Resource Gradients Research Articles

Mathematical Modelling of Spatially Inhomogeneous Non-Stationary Interaction of Pests with Transgenic and Non-Modified Crops Considering Taxis

Introduction. This paper addresses a unified spatially inhomogeneous, non-stationary model of interaction between genetically modified crop resources (corn) and the corn borer pest, which is also present on a relatively small section of non-modified corn. The model assumes that insect pests influence both types of crops and are capable of independent movement (taxis) towards the gradient of plant resources. It also considers diffusion processes in the dynamics of all components of the unified model, biomass growth, genetic characteristics of both types of plant resources, processes of crop consumption, phenomena of growth and degradation, diffusion, and mutation of pests. The model allows for predictive calculations aimed at reducing crop losses and increasing the resistance of transgenic crops to pests by slowing down the natural mutation rate of the pest. Materials and Methods. The mathematical model is an extension of Kostitsin’s model and is formulated as an initial-boundary value problem for a nonlinear system of convection-diffusion equations. These equations describe the spatiotemporal dynamics of biomass density changes in two types of crops — transgenic and non-modified — as well as the specific populations (densities) of three genotypes of pests (the corn borer) resulting from mutations. The authors linearized the convection-diffusion equations by applying a time-lag method on the time grid, with nonlinear terms from eachequation taken from the previous time layer. The terms describing taxis are presented in a symmetric form, ensuring the skew-symmetry of the corresponding continuous operator and, in the case of spatial grid approximation, the finite-difference operator. Results. A stable monotonic finite-difference scheme is developed, approximating the original problem with second-order accuracy on a uniform 2D spatial grid. Numerical solutions of model problems are provided, qualitatively corresponding to observed processes. Solutions are obtained for various ratios of modified and non-modified sections of the field. Discussion and Conclusion. The obtained results regarding pest behavior, depending on the type of taxis, could significantly extend the time for pests to acquire Bt resistance. The concentration dynamics of pests moving in the direction of the food gradient differs markedly from the concentration of pests moving towards a mate for reproduction.

Distribution pattern and driving factors of mite communities in karst cave ecosystems.

Mites are among the most abundant invertebrates in subsurface ecosystems, and their community assemblages and distributions are often significantly influenced by the diversity of habitat resources. The cave ecosystem encompasses drastic changes in nonbiological factors, such as changes in lighting conditions from bright to extraordinarily dark and habitat gradients of surface plant resources from abundant to scarce or even disappearing, providing an ideal unique environment for evaluating the assembly mechanism of soil animal communities. Nevertheless, there still needs to be a sufficient understanding of the biodiversity patterns and drivers of mite communities across environmental gradients in karst caves. We conducted a comprehensive survey on the composition and diversity of soil mites in three photometric zones (dark, twilight, and light) of a typical karst cave and its adjoining extractive environments (forest scrub and farmland). Our research aimed to investigate the ecological relationships of mite communities between above- and below-ground habitats and the effects of abiotic factors on mite communities. We collected 49 families, 86 genera, and 1284 mites. In the external cave environment, we captured 1052 mites from 72 genera and 45 families; in the internal cave environment, we captured 232 mites from 46 genera and 29 families. The abundance, richness of genera, and diversity parameters of the mite community decreased from the cave entrance to the cave interior with decreasing light intensity. Oribatid mites dominated the mite community. Protoribates and Scheloribates were the dominant genera, along with Tectocepheus and 11 other genera, which primarily distinguished the mite communities among different habitats. Forty endemic taxa were found in the external cave environment, compared to 14 endemic taxa in the internal cave environment. The mite community showed a strong preference for the cave ecosystem habitat. Temperature, humidity, and soil nitrogen content significantly influenced the distribution pattern of mite communities (VIP > 0.8, p < 0.05).

