Caenorhabditis nematodes colonize ephemeral resource patches in neotropical forests.

Factors shaping the distribution and abundance of species include life-history traits, population structure, and stochastic colonization-extinction dynamics. Field studies of model species groups help reveal the roles of these factors. Species of Caenorhabditis nematodes are highly divergent at the sequence level but exhibit highly conserved morphological uniformity, and many of these species live in sympatry on microbe-rich patches of rotten material. Here, we use field experiments and large-scale opportunistic collections to investigate species composition, abundance, and colonization efficiency of Caenorhabditis in two of the world's best studied lowland tropical field sites: Barro Colorado Island in Panamá and La Selva in Sarapiquí, Costa Rica. We observed seven species of Caenorhabditis, four of them known only from these collections. While these localities contain species from many parts of the phylogeny, both localities were dominated by globally distributed androdiecious species. We found that Caenorhabditis were able to colonize baits accessible only by phoresy, preferring to colonize baits making direct contact with the ground. We estimate founder numbers per colonization event to be low.

Network traits predict ecological strategies in fungi

Colonization of terrestrial environments by filamentous fungi relies on their ability to form networks that can forage for and connect resource patches. Despite the importance of these networks, ecologists rarely consider network features as functional traits because their measurement and interpretation are conceptually and methodologically difficult. To address these challenges, we have developed a pipeline to translate images of fungal mycelia, from both micro- and macro-scales, to weighted network graphs that capture ecologically relevant fungal behaviour. We focus on four properties that we hypothesize determine how fungi forage for resources, specifically: connectivity; relative construction cost; transport efficiency; and robustness against attack by fungivores. Constrained ordination and Pareto front analysis of these traits revealed that foraging strategies can be distinguished predominantly along a gradient of connectivity for micro- and macro-scale mycelial networks that is reminiscent of the qualitative ‘phalanx’ and ‘guerilla’ descriptors previously proposed in the literature. At one extreme are species with many inter-connections that increase the paths for multidirectional transport and robustness to damage, but with a high construction cost; at the other extreme are species with an opposite phenotype. Thus, we propose this approach represents a significant advance in quantifying ecological strategies for fungi using network information.

When are bacteria really gazelles? Comparing patchy ecologies with dimensionless numbers

From micro to planetary scales, spatial heterogeneity - patchiness - is ubiquitous in ecological systems, defining the environments in which organisms move and interact. While this fact has been recognized for decades, most large-scale ecosystem models still use spatially averaged "mean fields" to represent natural populations, while fine-scale, spatially explicit models are mostly restricted to particular organisms or systems. In a conceptual paper, Grunbaum (2012, Interface Focus 2: 150-155) introduced a heuristic framework, based on three dimensionless ratios quantifying movement, reproduction, and resource consumption, to characterize patchy ecological interactions and identify when mean-field assumptions are justifiable. In this paper, we calculated Grunbaum's dimensionless numbers for 33 real interactions between consumers and their resource patches in terrestrial, aquatic, and aerial environments. Consumers ranged in size from bacteria to blue whales, and patches lasted from minutes to millennia, spanning spatial scales of mm to hundreds of km. We found that none of the interactions could be accurately represented by a purely mean-field model, though 26 of them (79%) could be partially simplified by averaging out movement, reproductive, or consumption dynamics. Clustering consumer-resource pairs by their non-dimensional ratios revealed several unexpected dynamic similarities between disparate interactions. For example, bacterial Pseudoalteromonas exploit nutrient plumes in a similar manner to Mongolian gazelles grazing on ephemeral patches of steppe vegetation. Our findings suggest that dimensional analysis is a valuable tool for characterizing ecological patchiness, and can link the dynamics of widely different systems into a single quantitative framework.

