Ecological Field Experiments Research Articles

Spatial memory obviates following behaviour in an information centre of wild fruit bats.

According to the information centre hypothesis (ICH), colonial species use social information in roosts to locate ephemeral resources. Validating the ICH necessitates showing that uninformed individuals follow informed ones to the new resource. However, following behaviour may not be essential when individuals have a good memory of the resources' locations. For instance, Egyptian fruit bats forage on spatially predictable trees, but some bear fruit at unpredictable times. These circumstances suggest an alternative ICH pathway in which bats learn when fruits emerge from social cues in the roost but then use spatial memory to locate them without following conspecifics. Here, using an unique field manipulation and high-frequency tracking data, we test for this alternative pathway: we introduced bats smeared with the fruit odour of the unpredictably fruiting Ficus sycomorus trees to the roost, when they bore no fruits, and then tracked the movement of conspecifics exposed to the manipulated social cue. As predicted, bats visited the F. sycomorus trees with significantly higher probabilities than during routine foraging trips (of >200 bats). Our results show how the integration of spatial memory and social cues leads to efficient resource tracking and highlight the value of using large movement datasets and field experiments in behavioural ecology. This article is part of the theme issue 'The spatial-social interface: a theoretical and empirical integration'.

Effect of genotype-environment interaction on some important quality parameters of common wheat (Triticum aestivum L.)

Abstract. In ecological field experiment involving common wheat varieties, several quality parameters were analyzed, which express different aspects of grain quality. Objective of the study was to establish in detail the main relations about the influence of the conditions (location and year) and their interaction with the genotype on each of the parameters, separately. The accepted hypothesis was that the growing conditions have a different strength and direction of effect on each parameter, which should ultimately be reflected in a unique way on the performance of each variety of the studied group. In four locations, which represent a sample of the main grain-producing regions of the country, twenty-four varieties of common winter wheat were investigated. Five indexes of grain quality were analyzed as follows: Sedimentation index (Zeleny); Deformation energy (W); P/L alveograph configuration ratio (P/L); Swelling index (G); Dough stability time (Dstab). All possible aspects of the interaction of genotype (GEN), environment (ENV) as well as the interaction between them (GEN*ENV) were investigated. Statistical approaches and methods that are specialized for this purpose were used. Each of the three main factors – “location”, “year” and “genotype” influenced the variation of the group of varieties through the changes of the conditions, independently and in combination with each other. In this combination of effects expressed as (GEN*ENV) the most essential role was the “location”. The established significant interaction caused an adequate (linear) and inadequate (non-linear) change of the varieties, relative to those of the conditions. For the majority of parameters, this change was mostly linear (PC1=70%), with the exception of the P/L (alveograph configuration ratio), where both effects had parity (PC1≈PC2-4). The environments in the locations during individual seasons had high degree of repeatability (H2=0.75 – 0.94), which allows a high degree of prediction of the values of each single parameter. All parameters were affected to varying degrees by the studied factors and the interaction between them. The influence of the conditions was relatively the strongest on the Dough stability time index (Dstab), and the Swelling index (G) was most closely related to the genetic predisposition of the variety. The effects of the interaction of the genotype with the environments (GEN*ENV) made up about 20-30% of the total variation of three of the parameters, for Deformation energy index (W) the effect reached 40%, and for the Dough stability time index (Dstab) it was only about 13%. The environments during the seasons were the cause of a dynamic change of the correlations between the yield and some of the parameters, in some of the locations studied. Probably, this was directly dependent on the specific combination between the levels of extraction and the level of a given parameter.

A nondestructive method of calculating the wing area of insects.