Spatial variability in the contribution of termites to the decay of plant detritus

AbstractDrylands are characterized by high spatial variability in resource availability due to sporadic rainfall, topography of the landscape and important effects of animals. Resource availability gradients may trigger patterns in decomposer population abundances and activity, which could affect ecosystem functions such as decomposition. Here, we examined the influence of resource availability gradients on the importance of termites in the decomposition of wood and grass litter. We placed wood blocks and grass litter baits in bags accessible and inaccessible to termites across wood and grass resource gradients as determined by the presence or absence of a top mammalian predator and across topographic gradients during a 9‐month period in arid Australia. We hypothesized that grass‐eating termite activity would track grass abundance and wood‐eating termite activity would track wood abundance. Termites were the predominant decomposition agent at these sites. Termites contributed to 99.5% of wood decomposition and 83.9% of grass decomposition during our study period. For wood, the termite effect was spatially variable and increased with habitat wood availability, which was greatest on dunes and where top predators were absent. However, the contribution of termites to grass litter decomposition did not track grass availability or termite abundance. The highest effects of termites on grass decomposition rates were found in habitats where the absence of top predators led to low grass availability. Our findings highlight how spatial variability in resources in addition to other factors that we do not document but are known to be influenced by the presence of top predators, such as insectivore predation rates, across the landscape could affect ecosystem functions such as decomposition.

Seasonal patterns and processes of migration in a long-distance migratory bird: energy or time minimization?

Optimal migration theory prescribes adaptive strategies of energy, time or mortality minimization. To test alternative hypotheses of energy- and time-minimization migration we used multisensory data loggers that record time-resolved flight activity and light for positioning by geolocation in a long-distance migratory shorebird, the little ringed plover, Charadrius dubius. We could reject the hypothesis of energy minimization based on a relationship between stopover duration and subsequent flight time as predicted for a time minimizer. We found seasonally diverging slopes between stopover and flight durations in relation to the progress (time) of migration, which follows a time-minimizing policy if resource gradients along the migration route increase in autumn and decrease in spring. Total flight duration did not differ significantly between autumn and spring migration, although spring migration was 6% shorter. Overall duration of autumn migration was longer than that in spring, mainly owing to a mid-migration stop in most birds, when they likely initiated moult. Overall migration speed was significantly different between autumn and spring. Migratory flights often occurred as runs of two to seven nocturnal flights on adjacent days, which may be countering a time-minimization strategy. Other factors may influence a preference for nocturnal migration, such as avoiding flight in turbulent conditions, heat stress and diurnal predators.

Mammalian community responses in relation to anthropogenic disturbances and resource gradients in the shade coffee forest ecosystem of Southwestern Ethiopia

Understanding the effects of variation in resource availability and habitat disturbance on the ecology of mammals is vital for successful conservation management. In this study, we examined how human disturbances, resource availability and elevation gradients influence mammal assemblages in both managed coffee forest and natural forest of the Belete-Gera National Forest Priority Area, southwestern Ethiopia. We surveyed mammals using motion-detecting infrared camera traps in 90 locations for a total of 4142 camera days. We measured distance from main roads and settlements as disturbance factors, and distance from water sources, key grazing sites, and forest edges and woody plant diversity as resource variables. We assessed the mammal assemblages in coffee forest and natural forests using generalized linear models. Further, we used linear modelling to compare the relationships of mammal detection rates by feeding guilds and body size to resource variables. In total, we recorded 8815 videos identifying 23 different mammal species. The mammal assemblages in coffee forests were negatively associated with increasing distances from key grazing sites, water sources, and elevation. In contrast, the association with increasing distance from the road and woody plant diversity was positive. In addition, herbivores and large (25–200 kg) and very large (≥200 kg) mammals, were all negatively associated with increasing distance from the natural forest edges. With the conversion of natural forest to coffee forest and the intensification of coffee forest management, sustainable management of key grazing sites, water sources, and diverse woody plant species will be essential to the conservation of mammals. In addition, to ensure mammal conservation, adjacent natural forests around coffee forests should also be protected.

