Biotic Forces Research Articles

Integrating ecological niche modeling and rates of evolution to model geographic regions of mimetic color pattern selection

Geographic variation in natural selection derived from biotic sources is an important driver of trait evolution. The evolution of Müllerian mimicry is governed by dual biotic forces of frequency-dependent predator selection and densities of prey populations consisting of conspecifics or congeners. Difficulties in quantifying these biotic forces can lead to difficulties in delimiting and studying phenomena such as mimicry evolution. We explore the spatial distribution of morphotypes and identify areas of high mimetic selection using a novel combination of methods to generate maps of mimetic phenotype prevalence in Ranitomeya poison frogs, a group of frogs characterized by great phenotypic variation and multiple putative Müllerian mimic pairs. We categorized representative populations of all species into four major recurring color patterns observed in Ranitomeya: striped, spotted, redhead, and banded morphs. We calculated rates of phenotypic evolution for each of the 4 morphs separately and generated ecological niche models (ENMs) for all species. We then split our species-level ENMs on the basis of intraspecific variation in color pattern categorization, and weighted ENM layers by relative evolutionary rate to produce mimicry maps. Our phenotypic evolutionary rate analyses identified multiple significant shifts in rates of evolution for the spotted, redhead, and banded phenotypes. Our mimicry maps successfully identify all suspected and known areas of Müllerian mimicry selection in Ranitomeya from the literature and show geographic areas with a gradient of suitability for Müllerian mimicry surrounding mimic hotspots. This approach offers an effective hypothesis generation method for studying traits that are tied to geography by explicitly connecting evolutionary patterns of traits to trends in their geographic distribution, particularly in situations where there are unknowns about drivers of trait evolution.

Deciphering Biotic and Abiotic Mechanisms Underlying Straw Decomposition and Soil Organic Carbon Priming in Agriculture Soils Receiving Long-Term Fertilizers.

Straw-related carbon (C) dynamics are central for C accrual in agro-ecosystems and should be assessed by investigating their decomposition and soil organic carbon (SOC) priming effects. Our understanding of biotic and abiotic mechanisms underpinning these two C processes, however, is still not sufficiently profound. Soils that had received organic and mineral fertilizers for 26 years were sampled for a 28 day incubation experiment to assess 13C-labeled straw decomposition and SOC priming effects. On the basis of analyzing physicochemical properties, fungal taxonomic (MiSeq sequencing) and functional (metagenomics) guilds, we quantified the contributions of biotic and abiotic attributes to straw decomposition and SOC priming. Here, we propose two distinct mechanisms underlying straw decomposition and SOC priming in agriculture soils: (i) accelerated straw mineralization in manure-treated soils was mainly driven by biotic forces, while (ii) larger SOC priming in NPK-amended soils was through abiotic regulation.

Shifts in population density centers of a hibernating mammal driven by conflicting effects of climate change and disease.

Populations wax and wane over time in response to an organism's interactions with abiotic and biotic forces. Numerous studies demonstrate that fluctuations in local populations can lead to shifts in relative population densities across the geographic range of a species over time. Fewer studies attempt to disentangle the causes of such shifts. Over four decades (1983-2022), we monitored populations of hibernating Indiana bats (Myotis sodalis) in two areas separated by ~110 km. The number of bats hibernating in the northern area increased from 1983 to 2011, while populations in the southern area remained relatively constant. We used simulation models and long-term weather data to demonstrate the duration of time bats must rely on stored fat during hibernation has decreased in both areas over that period, but at a faster rate in the northern area. Likewise, increasing autumn and spring temperatures shortened the periods of sporadic prey (flying insect) availability at the beginning and end of hibernation. Climate change thus increased the viability of northern hibernacula for an increasing number of bats by decreasing energetic costs of hibernation. Then in 2011, white-nose syndrome (WNS), a disease of hibernating bats that increases energetic costs of hibernation, was detected in the area. From 2011 to 2022, the population rapidly decreased in the northern area and increased in the southern area, completely reversing the northerly shift in population densities associated with climate change. Energy balance during hibernation is the singular link explaining the northerly shift under a changing climate and the southerly shift in response to a novel disease. Continued population persistence suggests that bats may mitigate many impacts of WNS by hibernating farther south, where insects are available longer each year.