Most insects engage in winged flight. Wing loading, that is, the ratio of body mass to total wing area, has been demonstrated to reflect flight maneuverability. High maneuverability is an important survival trait, allowing insects to escape natural enemies and to compete for mates. In some ecological field experiments, there is a need to calculate the wing area of insects without killing them. However, fast, nondestructive estimation of wing area for insects is not available based on past work. The Montgomery equation (ME), which assumes a proportional relationship between leaf area and the product of leaf length and width, is frequently used to calculate leaf area of plants, in crops with entire linear, lanceolate leaves. Recently, the ME was proved to apply to leaves with more complex shapes from plants that do not have any needle leaves. Given that the wings of insects are similar in shape to broad leaves, we tested the validity of the ME approach in calculating the wing area of insects using three species of cicadas common in eastern China. We compared the actual area of the cicadas’ wings with the estimates provided by six potential models used for wing area calculation, and we found that the ME performed best, based on the trade‐off between model structure and goodness of fit. At the species level, the estimates for the proportionality coefficients of ME for three cicada species were 0.686, 0.693, and 0.715, respectively. There was a significant difference in the proportionality coefficients between any two species. Our method provides a simple and powerful approach for the nondestructive estimation of insect wing area, which is also valuable in quantifying wing morphological features of insects. The present study provides a nondestructive approach to estimating the wing area of insects, allowing them to be used in mark and recapture experiments.

Instrumental variable methods in structural equation models

Abstract Instrumental variable regression (RegIV) provides a means for detecting and correcting parameter bias in causal models. Widely used in economics, recently several papers have highlighted its potential utility for ecological applications. Little attention has thus far been paid to the fact that IV methods can also be implemented within structural equation models (SEMIV). In this paper I present the motivations, requirements and basic procedures for using SEMIV. I first consider causal inference and IVs from the perspective of a randomized experiment with partial control of the cause of interest. I consider common sources of bias, the role of randomization and limits to its capacity to exclude bias. Sources of bias include omitted confounders, reciprocal causation, reverse causation and measurement error, all of which can all be seen as a single problem—endogeneity. The approach to estimating IV models most commonly used in econometric practice, two‐stage least squares regression (2SLS), is explained, followed by a brief exposition of the covariance modelling approach used in SEM. Using data from an ecological field experiment, I illustrate the use of the treatment variable as an IV and then illustrate procedures for evaluating candidate variables that might serve as additional IVs. IV methods are shown to be useful for both detecting endogeneity and removing its influences. I illustrate some of the ways that bias can be generated, as well as diagnostic capabilities and means for remedy embedded within SEM. Procedures for screening and evaluating additional IVs reveal valuable lessons regarding the theoretical requirements and empirical standards for IVs. SEMIV provides a useful way to detect and control for bias. I suggest that the use of IVs within the SEM framework can support the simultaneous pursuit of causal inference and explanatory modelling, a common pair of aspirations for ecologists. Moving forward, there is a need for a better understanding of the capabilities of SEMIV and requirements for successful application.

Temporal variation in effect sizes in a long-term, split-plot field experiment.

Ecological field experiments initiate successional and evolutionary changes among resident species, yet effect sizes are often reported as if they were constants. Few ecological studies have addressed their questions through long-term, experimental approaches, and many questions remain unanswered regarding temporal patterns in ecological effect sizes. We document temporal variation in effect sizes in response to pulse and press manipulations in a long-term factorial field experiment at Nash's Field, England. The experiment comprises seven treatments applied in a split-plot design to test the single and interactive effects of herbivory by insects, molluscs, and rabbits, liming, nutrient limitation (applied as press experiments), competition (exclusion of grasses or herbs with specific herbicides), and seed limitation (pulse experiments) on plant community dynamics. The response of all vascular plant species was followed for two decades. High species richness was positively related to the minus-grass herbicide in the first decade and negatively related to both nitrogen addition and the abundance of dominant species in both decades. Many significant effects appeared quickly, but some large effects were not detected until year 15. Press experiments produced some long-lasting effects, but effect sizes changed due to both idiosyncratic "year effects" and secular trends. For pulse experiments, most effects, including positive and negative responses to herbicide application and the invasion of most of the sown species, disappeared quickly. However, some endured or grew monotonically, such as the invasion of two sown species that benefited from particular combinations of the press treatments. The fastest effects to appear were the responses from established species. Many of these responses were negative, likely resulting from reduced niche dimensionality and competitive exclusion by new dominant species. Contrarily, one of the largest community-level effects took well over a decade to appear: the natural invasion by one species, which responded to a four-way interaction between experimental treatments. The insights gained from individual effects increased with the duration of the lag before their first appearance, drawing attention to the importance of long-term, manipulative field experiments. This experiment also reinforces the point that factorial experiments are the most insightful way to explore ecological interactions.