Ecological stochasticity and phage induction diversify bacterioplankton communities at the microscale

In many natural environments, microorganisms self-assemble around heterogeneously distributed resource patches. The growth and collapse of populations on resource patches can unfold within spatial ranges of a few hundred micrometers or less, making such microscale ecosystems hotspots of biological interactions and nutrient fluxes. Despite the potential importance of patch-level dynamics for the large-scale evolution and function of microbial communities, we have not yet been able to delineate the ecological processes that control natural populations at the microscale. Here, we addressed this challenge in the context of microbially-mediated degradation of particulate organic matter by characterizing the natural marine communities that assembled on over one thousand individual microscale chitin particles. Through shotgun metagenomics, we found significant variation in microscale community composition despite the similarity in initial species pools across replicates. Strikingly, a subset of particles was highly populated by rare chitin-degrading strains; we hypothesized that their conditional success reflected the impact of stochastic colonization and growth on community assembly. In contrast to the conserved functional structures that emerge in ecosystems at larger scales, this taxonomic variability translated to a wide range of predicted chitinolytic abilities and growth returns at the level of individual particles. We found that predation by temperate bacteriophages, especially of degrader strains, was a significant contributor to the variability in the bacterial compositions and yields observed across communities. Our study suggests that initial stochasticity in assembly states at the microscale, amplified through biotic interactions, may have significant consequences for the diversity and functionality of microbial communities at larger scales.

Multiple responses of fine root resource uptake strategies to gravel content in a subtropical plantation

Most forest soils contain substantial amounts of gravel. However, unlike the more widely known root resource uptake behaviors which respond to resource patches in substrate without gravels, how roots respond to substrate containing different gravel levels is poorly understood. We grew roots in substrates with five gravel levels (0, 10, 20, 30, and 40% of volume) in a subtropical Schima superba plantation, determined fine root dynamics and turnover rate with minirhizotrons, measured fine root morphological, architectural, mycorrhizal colonization, chemistry, and mass allocation. The presence of gravel in the substrate delayed the timing of peak root growth. In the substrate with higher gravel content, plants produced more in roots in autumn, but there were fewer roots in summer and the roots tended to exhibit lower fine root turnover rate and mycorrhizal colonization, but higher root biomass allocation. The higher root biomass in the substrate with higher gravel content was associated with higher root carbon/nitrogen ratio. Our findings emphasize the complexity of root resource uptake behavior in response to gravel content and suggest that incorporating substrate gravel content into root studies may help to improve the prediction of patch exploitation and nutrient acquisition in stony soils.

Incubation mound-building by megapodes creates novel, high-resource patches in a semi-arid woodland

1.Desert ecosystems have sparse and heterogeneous resources. Discrete high-resource patches, associated with landscape modulators such as perennial vegetation, act as nutrient sinks in contrast to open, low-resource areas (interpatch matrix). In semi-arid mallee woodlands, malleefowl (Leipoa ocellata: Megapodiidae) create large incubation mounds by raking leaf litter and soil from high-resource patches to their mound sites in the interpatch matrix. Despite this conspicuous redistribution of resources, nothing is known about the physical and chemical properties of malleefowl mounds. 2.In this study, we measured groundcover, vegetation structure and composition, and soil chemistry at: malleefowl mounds, high-resource microsites modulated by trees, and in the low-resource interpatch matrix. The high and low-resource microsites were sampled near the mound in the potential Malleefowl disturbance zone, and outside of the disturbance zone. Mounds were classified into three age categories based on the number of years since they were active.3.We found that malleefowl mounds were a novel microsite, with soil chemistry more similar to tree-modulated patches and groundcover and vegetation variables more similar to the open, interpatch matrix. Additionally, the novel attributes of the mound persisted beyond 6 years from the last time the mound was active. The effect of malleefowl mound-building activities appeared to extend beyond recently used mounds, with vegetation suppressed in open patches close to the mound.4.Synthesis: Malleefowl redistribute resources from high-resource patches under trees to the open interpatch matrix. Incubation mound-building by animals can be a landscape modulating process via high-resource patch formation and is likely important for ecosystem functioning.

Fitness Landscapes Reveal Context-Dependent Benefits of Oviposition Choice

Resource choice behaviour has enormous fitness consequences and can drive niche expansion. However, individual behavioural choices are often mediated by past experience. Are such context-dependent behaviours adaptive? Using the red flour beetle, we demonstrate that context-dependent oviposition choice indeed reflects distinct, context-specific local fitness peaks. Manipulating female egg allocation in a habitat containing optimal and novel resource patches, we measured offspring fitness to generate fitness landscapes as a function of all possible oviposition behaviours (i.e. combinations of fecundity and resource preference). Females from different age and density contexts exhibit distinct behaviours that optimize different fitness components. With increasing age and experienced population density, they produce few but fast-developing offspring that are advantageous under high resource competition; whereas young naive females produce many slow-developing offspring, which is beneficial under weak competition. Systematically mapping complete context-dependent fitness landscapes is thus critical to infer behavioural optimality, and offers predictive power in novel contexts.