Keystone predatory protists are associated closely with ammonia‐oxidizing microorganisms in an acidic Ultisol

AbstractPredatory protists are widely recognized as critical biotic forces driving soil microbial communities, but their top‐down controls on ammonia‐oxidizing microorganisms (AOMs), the major players in nitrification, are largely unresolved. Here, we investigated the communities of predatory protists and their associations with AOMs using high‐throughput sequencing and network analysis in soil aggregates following various long‐term organic substitutions. We found that organic substitutions increased while soil aggregation decreased the alpha diversity of predatory protists. Predatory protistan communities were significantly associated with AOMs. Variosea, an important group of Amoebozoa, were the keystone predatory protists associated with the AOMs. Collectively, our findings highlight the importance of predatory protists, especially Variosea, in regulating the communities of AOMs in an acidic Ultsisol, with implications for managing nitrification by predatory protists in agricultural soils.

Zooplankton variability and possible oceanographic anomalies from 1996 to 2009 on the south coast of Brazil.

The analysis of 14 years of sampling data on the zooplankton community in southern Brazil showed a tendency toward increased density and reduced species richness. This behavior could be a response to a prolonged period of negative sea surface temperature (SST) anomalies in the Pacific Ocean and the ENSO phenomenon. The persistence of the La Niña phenomenon between 2001 and 2008 was associated with a higher incidence of stress from southwest winds and a greater reach of the front of the La Plata River plume, with possible responses being lower temperatures in the summer/autumn and lower salinities in the winter/spring in the study area. Under these conditions, one response in the zooplankton community was larger copepod domains. This group was responsible for specific changes in the community, with an increase in the population of Acartia tonsa while populations of species with more thermophilic characteristics showed a decrease. It cannot be disregarded, however, that possible interactions between different abiotic and biotic forces acting in the environment may have influenced the structure of the community. It remains unknown whether a new steady state has been established in the environment or whether there has been a return to initial conditions.

Intertidal zonation of hemichordates in soft sediments

AbstractIntertidal zonation of organisms is well studied on rocky shores but less so in soft sediment communities. On rocky shores, communities are two dimensional, with biotic factors such as competition and predation setting the lower bound of a zone, whereas abiotic factors such as desiccation set the upper bound. In soft sediment communities, these patterns persist, but with a dynamic three‐dimensional ecosystem occupied by mobile infaunal organisms, zonation can be more difficult to quantify and detect. Hemichordate worms, however, deposit fecal casts at the surface, which can be easily identified and counted, making them a potential model system for identifying zonation in soft‐sediment systems. Here, we describe the intertidal zonation of hemichordate worms at two sites in Maine and Virginia. In Virginia,Saccoglossus kowalevskiioccurs in the mid‐intertidal at densities up to 500 individuals per square meter, whereas a tube‐building polychaete,Spiochaetopterus oculatus, dominates the lower intertidal. In Maine, two hemichordate species,Saccoglossus bromophenolosusandProtoglossus graveolens, co‐occur at densities up to 100 individuals per square meter in the mid‐intertidal, whereas hermit crabs and errant polychaetes are numerically dominant in the low intertidal. Despite known chemical defenses, crustaceans readily consumed hemichordates in lab assays, although polychaetes did not. In a field tethering experiment, loss rates of hemichordate‐flavored agarose pellets increased as tidal height decreased, suggesting that the lower bound of the hemichordate zone could be set by biotic forces such as crustacean predation. Additionally, a field transplant experiment found low survivorship of hemichordates transplanted to the upper intertidal, suggesting that desiccation may set their upper bound. These results are broadly consistent with prior studies of zonation in soft sediments, and expand our limited understanding of basic hemichordate ecology.

Soil aggregate isolation method affects interpretation of protistan community

Soil protists are major biotic forces driving microbial dynamics within aggregates. Interpretation of protistan spatial distribution and ecological processes in aggregates primarily relies on aggregate isolation methods. However, comparative studies illustrating how isolation methods influence protistan communities are lacking. Here, two isolation procedures, dry- and wet-sieving, were evaluated. The wet-sieving led to separation of dry mega-aggregates, which consequently altered aggregate size distribution and associated protistan communities. The variable influences of sieving methods on aggregate protists were dependent on soil type. However, the aggregate isolation method did not affect the prominent aggregate-effects on protistan communities and detection of dominant taxa. Collectively, our findings highlight the importance of isolation procedures for exploring the spatial heterogeneity of protists at the micro-level.