Migration, movements, and survival in a partially migratory elk (Cervus canadensis) population

AbstractMigration provides an adaptive strategy to improve fitness by allowing individuals to exploit gradients of resources and changes in predation risk. In recent decades, the extent and prevalence of migration has declined in numerous ungulate species including many populations of elk (Cervus canadensis). Resident elk are often more closely associated with human activity, are more readily involved in agricultural conflicts and may contribute to overgrazing on some ranges. We evaluated migratory trends, survival rates, and causes of mortality in a partially migratory elk population in southeastern British Columbia, Canada, and compared these parameters with data from a 1982–1996 study from the same area. Analysis of 201 animal‐years (n = 78 collared cow elk) between 2016 and 2022 showed a ratio of 52% migratory to 48% resident elk, similar to what was found during the 1982–1996 study (55% migratory to 45% resident; n = 40 cows). Among the migrants, 55% were standard migrants (traveling moderate to longer distances and changing little in elevation), 35% elevational, and 10% mixed/atypical. We detected a 14% yearly switching rate between migratory and resident strategies. We recorded 30 mortalities: 47% from human causes, predominantly elk‐vehicle/train collisions (33% of mortalities), apparent starvation/old age (17%), and predation (17%). Notably, while mortality from natural causes was similar between strategies, human‐caused mortality was nearly twice as high in resident elk. Signs of nutritional stress and lower pregnancy rates indicated potential forage limitations. Migrants had higher average survival rates (0.90) compared to residents (0.83), a shift from the 1982–1996 study that recorded higher resident survival rates (0.98), the same migrant survival rate (0.90), and fewer elk‐vehicle/train collisions. Cow elk in our study made fewer and shorter movements into upper mountain tributaries and greater use of mine properties than observed during the 1982–1996 study. Wildlife managers should consider opportunities to enhance elk forage within traditional high‐elevation summer ranges and mitigations to reduce elk‐vehicle/train collisions. Further research is needed to quantify reproductive success, monitor calf survival, and determine relative forage quality among summering areas between migratory strategies, and determine winter ranges of long‐distant migrants.

A Study of the Influence of the Type of Land Use on the Enzymatic Activity of Soils in Southwestern China

Although soil enzyme activity can act as an effective indicator of soil nutrient status, there is some uncertainty about its accuracy within soil depth across different land uses. To assess the effects of different land uses on the interactions between soil enzyme activity and nutrient status within different soil horizons, in this study we examined soil total carbon (C), nitrogen (N), and phosphorus (P) concentrations, pH, and the activities of five hydrolytic (i.e., amylase, invertase, cellulase, acid phosphatase, and urease) and three oxidative enzymes (i.e., catalase, dehydrogenase, and phenol oxidase) involved in C, N, and P acquisition and evaluated their interactions within the topsoil (0–10 cm), subsoil (10–20 cm), and deeper soil layer (20–30 cm) under various land uses (i.e., rice field, cultivated land, bamboo plantation, forest land, and barren land). We found that the levels of hydrolytic enzyme activities and nutrient concentrations were higher in the topsoil than the deeper layer. The hydrolytic enzyme activities were positive correlated with soil C, N, and P concentrations, while the activities of oxidative enzymes showed strong associations with soil pH. Furthermore, the results of fuzzy comprehensive evaluation models suggest that the overall enzyme activity can serve as an indicator of soil nutrient status in the topsoil and subsoil, but not in the deeper layer. The depth-specific nature of soil enzyme–nutrient relationships may be attributed to different land-use management practices. Our study highlights the complex interactions between soil nutrients, pH, and enzyme activities within soil profiles, and soil enzyme activity as an indicator of soil nutrient status is depth-dependent across the different land uses. The specific functional groups of enzymes and the gradients of resources and environmental conditions within the soil profile that is partly mediated by land use play crucial roles in shaping these relationships. Our results can also provide some new insights into sustainable soil management practices under the background of intense anthropogenic activities and global change.