Ecological variation and institutionalized inequality in hunter-gatherer societies

Research examining institutionalized hierarchy tends to focus on chiefdoms and states, while its emergence among small-scale societies remains poorly understood. Here, we test multiple hypotheses for institutionalized hierarchy, using environmental and social data on 89 hunter-gatherer societies along the Pacific coast of North America. We utilize statistical models capable of identifying the main correlates of sustained political and economic inequality, while controlling for historical and spatial dependence. Our results indicate that the most important predictors relate to spatiotemporal distribution of resources. Specifically, higher reliance on and ownership of clumped aquatic (primarily salmon) versus wild plant resources is associated with greater political-economic inequality, measuring the latter as a composite of internal social ranking, unequal access to food resources, and presence of slavery. Variables indexing population pressure, scalar stress, and intergroup conflict exhibit little or no correlation with variation in inequality. These results are consistent with models positing that hierarchy will emerge when individuals or coalitions (e.g., kin groups) control access to economically defensible, highly clumped resource patches, and use this control to extract benefits from subordinates, such as productive labor and political allegiance in a patron–client system. This evolutionary ecological explanation might illuminate how and why institutionalized hierarchy emerges among many small-scale societies.

Stability Analysis of Delayed Age-Structured Resource-Consumer Model of Population Dynamics With Saturated Intake Rate

This article studies nonlinear n-resource-consumer autonomous system with age-structured consumer population. The model of consumer population dynamics is described by a delayed transport equation, and the dynamics of resource patches are described by ODE with saturated intake rate. The delay models the digestion period of generalist consumer and is included in the calorie intake rate, which impacts the consumer’s fertility and mortality. Saturated intake rate models the inhibition effect from the behavioral change of the resource patches when they react to the consumer population growing or from the crowding effect of the consumer. The conditions for the existence of trivial, semi-trivial, and non-trivial equilibria and their local asymptotic stability were obtained. The local asymptotic stability/instability of non-trivial equilibrium of a system with depleted patches is defined by new derived criteria, which relate the demographic characteristics of consumers with their search rate, growth rate of resource in patches, and behavioral change of the food resource when consumer population grows. The digestion period of a generalist consumer does not cause local asymptotical instabilities of consumer population at the semi-trivial and nontrivial equilibria. These theoretical results may be used in the study of metapopulation dynamics, desert locust populations dynamics, prey-predator interactions in fisheries, etc. The paper uses numerical experiments to confirm and illustrate all dynamical regimes of the n-resource-consumer population.

Importance of starting points in heterogeneous environments: interactions between two clonal plants with contrasting spatial architectures

Aims Plants can benefit from heterogeneous environments via disproportionately increasing resource harvesting in resource-rich patches. Their initial growing positions with respect to resource patches may thus have important influences on their performance and relative competitive ability. Such impacts may differ between species with contrasting spatial architectures. However, the potential influence of initial growing positions in heterogeneous environment on plant growth and competition has largely been ignored. Methods We grew the phalanx plant Carex neurocarpa and the guerrilla plant Bolboschoenus planiculmis alone or in competition in a heterogeneous environment consisting of high- and low-nutrient soil patches. In treatments without competition, one ramet of each species was grown in either a high- or a low-nutrient patch in the heterogeneous environment. In treatments with competition, a ramet of the target species was grown in either a high- or a low-nutrient patch, and a ramet of the competitor species was grown in the same patch as the target species or an adjacent patch with a different nutrient level. Important Findings Without competition C. neurocarpa produced more biomass and ramets when initially grown in a high-nutrient patch than when initially grown in a low-nutrient patch. With competition, these differences disappeared. Consequently, competitive intensity on C. neurocarpa was higher when it initially grew in a high-nutrient patch than when it initially grew in a low-nutrient patch. These impacts were independent of the initial position of its competitor. By contrast, the initial positions of B. planiculmis did not influence its growth or competitive response. Therefore, in heterogeneous environments, initial growing positions of clonal plants may influence their performance in competition-free environments and may also affect their relative competitive ability, and these effects may depend on spatial architecture of the plants.