Co-occurrences of tropical trees in eastern South America: disentangling abiotic and biotic forces

Species co-occurrences in local communities can arise independent or dependent on species’ niches. However, the role of niche-dependent processes has not been thoroughly deciphered when generalized to biogeographical scales, probably due to combined shortcomings of data and methodology. Here, we explored the influence of environmental filtering and limiting similarity, as well as biogeographical processes that relate to the assembly of species’ communities and co-occurrences. We modelled jointly the occurrences and co-occurrences of 1016 tropical tree species with abundance data from inventories of 574 localities in eastern South America. We estimated species co-occurrences as raw and residual associations with models that excluded and included the environmental effects on the species’ co-occurrences, respectively. Raw associations indicate co-occurrence of species, whereas residual associations indicate co-occurrence of species after accounting for shared responses to environment. Generally, the influence of environmental filtering exceeded that of limiting similarity in shaping species’ co-occurrences. The number of raw associations was generally higher than that of the residual associations due to the shared responses of tree species to the environmental covariates. Contrary to what was expected from assuming limiting similarity, phylogenetic relatedness or functional similarity did not limit tree co-occurrences. The proportions of positive and negative residual associations varied greatly across the study area, and we found a significant tendency of some biogeographical regions having higher proportions of negative associations between them, suggesting that large-scale biogeographical processes limit the establishment of trees and consequently their co-occurrences.

Dynamics of data availability in disease modeling: An example evaluating the trade-offs of ultra-fine-scale factors applied to human West Nile virus disease models in the Chicago area, USA.

BackgroundSince 1999, West Nile virus (WNV) has moved rapidly across the United States, resulting in tens of thousands of human cases. Both the number of human cases and the minimum infection rate (MIR) in vector mosquitoes vary across time and space and are driven by numerous abiotic and biotic forces, ranging from differences in microclimates to socio-demographic factors. Because the interactions among these multiple factors affect the locally variable risk of WNV illness, it has been especially difficult to model human disease risk across varying spatial and temporal scales. Cook and DuPage Counties, comprising the city of Chicago and surrounding suburbs, experience some of the highest numbers of human neuroinvasive cases of WNV in the United States. Despite active mosquito control efforts, there is consistent annual WNV presence, resulting in more than 285 confirmed WNV human cases and 20 deaths from the years 2014–2018 in Cook County alone.MethodsA previous Chicago-area WNV model identified the fifty-five most high and low risk locations in the Northwest Mosquito Abatement District (NWMAD), an enclave ¼ the size of the combined Cook and DuPage county area. In these locations, human WNV risk was stratified by model performance, as indicated by differences in studentized residuals. Within these areas, an additional two-years of field collections and data processing was added to a 12-year WNV dataset that includes human cases, MIR, vector abundance, and land-use, historical climate, and socio-economic and demographic variables, and was assessed by an ultra-fine-scale (1 km spatial x 1 week temporal resolution) multivariate logistic regression model.ResultsMultivariate statistical methods applied to the ultra-fine-scale model identified fewer explanatory variables while improving upon the fit of the previous model. Beyond MIR and climatic factors, efforts to acquire additional covariates only slightly improved model predictive performance.ConclusionsThese results suggest human WNV illness in the Chicago area may be associated with fewer, but increasingly critical, key variables at finer scales. Given limited resources, these findings suggest large variations in model performance occur, depending on covariate availability, and provide guidance in variable selection for optimal WNV human illness modeling.

Diversity and functional structure of soil animal communities suggest soil animal food webs to be buffered against changes in forest land use

Forest soil and litter is inhabited by a diverse community of animals, which directly and indirectly rely on dead organic matter as habitat and food resource. However, community composition may be driven by biotic or abiotic forces, and these vary with changes in habitat structure and resource supply associated with forest land use. To evaluate these changes, we compiled comprehensive data on the species composition of soil animal communities and environmental factors in forest types varying in land-use intensity in each of three regions in Germany, i.e., coniferous, young managed, old managed, and unmanaged beech forests. Coniferous forests featured high amounts of leaf litter and low microbial biomass concentrations contrasting in particular unmanaged beech forests. However, soil animal diversity and functional community composition differed little between forest types, indicating resilience against disturbance and forest land use. Structural equation modelling suggested that despite a significant influence of forest management on resource abundance and quality, the biomass of most soil fauna functional groups was not directly affected by forest management or resource abundance/quality, potentially because microorganisms hamper the propagation of nutrients to higher trophic levels. Instead, detritivore biomass depended heavily on soil pH. Macrofauna decomposers thrived at high pH, whereas mesofauna decomposers benefitted from low soil pH, but also from low biomass of macrofauna decomposers, potentially due to habitat modification by macrofauna decomposers. The strong influence of soil pH shows that decomposer communities are structured predominantly by regional abiotic factors exceeding the role of local biotic factors such as forest type.

