Consumer-resource theory predicts dynamic transitions between outcomes of interspecific interactions

Interactions between two populations are often defined by their interaction outcomes; that is, the positive, neutral, or negative effects of species on one another. Yet, signs of outcomes are not absolute, but vary with the biotic and abiotic contexts of interactions. Here, we develop a general theory for transitions between outcomes based on consumer–resource (C–R) interactions in which one or both species exploit the other as a resource. Simple models of C–R interactions revealed multiple equilibria, including one for species coexistence and others for extinction of one or both species, indicating that species' densities alone could determine the fate of interactions. All possible outcomes [(+ +), (+ −), (−−), (+ 0), (− 0), (0 0)] of species coexistence emerged merely through changes in parameter values of C–R interactions, indicating that variation in C–R interactions resulting from biotic and abiotic conditions could determine shifts in outcomes. These results suggest that C–R interactions can provide a broad mechanism for understanding context- and density-dependent transitions between interaction outcomes.     

Tertiary succession: a new concept to help vegetation restoration

Restoration is the human activity of manipulating vegetation with the aim of accelerating attainment of stable vegetation. But current procedures seem to arrest succession instead. A comparison of primary and secondary successions with restoration activities suggests there is little overlap in these concepts. Thinking of the process of restoration as a tertiary succession helps highlight managerial options which may improve success, especially by addressing environmental and biological legacies.     

A model-based approach to detect interspecific interactions during biofilm development

A model-based approach was developed to detect interspecific interactions during biofilm development. This approach relied on the comparison of experimental data with a simple null model of biofilm growth dynamics where individual species grew independently of one another, except that they competed for space. Such a model was directly parameterized with a 4D confocal image series of biofilms and then used as a null model to detect interspecific interactions between pairs of bacterial species. This approach was tested in two bispecific competitive trials. In the first trial, the progressive exclusion of Pseudomonas fluorescens by Pseudomonas putida appeared to be due solely to the different intrinsic growth rates of the two strains. In contrast, modelling results suggested the presence of interference competition between Pseudomonas aeruginosa and P. putida in mixed biofilms. The authors’ approach enables the detection of ecologically relevant interactions which constitute a prerequisite to building a comprehensive view of the dynamics and functioning of spatially structured bacterial communities.     

Indirect interactions between two aphid species in relation to ant attendance

The influence of foraging by the ant, Lasius niger, on the population growth of two aphid species, Lachnus tropicalis and Myzocallis kuricola, on chestnut trees, Castanea crenata, was examined. The ant-tending effect was divergent depending on the aphid density per ant: it was positive when there were few aphids per ant, but negative when there were many aphids per ant. In addition, the density of one aphid species also influenced the ant-tending effect on the other aphid. Furthermore, the influences were asymmetrical: an increase in L. tropicalis density per ant reversed the ants effect on this species and on M. kuricola, while an increase in M. kuricola per ant did not significantly influence the ants effect on L. tropicalis. Thus, the ant seems to stabilize the L. tropicalis population density and keep this species from extinction, while the ants effect on M. kuricola depends on the density of L. tropicalis and may lead M. kuricola to extermination. This change in the ant-tending effect corresponds to the previously detected density-dependent change in predation activity of the ants on aphids. In contrast, the density-dependent change in the protection effect of the ants against natural enemies does not explain the results.     

Intra- and interspecific facilitation in mangroves may increase resilience to climate change threats

Mangroves are intertidal ecosystems that are particularly vulnerable to climate change. At the low tidal limits of their range, they face swamping by rising sea levels; at the high tidal limits, they face increasing stress from desiccation and high salinity. Facilitation theory may help guide mangrove management and restoration in the face of these threats by suggesting how and when positive intra- and interspecific effects may occur: such effects are predicted in stressed environments such as the intertidal, but have yet to be shown among mangroves. Here, we report the results of a series of experiments at low and high tidal sites examining the effects of mangrove density and species mix on seedling survival and recruitment, and on the ability of mangroves to trap sediment and cause surface elevation change. Increasing density significantly increased the survival of seedlings of two different species at both high and low tidal sites, and enhanced sediment accretion and elevation at the low tidal site. Including Avicennia marina in species mixes enhanced total biomass at a degraded high tidal site. Increasing biomass led to changed microenvironments that allowed the recruitment and survival of different mangrove species, particularly Ceriops tagal.     