Microclimatic Influences on the Abundance of Three Non-Troglobiont Species

Subterranean environments are often characterized by a natural gradient of microclimatic conditions and trophic resources, showing a higher trophic availability and a lower microclimatic stability in the shallowest area (close to the cave entrance), while the opposite occurs in the deepest sections. The shallowest areas of subterranean environments (e.g., the entrance and twilight zone, Mesovoid Shallow Substratum) act as ecotones between the surface habitats and the deep areas, creating a particular habitat which can be exploited by numerous species with different degrees of adaptation to subterranean environments. Species living in these ecotones may hold a key role in sustaining the entire ecosystem, as they are likely one of the major drivers of allochthonous organic matter. Indeed, these species are usually facultative cave-dwellers, meaning that they are able to exit and forage on the surface. Once these species are back inside the cave, they provide the local community with different typologies of organic matter (e.g., feces, eggs), which represent one of the most important sources of organic carbon. Therefore, studying which ecological features may exert significant effects on the abundance of these species may be of great help in understanding the ecosystem dynamics and the functional role of each species. In this study we analyzed the data collected through a year-round monitoring program, aiming to assess the potential effects that both abiotic and biotic features may have on the abundance of three facultative cave species. We focused on seven caves located in Monte Albo (Sardinia, Italy). The cave environments were divided into 3-meter sectors, and within each cave sector, microclimatic and biological data were seasonally recorded. We focused on the following facultative cave species: the spiders Metellina merianae and Tegenaria sp. and the snail Oxychilus oppressus. Different relationships were observed between the ecological features and the abundance of the three species. The two spiders were more abundant in warmer cave sectors closer to the cave entrance, especially the M. merianae. On the other hand, the snail tended to be more abundant farther from the cave entrance and in more illuminated cave sectors, probably because sunlight promotes the abundance of some of its trophic resources (e.g., lichens, vegetation). Furthermore, O. oppressus was the only species whose abundance and cave distribution was significantly affected by seasonality. This study provides useful and novel information to understand the population dynamics of facultative cave species and their role in subterranean ecosystems.

Dynamics for a diffusive prey–predator model with advection and free boundaries

This article deals with a free boundary problem of the Lotka–Volterra type prey–predator model with advection in one space dimension. The model considered here may be applied to describe the expanding of an invasive or new predator species adopting a combination of random movement and advection upward or downward along the resource gradient, with the free boundaries representing expanding fronts of predator species. The main purpose of this article is to understand the influence of the advection environment on the dynamics of the model. We provide sufficient conditions for spreading and vanishing of the predator species, and we find a sharp threshold between the spreading and vanishing concerning this model. Moreover, for the case of successful spreading for the predator, we give estimates of asymptotic spreading speeds and nonlocal long‐time behavior of the prey and the predator.

Influence of local environmental gradients on ecological strategies of herbaceous communities in riverine side channels

AbstractQuestionsIn riverine side channels (secondary and former arms), the alternation of lotic, lentic and dry phases produces disturbance and resource gradients that filter species and community strategies. To better understand the impact of this alternation of functioning on plant communities at a fine spatial scale, we tested for the effects of elevation (linked to water level), slope, longitudinal position, light availability and sediment grain size on (i) taxonomic composition and (ii) competition, stress tolerance, and ruderal strategies (C, S and R strategies) at the community level. We hypothesized that fewer resources would increase the stress‐tolerant prevalence (i.e., community‐weighted mean value), while topographic gradients would affect ruderal prevalence. In addition, we hypothesized that strong and directional environmental filtering should reduce the co‐occurrence of species with different CSR strategy values (i.e., low C, S and R functional dispersion).LocationFourteen side channels on the lower reach of the Loire river (France).MethodsTaxonomic composition of the herb layer and environmental variables were assessed on 474 plots. The relations between species composition and environmental gradients were investigated by a constrained analysis of principal coordinates. The effects of environmental gradients on community CSR strategies were assessed using mixed‐effects models and a model‐averaging procedure.ResultsTaxonomic community composition was shaped mainly by light availability, topographic elevation and sediment grain size. Slope and the interaction between light and elevation influenced the community‐weighted mean and functional dispersion values of S and R strategies. Among other interactions, those involving sediment grain size shaped the dispersion values for C and R strategies.ConclusionThe study identified shading and fine sediment grain size as key drivers of biotic homogenization in the riverscape. Increasing the disturbance frequency and magnitude would limit the progression of the ecological succession and favor the co‐occurrence of taxonomically and functionally diverse communities within the side channels.