Long-term changes in the plant ecology of an African savanna landscape and the implications for ecosystem theory and conservation management

BackgroundStudies of the African savannas have used national parks to test ecological theories of natural ecosystems, including equilibrium, non-equilibrium, complex adaptive systems, and the role of top-down and bottom-up physical and biotic forces. Most such studies have excluded the impact of pastoralists in shaping grassland ecosystems and, over the last half century, the growing human impact on the world’s rangelands. The mounting human impact calls for selecting indicators and integrated monitoring methods able to track ecosystem changes and the role of natural and human agencies. Our study draws on five decades of monitoring the Amboseli landscape in southern Kenya to document the declining role of natural agencies in shaping plant ecology with rising human impact.ResultsWe show that plant diversity and productivity have declined, biomass turnover has increased in response to a downsizing of mean plant size, and that ecological resilience has declined with the rising probability of extreme shortfalls in pasture production. The signature of rainfall and physical agencies in driving ecosystem properties has decreased sharply with growing human impact.We compare the Amboseli findings to the long-term studies of Kruger and Serengeti national parks to show that the human influence, whether by design or default, is increasingly shaping the ecology of savanna ecosystems. We look at the findings in the larger perspective of human impact on African grasslands and the world rangelands, in general, and discuss the implications for ecosystem theory and conservation policy and management.ConclusionsThe Amboseli study shows the value of using long-term integrated ecological monitoring to track the spatial and temporal changes in the species composition, structure, and function of rangeland ecosystems and the role of natural and human agencies in the process of change. The study echoes the widespread changes underway across African savannas and world’s rangelands, concluding that some level of ecosystem management is needed to prevent land degradation and the erosion of ecological function, services, and resilience. Despite the weak application of ecological theory to conservation management, a plant trait-based approach is shown to be useful in explaining the macroecological changes underway.

Density dependence and habitat heterogeneity regulate seedling survival in a North American temperate forest

Survival and growth of forest tree seedlings are influenced by many abiotic and biotic forces that may vary across space and time. The simultaneous influences of habitat heterogeneity, temporal environmental variability (including disturbance regimes), and biotic interactions are difficult to disentangle, yet understanding the relative importance of these factors for tree seedling dynamics is critical for conservation of forest biodiversity. Most long term, spatially explicit studies of tree seedling ecology have been set in the tropics; much less attention has been given to tree seedlings in temperate forests. We monitored the survival of over 3000 individual seedlings over an eight-year period in a temperate forest in northeast Wisconsin, USA. Results from four seedling censuses demonstrated that both conspecific density and environmental variables significantly affected seedling survival. Higher densities of conspecific trees consistently reduced the probability of seedling survival over time. At the community level, relatively common species were negatively influenced by neighboring conspecific trees and exhibited higher per capita and per basal area mortality. The negative impacts of high conspecific tree density were most pronounced in areas of higher light and moisture, but these interactions varied over time, as did the importance of other abiotic variables. Patterns of less common species were more clearly explained by abiotic variables, with shifting relevance of specific variables according to species abundance. Conspecific negative density dependence, which interacts with resource gradients, and habitat conditions that shift over time are influencing community composition in this northern temperate forest.

Phylogenomic analyses reveal a Palaeozoic radiation and support a freshwater origin for clitellate annelids

AbstractClitellata is a major clade of Annelida comprising nearly all freshwater and terrestrial annelids as well as several marine species. We investigated clitellate phylogenetic relationships using transcriptomes sampled from 74 taxa (64 clitellates and 10 polychaetes), including multiple representatives of nearly all major clitellate higher taxa (Branchiobdellida, Capilloventridae, Crassiclitellata, Enchytraeidae, Haplotaxidae, Hirudinida, Lumbriculida, Moniligastridae, Naididae, Parvidrilidae, Phreodrilidae, Propappidae and Randiellidae). We used a number of filtered data matrices and phylogenetic analyses to examine the effects of data partitioning, missing data and compositional and branch‐length heterogeneity and used the resulting phylogenies for divergence time estimation and ancestral habitat reconstructions. All analyses and filtering methods produced a consistent, strongly supported topology in which (a) Enchytraeidae, Hirudinida, Hirudinea (here, Branchiobdellida plus Hirudinida), Lumbriculida, Lumbriculata (Lumbriculida plus Hirudinea), Phreodrilidae and Naididae are monophyletic, (b) a Parvidrilidae + Randiellidae clade is sister to the rest of Clitellata, (c) Phreodrilidae is sister to Naididae, (d) Haplotaxidae is non‐monophyletic, with some haplotaxids grouping with Crassiclitellata + Moniligastridae, (e) the Phreodrilidae + Naididae clade is sister to all other clitellates except Parvidrilidae + Randiellidae and Capilloventridae, and (f) Lumbriculata is sister to the Crassiclitellata + Moniligastridae + Haplotaxidae (in part) clade. Ancestral habitat reconstructions and divergence time analysis suggested that the most recent common ancestor of Clitellata lived in freshwater during the Devonian (419–359 million years ago) and that all major extant clitellate lineages arose over the next ~150 million years, with multiple lineages subsequently returning to marine habitats or invading land. This study provides a phylogenetic framework for further investigation of the geological, environmental and biotic forces and genomic changes that may have impacted clitellate evolution and enabled several major habitat transitions within this group.