密度、物种比例对盐沼植物种子萌发阶段种内、种间相互作用的影响

种间相互作用是影响湿地植物群落构建的关键因子,其形式、强度和机制可能随着生长发育的过程而发生改变。种子萌发是植物生命周期的关键环节,一定程度上决定了植物种群分布和群落结构。野外种子萌发过程受到邻近同种或异种种子间相互作用的影响,但对于种子萌发过程中种内、种间相互作用强度及其影响因素的了解仍十分有限。该研究通过培养皿萌发实验探讨了种子密度(每皿80粒、每皿160粒)及比例(单种、3:1混种、2:2混种、1:3混种)对互花米草(Spartina alterniflora)、海三棱藨草(Scirpus×mariqueter)、芦苇(Phragmites australis)种子萌发率、平均萌发时间的影响,并采用相对邻株效应(RNE)评估了这3个物种的种内、种间相互作用强度。结果表明,密度对互花米草、海三棱藨草、芦苇种子的萌发率均有一定的促进作用。与互花米草混种时,芦苇种子在占比最低(25%)处理下的平均萌发时间显著长于单种及其他混种比例处理。3种植物种子的竞争能力没有明确的等级关系,存在非传递性竞争,萌发时海三棱藨草相对互花米草具有一定的竞争优势,互花米草相对芦苇具有一定优势,而芦苇的竞争能...     

Tiger and leopard co-occurrence: intraguild interactions in response to human and livestock disturbance

Intraguild interactions have important implications for carnivore demography and conservation. Differences in how predators respond to different forms of disturbance might alter their interaction patterns. We sought to understand how human and livestock disturbance impact co-occurrence of sympatric large carnivores such as tiger (Panthera tigris) and leopard (P. pardus) and thereby mediate the intraguild interaction pattern to enable coexistence of the species in a human-dominated landscape. We surveyed 361 locations in Chitwan National Park, Nepal, to examine how prey abundance and disturbance factors such as human and livestock presence might influence habitat use by tigers and leopards independently and when co-occurring. Single-species single-season models and two-species single-season models were developed to examine hypotheses on unconditional detection and occupancy and species interaction respectively. Pervasive human use of the park had negative impacts on tiger occupancy while the abundance of prey had a positive influence. Despite significant prey overlap between tigers and leopards, none of the native prey species predicted leopard habitat occupancy. However, habitats used extensively by livestock were also used by leopards. Further, we found strong evidence of intraguild competition. For instance tiger occupancy was higher in prey-rich areas and leopard occupancy was low in the sites where tigers were present. These findings, and a species interaction factor of < 1 clearly indicate that leopards avoid tigers, but their use of areas of disturbance enables them to persist in fringe habitats. We provide empirical evidence of how intraguild interaction may result in habitat segregation between competing carnivores, while also showing that human and livestock use of the landscape create disturbance patterns that facilitate co-occurrence of the predators. Thus, because large carnivores compete, some disturbance may mediate coexistence in small protected areas. Understanding such interactions can help address important conservation challenges associated with maintaining diverse carnivore communities in small or disturbed landscapes.     

Anomalous outbreaks of an invasive defoliator and native bark beetle facilitated by warm temperatures,changes in precipitation and interspecific interactions

Biotic disturbance agents such as insects can be highly responsive to climatic change and have widespread ecological and economic impacts on forests. Quantifying the responses of introduced and native insects to climate, including how dynamics of one agent may mediate those of another, is important for forecasting disturbance and associated impacts on forest structure and function. We investigated drivers of outbreaks by larch casebearer Coleophora laricella, an invasive defoliator, and eastern larch beetle Dendroctonus simplex, a native, tree‐killing bark beetle, on tamarack Larix laricina from 2000 to in Minnesota, USA. We evaluated the utility of temporal, spatial and climatic variables in predicting the presence/absence of outbreaks of each insect in cells of rasterized aerial survey data. The role of defoliation by larch casebearer in outbreaks of eastern larch beetle was also investigated. For both species, the most important predictors of outbreak occurrence were proximity of conspecific outbreaks in space and time. For larch casebearer, outbreak occurrence was positively associated with spring precipitation and warmer growing seasons. Outbreak occurrence of eastern larch beetle was positively associated with warmer and dryer years and was more likely in cells with prior defoliation by larch casebearer. Our results demonstrate that climate can drive large scale outbreaks of introduced and non‐native disturbance agents on a single host species, and that interactions at the tree level between such agents may scale up to manifest across large temporal and spatial scales.     