Collective action problems led to the cultural transformation of Sāmoa 800 years ago.

In this research we identify the processes leading to hierarchical society in a region of Sāmoa, the often-labelled 'birthplace' of the Polynesian chiefdoms. Our analyses in the Falefa Valley on 'Upolu island combine lidar mapping and ground survey to reveal an extensive system of archaeological features: rock walls, ditches, and platforms. Excavation and radiocarbon dating underpin a feature chronology and characterize feature variation. Soil nutrient analyses and geoarchaeological coring indicate spatial differences in the agricultural potentional of the valley and human modification of the environment over time. Our results demonstrate that the construction of large rock walls, some several hundred meters long, began approximately 900-600 years ago, shortly after rapid population rise in Sāmoa. This was followed by the building of small rock walls, often enclosing rectilinear fields or platforms. Both rock wall types are concentrated in the western and northern regions of the valley and greater rock wall densities are associated with areas of higher agricultural potential. The earliest wall construction was penecontemporaneous with partial forest removal that created a more productive wetland environment in the southeastern region of the valley, an area later a focus of agricultural ditching. We propose that with population rise the variable fertility of agricultural land became a significant resource gradient, influencing the population in two ways. First, areas of more fertile agricultural land promoted territorial behaviour, including large rock walls, and led to a collective action problem. Second, niche construction in the form of human-induced environmental change created a productive wetland agricultural system that was enhanced with a reticulate ditch network, the maintenance of which also led to a collective action problem. We conclude that in the Falefa Valley, the second largest catchment in Sāmoa, collective action problems were the cause of increased social hierarchy and may underlie the origins of chiefdoms throughout Polynesia.

Thermocline stratification favors phytoplankton spatial overlap and species diversity in a subtropical deep reservoir

Spatial segregation of species along opposing resource gradients is a major research topic in ecology as it enables the coexistence and maintenance of high diversity. Thermocline stratification causes heterogeneous resource distribution, however, the effect of thermocline stratification on phytoplankton dynamic in-depth profiles is still unclear. To understand the underlying mechanism behind the effects of thermocline stratification on phytoplankton species diversity in stratified lakes, the monthly changes in thermocline parameters, deep chlorophyll maxima (DCM) parameters, spatial overlap (SO) among major phytoplankton taxonomic groups, and phytoplankton species diversity were evaluated in Lake Qiandaohu in the Zhejiang Province of China from April 2017 to December 2018. Thermocline depth (TD) was significantly negatively related to thermocline strength (TS). The monthly air temperature was the main driver behind the thermocline and the seasonal thermal-stratification cycle was divided into two stratification stages. Significant linear relationships were observed between the DCM parameters (depth, concentration, and thickness) and TD during the strong stratification period. TD was significantly positively related to phytoplankton species diversity and the SO between Cryptophyta and Chlorophyta as well as between Cryptophyta and Bacillariophyta during weak stratification periods. Significant positive correlations were observed between SO and Shannon diversity during both periods. Structural equation modeling (SEM) showed that air temperature significantly decreased TD and increased species diversity by increasing SO during the strong stratification period. Strong stratification under warming favored the formation of shallower and thinner DCMs, leading to phytoplankton coexistence and maintenance of high species diversity through a preclusion of dominance. This study characterized the temporal dynamics of phytoplankton dynamic in-depth profiles in response to strong stratification from warming.