Niche construction theory can link bark beetle-fungus symbiosis type and colonization behavior to large scale causal chain-effects.

Bark beetles form a variety of symbioses with fungi. Recent studies reveal how the fungi influence beetle nutrition and detoxify tree defenses and provide insight into why these symbioses vary so greatly in their outcomes, not only for host and symbiont, but also for the forest ecosystems within which they exist. Here, I review recent advances in our knowledge of these systems. I then introduce how niche construction theory can provide a framework to use this knowledge to better understand how different symbiosis types result in a gradient of ecosystem effects ranging from massive and durable to those of little ecological consequence.

Geomorphometric characterisation of natural and anthropogenic land covers

The scientific community has widely discussed the role of abiotic and biotic forces in reshaping the Earth’s surface. Currently, the literature is debating whether humans are leaving a topographic signature on the landscape. Apart from the influence of humans on processes, does the resulting landscape bear an unmistakable signature of anthropogenic activities? This research analyses from a statistical point of view the morphological signature of anthropogenic and natural land covers in different topographic context, as a fundamental challenge in the emerging debate of human-environment relationships and the modelling of global environmental change. It aims to explore how intrinsically small-scale processes, related to land use, can influence the form of entire landscapes and to determine whether these processes create a distinctive topography. The work focusses on four study areas in floodplains, plain to hilly, hills and mountains, for which LiDAR-derived Digital Terrain Models (DTMs) are available. Surface morphology is described with different geomorphometric parameters (slope, mean curvature and surface peak curvature) and their frequency distribution. The results show that the distribution of geomorphometric indices can reveal anthropogenic land covers and landscapes. In most cases, different land covers show statistically significant differences (p < 0.05) in their morphology. Finally, this study demonstrates the possibility to use a geomorphic analysis to quantify anthropogenic impact based on land covers in different landscape contexts. This provides useful insight into understanding the impact of human activities on the present morphology and offers a comprehensive understanding of coupling human-land interaction from a geomorphological point of view.

Ecological determinants of community structure across the trophic levels of freshwater food webs: a test using bromeliad phytotelmata

Understanding the relative importance of habitat and biotic drivers on community assembly across food web components is an important step towards predicting the consequences of environmental changes. Because documenting entire food webs is often impractical, this question has been only partially investigated. Here, we partitioned variation in species assemblages of the major components of tank bromeliad food webs (bacteria, algae, protozoans, detritivorous and predatory invertebrates) into habitat and biotic determinants and examined the influence of habitat variables and predator or prey abundance on all taxonomic assemblages. Ecological determinism of assemblage structure ranged from weak in bacteria (< 10% of the explained variance) to strong in predatory invertebrates (90%). Habitat features and canopy openness significantly influenced species assemblages; however, prey or predator density had far and away the most significant structuring effects. If biotic forces are at least as important as the abiotic forces while the importance of stochasticity declines towards upper trophic levels, then trophic levels could respond differently to natural or anthropogenic disturbance and to shifts in species distributions. The effects of such differential responses on food web reconfiguration, however, remain to be elucidated.

Outbreaks, coexistence, and life cycle of jellyfish species in relation to abiotic and biological factors along a South American coast

Olindias sambaquiensis and Rhacostoma atlanticum are the most abundant species of macrohydromedusae on the southern coast of Brazil; the first is associated with outbreaks of stings in bathers during the summer, and the second with interference in fishing. Due to their direct relationship with human activities, their life cycles were investigated, using laboratory cultivation and study of their cohorts in the field, as well as the patterns of abundance in light of the abiotic and biotic factors of the study area. The coexistence of the two species is possible due to differences in their life cycles, duration of the polyp phase, and the formation of well-defined cohorts. Variations in abundance of the species from one year to another cannot be explained by abiotic variables alone, such as seawater temperature, but may also be associated with the balance between these and other biotic forces, such as local production and, possibly, effects of competition between species. However, on a monthly scale, the aggregations of O. sambaquiensis in southern Brazil appear to be associated with the lowest frequency of north quadrant winds, which could, in addition to promoting resurgence processes, lead to dispersion of the organisms off the coast.

