and post-reproductive seasons. To understand and advance appropriate conservation measures, this study identified the bellbird's foraging challenges in its search for a temporally and spatially fluctuating resource. Although there are at least 96 species of Lauraceae found in the five life zones of Monteverde, the distinct distributions of tree species both among and within life zones require the bellbirds to track seasonal fruiting across the various zones. In this six-year study, we monitored the fruiting of tree species and bellbird abundance in 24 study plots within its post-reproductive life zone, the Premontane Wet forest, in order to identify preferred bellbird food resources and how the fruiting of these species drives the spatial distribution of the bellbird. Our research revealed phenological patterns of annual, biennial, and triennial fruiting with high levels of fruiting synchrony within several identified key fruit species. Of critical conservation importance is that no single species of Lauraceae produced a consistent food supply for bellbirds each year. Therefore, even within life zones, the bellbird's survival depends on its mobility to search for and obtain fruit, as well as the availability of fruits of multiple tree species. The conservation implications include focused attention on multiple core areas within given life zones, protection of existing forest and remnant trees, and forest restoration with plantings of multiple tree species. We suspect that other tropical frugivorous species face similar conservation challenges.