Animal-vectored nutrient flows across resource gradients influence the nature of local and meta-ecosystem functioning

Organisms move across landscapes mediating nutrient, energy, and biomass exchanges. Meta-ecosystem ecology offers a framework to study how these flows affect ecosystem functions in space and time. However, meta-ecosystem models often represent consumer movement as diffusion along gradients of resources. Crucially, this assumes that consumer movement connects the same trophic compartments among patches of the same ecosystem. Yet, empirical evidence shows that organisms move across different ecosystems and connect diverse trophic compartments in diffusive and non-diffusive ways. Here, we derive a two-patch meta-ecosystem model that accounts for both types of organismal movement, and we investigate their influences on local and meta-ecosystem functions. We apply a novel approach, modelling consumer movement through a dispersers’ pool that captures the fraction of moving organisms and allows us to partition local and regional dynamics. We show that non-diffusive consumer movement increases landscape heterogeneity while diffusive consumer movement enhances source–sink dynamics. Local ecosystem differences driven by consumer movement type are less prevalent at meta-ecosystem extents. Thus, movement type is essential for predicting local ecosystem dynamics. Our results support recent calls to consider explicitly the role of consumers in shaping and maintaining ecosystem functions across spatial extents.

Wildfire and cattle legacies on gradients of soil nitrogen underlie patterns of annual brome invasion.

Human activities are increasing wildfires and livestock activity in arid ecosystems with potential implications for the spread of invasive grasses. The objective of this study was to test whether fire history and cattle activity alter soil resource gradients, thereby affecting patterns of Bromus rubens L. (red brome) invasion. Six paired burned and unburned transect lines (1-km long) were established in the northeast Mojave Desert along the boundaries of four independent wildfire scars. At 100-m transect increment points, we measured the distance to the two nearest cowpats, and two random points and measured the density, height, biomass, and seed production of red brome, soil moisture and inorganic nitrogen (N). Cattle activity was 29% greater along burned transects compared to unburned transects (P < 0.05). Red brome height, density, and seed production were 11-34% greater along burned transects than unburned transects (P < 0.05). Red brome height, biomass, density, and seed production were twofold to tenfold greater next to cowpats compared to random points (P < 0.05). Soils along burned transects and beneath cowpats had greater soil inorganic N (P < 0.05), which was positively correlated with red brome density, height, biomass, and seed production (R2 = 0.60-0.85, P < 0.0001). Transgenerational effects were evident as seeds from red brome next to cowpats had 27% higher germination than seeds collected from random points. Positive responses of red brome to increased inorganic N related to fire and cattle activity may contribute fine fuel infill that drives invasive grass-fire cycles in deserts.

The carbon balance of plants: economics, optimization, and trait spectra in a historical perspective.

Over fifty years have passed since the publication of Harold Mooney's formative paper, "The Carbon Balance of Plants" on pages 315-346 of Volume 3 (1972) of Annual Review of Ecology and Systematics. Arguably, the conceptual framework presented in that paper, and the work by Mooney and his students leading up to the paper, provided the foundational principles from which core disciplines emerged in plant economic theory, functional trait theory and, more generally, plant physiological ecology. Here, we revisit the primary impacts of those early discoveries to understand how researchers constructed major concepts in our understanding of plant adaptations, and where those concepts are likely to take us in the near future. The discipline of functional trait ecology, which is rooted in the principles of evolutionary and economic optimization, has captured the imagination of the plant physiological ecology research community, though its emphasis has shifted toward predicting species distributions and ecological roles across resource gradients. In the face of 'big-data' research pursuits that are revealing trait expression patterns at the cellular level and mass and energy exchange patterns at the planetary scale, an opportunity exists to reconnect the principles of plant carbon balance and evolutionary optimization with trait origins at the genetic and cellular scales and trait impacts at the global scale.