Many ways to make darker flies: Intra‐ and interspecific variation in Drosophila body pigmentation components

Body pigmentation is an evolutionarily diversified and ecologically relevant trait with substantial variation within and between species, and important roles in animal survival and reproduction. Insect pigmentation, in particular, provides some of the most compelling examples of adaptive evolution, including its ecological significance and genetic bases. Pigmentation includes multiple aspects of color and color pattern that may vary more or less independently, and can be under different selective pressures. We decompose Drosophila thorax and abdominal pigmentation, a valuable eco‐evo‐devo model, into distinct measurable traits related to color and color pattern. We investigate intra‐ and interspecific variation for those traits and assess its different sources. For each body part, we measured overall darkness, as well as four other pigmentation properties distinguishing between background color and color of the darker pattern elements that decorate each body part. By focusing on two standard D. melanogaster laboratory populations, we show that pigmentation components vary and covary in distinct manners depending on sex, genetic background, and temperature during development. Studying three natural populations of D. melanogaster along a latitudinal cline and five other Drosophila species, we then show that evolution of lighter or darker bodies can be achieved by changing distinct component traits. Our results paint a much more complex picture of body pigmentation variation than previous studies could uncover, including patterns of sexual dimorphism, thermal plasticity, and interspecific diversity. These findings underscore the value of detailed quantitative phenotyping and analysis of different sources of variation for a better understanding of phenotypic variation and diversification, and the ecological pressures and genetic mechanisms underlying them.     

Influence of macronutrient imbalance on native ant foraging and interspecific interactions in the field

1. Ants interact with a diversity of organisms. These interactions, coupled with their abundance, cause ants to have ecologically important effects across multiple trophic levels. 2. Empirical study of ant nutritional ecology has led to the prediction that a macronutrient imbalance will affect ant behaviour and interspecific interactions that underlie these broad‐scale effects. Excess carbohydrate relative to protein is predicted to increase ant aggressiveness, predatory tendency and foraging activity, and to decrease collection of hemipteran honeydew and plant nectar. 3. In field experiments conducted in 2009 and 2010, captive colony fragments of a native ant, Formica podzolica (Hymenoptera: Formicidae), were provided with either simulated prey or carbohydrate solution ad libitum. Foraging behaviours and interactions with flowers, myrmecophilous aphids and aphid natural enemies on wild‐grown plants were documented. 4. Strong effects of macronutrient imbalance on foraging manifested quickly and consistently across colonies; in accordance with predictions, prey‐fed foragers collected both honeydew and floral nectar, whereas carbohydrate‐fed ants ceased collecting these resources. Counter to predictions, carbohydrate‐fed ants dramatically lowered their activity levels and did not prey upon aphids. 5. Ants had no effect on aphid enemies in 2009, when the latter were relatively rare, but decreased their abundance in 2010. Despite this protection, the net effect of ants on aphids was negative (measured only in 2009). Prey‐fed ants demonstrated a strong preference for honeydew over floral nectar, thus demonstrating that a macronutrient imbalance may lead to different interactions with similar resources. 6. This study links ant nutrition and community ecology by demonstrating the rapid, asymmetric and multitrophic consequences of nutritionally mediated behaviour.     

Resistance to temperature extremes in sub-Antarctic weevils: interspecific variation, population differentiation and acclimation

Much of the work on the responses of terrestrial arthropods to high and low temperatures has been done on model organisms such as Drosophila . However, considerable variation in thermotolerance is partitioned at the family level and above, raising questions about the broader applicability of this work to other taxa. Here we investigate resistance to high and low temperatures, following different temperature treatments, in ten species and 31 populations of weevils found on sub-Antarctic Heard Island and Marion Island, which have substantially different climates. In these weevils there is considerable interspecific and among-population variation in critical thermal minimum (CTmin) and critical thermal maximum (CTmax), but most of this variation in critical limits can be ascribed to phenotypic plasticity. We find no relationship between CTmin and CTmax at the species level, and this is true also of populations and of responses to the temperature treatments. In general, plastic (acclimation) changes in CTmin are larger than those in CTmax. Our data therefore provide support for the idea that resistance to heat and to cold are decoupled in terrestrial arthropods. Furthermore, our results suggest that investigations of physiological limits to species borders should incorporate the effects of phenotypic plasticity on physiological capabilities.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 401–414.     