Determinants of predation success: How to survive an attack from a rattlesnake

Abstract The selection pressures that arise from capturing prey and avoiding predators are some of the strongest biotic forces shaping animal form and function. Examining how performance (i.e., athletic ability) affects the outcomes of encounters between free‐ranging predators and prey is essential for understanding the determinants of predation success rates and broad scale predator–prey dynamics, but quantifying these encounters in natural situations is logistically challenging. The goal of our study was to examine how various metrics of predator/prey performance determine predation success by studying natural predator–prey interactions in the field with minimal manipulation of the study subjects. We used high‐speed video recordings of free‐ranging sidewinder rattlesnakes (predator, Crotalus cerastes) and desert kangaroo rats (prey, Dipodomys deserti) to study how performance at various stages of their encounters alters the outcome of their interactions. We found that predation success depends on (a) whether the rattlesnake struck accurately, (b) if the rattlesnake strike was accurate, the reaction time and escape manoeuvres of the kangaroo rat, and (c) if the kangaroo rat was bitten, the ability of the kangaroo rat to use defensive manoeuvres to avoid subjugation by the snake. The results of our study suggest that the role of performance in predator–prey interactions is complex, and the determinants of predation success are altered by both predator and prey at multiple stages of an interaction in ways that may not be apparent in many experimental contexts. A plain language summary is available for this article.

Insolation and disturbance history drive biocrust biodiversity in Western Montana rangelands

Background and AimsBiological soil crust (biocrust) communities, though common and important in the intermountain west, have received little research attention. There are gaps in understanding what influences biocrust species’ abundance and distributions in this ecoregion. Climatic, edaphic, topographic, and biotic forces, in addition to anthropogenic disturbance can all influence the biocrust.MethodsWe determined the relative influence of several possible environmental filters in biocrust communities of western Montana (USA) grasslands at two spatial scales. The larger scale exploited strong topographically-dictated climatic variation across >60km2, while the smaller scale focused on differences among distinct microsites within ~700m2 plots.ResultsWe detected a total of 96 biocrust taxa, mostly lichens. Biocrust richness at each site ranged from 0 to 39 species, averaging 14 species. Insolation, aspect, and disturbance history were the strongest predictors of biocrust richness, abundance, and species turnover across the landscape; soil texture was influential for some biocrust community properties. Steep, north-facing slopes that receive longer periods of shade harbored higher diversity and cover of biocrust than south-facing sites. At a small scale, interspaces among native herbaceous communities supported the greatest diversity of biocrust species, but microsites under shrub canopies supported the greatest cover.ConclusionsWe found that, among the variables investigated, tillage, insolation, soil texture and the associated vegetation community were the most important drivers of biocrust abundance and species richness. This study can inform the practice of restoration and conservation, and also guide future work to improve predictions of biocrust properties.

Back to the Origin: In Situ Studies Are Needed to Understand Selection during Crop Diversification

Crop domestication has been embraced as a model system to study the genetics of plant evolution. Yet, the role of the environment, including biotic forces such as microbial and insect communities, in contributing to crop phenotypes under domestication and diversification has been poorly explored. In particular, there has been limited progress in understanding how human selection, agricultural cultivation (soil disturbance, fertilization, and irrigation), and biotic forces act as selective pressures on crop phenotypes. For example, geographically-structured pathogenic, pestiferous, and mutualistic interactions with crop plants have likely given rise to landraces that interact differently with local microbial and insect communities. In order to understand the adaptive role of crop traits, we argue that more studies should be conducted in the geographic centers of origin to test hypotheses on how abiotic, biotic, and human selective forces have shaped the phenotypes of domesticated plants during crop domestication and subsequent diversification into landraces. In these centers of origin, locally endemic species associated with wild ancestors have likely contributed to the selection on plant phenotypes. We address a range of questions that can only be studied in the geographic center of crop origin, placing emphasis on Mesoamerican polyculture systems, and highlight the significance of in situ studies for increasing the sustainability of modern agricultural systems.