The biogeography of embolism resistance across resource gradients in the Amazon

AbstractAimUnderstanding tree mortality under climate change‐induced droughts requires knowledge of hydraulic trait distribution across environmental gradients. The spatial distribution of embolism resistance (i.e., P50), a key trait linked to hydraulic failure, is currently unknown across the Amazon. Here, we tested how precipitation, water table depth (WTD) and soil fertility interact as filters modulating the geographic hydraulic trait distribution.LocationFour sites in three key regions across the Amazon basin: Central, Western peripheral area and Brazilian Shield.Time PeriodPresent.Major Taxa StudiedTree species.MethodWe measured hydraulic vulnerability curves of 64 tree species (165 individuals) using an orthogonal design contrasting seasonal precipitation gradients, soil fertility and WTD. To estimate the geographical distribution of hydraulic traits for the basin scale, we use the coefficients of the best generalized linear model, projected on a 1 km grid in each environmental layer.ResultsWe show that WTD and soil fertility are the main drivers of embolism resistance, while precipitation has a secondary effect. Trees in shallow WTD and fertile soils had riskier hydraulic strategies. Our spatial projection identified the Amazonian southern band and valleys across the basin as the most vulnerable areas. High soil fertility in these regions increases the variability of hydraulic traits and thus uncertainty in predictions of drought responses.Main ConclusionAt the scale of the Amazon basin, we show that dominant tree species traits converge toward hydraulic resistance when resource (water and nutrients) levels are low and towards hydraulic vulnerability (but with higher trait variability) when resources increase. These results highlight the importance of WTD and soil fertility in structuring hydraulic traits and their effects on tree mortality under climate change‐induced droughts. Further empirical tests covering a wider spatial range and more tree species will help validate our biogeographical distribution model.

Habitat coupling dynamics of mobile consumers along a freshwater and marine resource gradient in a sub-Arctic estuarine system

Food webs consist of numerous connections between consumers and resources that can couple adjacent ecosystems together by the movement of nutrients, prey, and consumers leading to habitat coupling. Habitat coupling and isotopic niche dynamics among mobile consumers at the individual and population-level has been examined extensively in freshwater systems but has received little attention in sub-Arctic estuaries, which act as transition zones between freshwater and marine habitats and resources. The objective of this study was to quantify the diet composition between freshwater-and marine-derived resources and the isotopic niche size of mobile consumers (13 fishes and 2 seal species) within the lower Churchill River, Manitoba, Canada using stable isotopes (δ13C, δ15N and δ34S) in a Bayesian framework. Cisco, lake whitefish, and northern pike represented the habitat couplers in this system and also exhibited the greatest amount of individual variability since most (75%, 56%, 65% of individuals for cisco, lake whitefish, and pike respectively) consumed a mix of both freshwater-and marine-derived resources. The largest isotopic niche sizes were found for lake whitefish and northern pike, whereas the smallest isotopic niche sizes were found for both harbour and ringed seals. The isotopic niche of lake whitefish overlapped with the most species (5 in total), which supports their broader use of both freshwater- and marine-derived resources. Habitat couplers in this system exhibited more variability in their foraging strategy than the other consumers, which aligns with their known life histories and migratory or resident movement strategies. Future changes in the relative availability of freshwater and marine-derived resources due to climate and anthropogenic stressors could pose consequences to these habitat coupling species and overall trophic dynamics of sub-Arctic estuarine systems.

Rhizomorph: The Coordinated Function of Shoots and Roots

Computer graphics has dedicated a considerable amount of effort to generating realistic models of trees and plants. Many existing methods leverage procedural modeling algorithms - that often consider biological findings - to generate branching structures of individual trees. While the realism of tree models generated by these algorithms steadily increases, most approaches neglect to model the root system of trees. However, the root system not only adds to the visual realism of tree models but also plays an important role in the development of trees. In this paper, we advance tree modeling in the following ways: First, we define a physically-plausible soil model to simulate resource gradients, such as water and nutrients. Second, we propose a novel developmental procedural model for tree roots that enables us to emergently develop root systems that adapt to various soil types. Third, we define long-distance signaling to coordinate the development of shoots and roots. We show that our advanced procedural model of tree development enables - for the first time - the generation of trees with their root systems.