Resistance and resilience of stream insect communities to repeated hydrologic disturbances after a wildfire

1. Wildfires are often followed by severe, sediment‐laden floods in burned catchments. In this study, we documented resistance and resilience of stream insect communities to repeated postfire flash floods in a ‘burned stream’. We employed a before‐after‐control‐impact (BACI) design, where communities in comparable reaches of a burned stream and a reference stream were sampled from 2 years before, to 6 years after, a crown wildfire in north‐central New Mexico. 2. The first 100‐year flood following the 1996 Dome wildfire reduced total insect density and taxon richness to near zero in the burned stream. Despite showing low resistance, density returned rapidly to prefire levels because of colonisation by simuliids, chironomids and the mayfly Baetis tricaudatus. In general, taxa that were generalist feeders (collectors) with strong larval dispersal dominated communities in early postfire years with repeated, moderate flash floods. 3. Taxon richness and community composition were less resilient to postfire hydrologic disturbances. Taxon richness did not recover until floods dampened 4 years after the fire. Despite hydrologic recovery, composition in the burned stream still differed from prefire and reference stream compositions after 6 years postfire. A unique assemblage, dominated by taxa with strong larval or adult dispersal, was established after flash floods abated. Specialist feeders (shredders and grazers) that were common in prefire years were reduced or absent in the postfire assemblage. 4. Community succession in the burned stream was explained by the interaction between species traits, geographic barriers to colonisation and hydrologic conditions after the fire. Comparable changes in insect density, taxon richness, community composition and trait representation were not found in the reference stream, providing strong evidence that repeated postfire flash floods shaped community responses in the burned stream.     

Chemical contents of Macaranga food bodies: adaptations to their role in ant attraction and nutrition

1. Macaranga (Euphorbiaceae) is a paleotropical tree genus comprising myrmecophytic and non-myrmecophytic species. All species are presumed to possess food bodies (FBs) to maintain or attract ants as anti-herbivore defence.
2. The hypothesis was tested that Macaranga species differing in their mode of association with ants would produce FBs differing in their chemical composition. We investigated contents of carbohydrates, proteins and lipids in FBs of four myrmecophytic and one non-myrmecophytic Macaranga as well as one Parthenocissus (Vitaceae) species.
3. On a dry weight basis, FBs of myrmecophytes contained relatively higher amounts of proteins compared to carbohydrates than those of non-myrmecophytes. Soluble carbohydrates showed species-specific patterns and were found in especially high amounts in both non-myrmecophytes. Furthermore, Parthenocissus FBs contained higher amounts of soluble compared to polymerous substances not only in carbohydrates but also in proteins.
4. FBs seem to be specifically adapted to their respective role in ant attraction and nutrition, with myrmecophytes providing ants with high amounts of lipids and proteins and non-myrmecophytes mainly offering carbohydrates in the form of common soluble sugars.     

Tolerance and resilience of forest species to frost in restoration planting in southern Brazil

Listing potential species for restoring areas has become a complex task considering the lack of information regarding the silvicultural behavior of native trees after planting and their responses to environmental conditions. Frost is an important meteorological phenomenon that regulates the distribution of plant species, especially in subtropical regions. Thus, we evaluated the effect of frost and the resilience potential of native forest species in restoration planting of a riparian forest in southern Brazil. The experimental design used was randomized blocks in a 6 × 2 factorial scheme (6 species and 2 containers). During the winter in 2014 (270 days after planting), the damage from the impact of frost was assessed through a rating scale ranging from 0 (100% of the leaf area and damaged stem) to 10 (no visual damage). In addition, to assess species resilience, the height and stem diameter were measured, prior to the winter of 2014 and at 270 and 360 days. Eugenia involucrata and Schinus terebinthifolius were considered frost tolerant species. Parapiptadenia rigida was classified as moderately frost tolerant, while Casearia sylvestris, Cupania vernalis, and Inga vera were very sensitive to frost. Casearia sylvestris, E. involucrata, P. rigida, and S. terebinthifolius showed potential for recommencement of growth. On the other hand, C. vernalis and I. vera were considered too sensitive to frost, with high mortality rates and/or no resilience potential.