The contribution of strong and weak ties to resilience: The case of small-scale maize farming systems in Mexico

CONTEXTThe relevance of social interactions (social ties) to farming systems' resilience is widely recognized. However, controversies exist around the contribution that farmers interacting with external actors (weak/bridging ties) versus with other farmers (strong/bonding ties) have in their resilience strategies through innovation. Farmers use different strategies to respond to their farming systems and contexts' particularities. Comparing the contribution of both strong and weak ties in different farming systems brings variety in resilience strategies. OBJECTIVETo generate evidence of the complementary contribution of social ties to resilience by comparing indexes associated with strong and weak ties from innovation networks of different farm types. METHODSThis paper applies an ego-centric social network analysis to farm units characterized by a farm typology to compare their strong/bonding and weak/binding ties contribution to innovation networks. It uses data from 29,796 farm units of maize smallholders in different regions from Central and Southern Mexico covering the gradient from commercial to subsistence farming. The analysis estimates two indexes based on actors' similarity/dissimilarity, that are External and Internal and Specialization Indexes. RESULTS AND CONCLUSIONSOur findings quantify differential contributions of strong versus weak ties to resilience strategies associated with innovation networks among different types of small-scale maize farmers. They demonstrate how differences among five farm types regarding farm resources access, maize production systems and farmers' social attributes influence their innovation networks. A gradient exists between farm types in their innovation network indexes regarding the contribution of strong versus weak ties. Commercial farmers, as the winners of the modernization process, have better access to resources and establish a wider variety of relationships with weak ties. However, interactions with other farmers are essential for technology adoption. In contrast, weak ties represented by institutions have a minor participation in innovation networks of diversified income and subsistence farm units. Strong ties dominate these farm types producing maize for consumption as part of their persistence strategies. Low-mechanized and elder family farm types, affected by geographic remoteness and population ageing processes, represent intermediate points in the gradient of farm resources and network indexes. SIGNIFICANCEJointly farm typology and social network approaches open new avenues to enhance farming system resilience. These approaches show how farmers establish their social interactions for innovation, creating specific combinations of strong and weak ties that are farm type specific. Diverse resilience strategies appear from these combinations involving not only adaptation but also persistence strategies that require further exploration.

Arbuscular mycorrhiza changes plant facilitation patterns and increases resource use efficiency in intercropped annual plants

Arbuscular mycorrhizal fungi (AMF) play a vital role in mediating rhizosphere interactions and plant growth, especially in resource-constrained soils. However, few studies have documented the effects of AMF on plant–plant interaction patterns and resource use efficiency along stress gradients. In this study, a growth environment-controlled experiment was carried out to evaluate the effects of AMF inoculation on maize-grass pea intercropping along three phosphorus (P) and two water gradients. The data indicated that soil water and P availability determined the plant interspecific interaction pattern, and that interaction was strongly mediated by AMF inoculation. Grass pea and maize were mutually facilitated under low P and water conditions and transitioned to a new pattern, i.e., that maize was facilitated but grass pea was neutral role or facilitator with increasing resource availability. The facilitative effect was particularly significant under P- and water-deficient conditions. Moreover, the transition of the plant–plant interaction pattern was mechanically driven by improving rhizospheric phosphatase activities by 5.08–20.02 %, rhizospheric acidification and enhanced microbial activities under resource deficit conditions. Critically, AMF inoculation was observed to significantly improve rhizospheric soil P availability and microbial biomass (p < 0.05); however, it enhanced the complementary utilization of P and water and weakened interspecific competition under high-resource conditions. Therefore, AMF inoculation positively transformed the plant–plant interaction pattern along resource gradients for higher P, nitrogen and water use efficiency. This study validates the context-dependent interspecific interaction and the role of AMF in optimizing resource use in a nutrient-impoverished intercropping system.