Investigating the consequences of climate change under different land‐use regimes: a novel experimental infrastructure

AbstractClimate change and land‐use change are considered as the most important threats to ecosystems. Both factors can be expected to have interacting influences on ecosystem functions directly and indirectly via changes in biodiversity. Knowledge about these interactions is limited due to a lack of experiments which investigate climate change effects under different land‐use scenarios. Among the processes involved in ecosystem responses to global change, in particular, those occurring in soils or related to biotic interactions and microevolution were underinvestigated in previous experiments. Examinations of these relationships require spatial and temporal scales which go beyond those realized in the majority of ecological field experiments. We introduce a new research facility, the Global Change Experimental Facility (GCEF), which was designed to investigate the consequences of a future climate scenario for ecosystem functioning in different land‐use types on large field plots (400 m2). Climate manipulation is based on projections for the period of 2070–2100 with an increased temperature and a changed precipitation pattern consisting of reduced precipitation in summer and increased precipitation in spring and autumn. We subject five different land‐use types (two farming systems, three grasslands), differing in land‐use intensity, to ambient and future climatic conditions. The use of automated roofs and side panels to passively increase night temperatures results in an average increase in daily mean temperature by 0.55°C accompanied by a stronger increase in minimum temperatures (up to 1.14°C in average) with longer frost‐free periods and an increase in growing degree days by 5.2%. The combined use of mobile roofs and irrigation systems allows the reduction (in summer by ~20%) and increase in rainfall (in spring and autumn by ~10%) according to future scenarios superimposed on the ambient variation in precipitation. The large plot size and the technical configuration allow the establishment of realistic land‐use scenarios and long‐term observations of responses of ecosystem functions and community dynamics on relevant temporal and spatial scales. Thus, theGCEFprovides a well‐suited platform for the interdisciplinary research on the consequences of climate change under different land‐use scenarios.

Long‐term research in ecology and evolution: a survey of challenges and opportunities

AbstractLong‐term research in ecology and evolution (LTREE) is considered fundamental for understanding complex ecological and evolutionary dynamics. However, others have argued for revision of LTREE efforts given perceived limitations in current research priorities and approaches. Yet most arguments about the benefits and failings of LTREE could be argued to reflect the views of only the limited number of scientists who have authored reports on the field, and not the wider community of ecological and evolutionary scientists. To more systematically and quantitatively assess the views of the community on LTREE contributions and future activities, we conducted and here report the results of a survey of ecological and evolutionary scientists at primarily U.S.‐based institutions, completed by 1,179 respondents. The survey objectives were to (1) identify and prioritize research questions that are important to address through long‐term, ecological field experiments and (2) understand the role that these experiments might play in generating and applying ecological and evolutionary knowledge. Almost 80% (n = 936) of respondents said that long‐term experiments had contributed “a great deal” to ecological understanding. Compared to other research approaches (e.g., short‐term, single‐site, modeling, or lab), there was overwhelming support that multi‐site, long‐term research was very important for advancing theory, and that both observational and experimental approaches were required. Respondents identified a wide range of research questions for LTREE to address. The most common topic was the impact of global change (n = 1,352), likely because these processes play out over many years, requiring LTREE approaches to fully understand. Another recurrent theme was the potential of LTREE approaches to build evolutionary understanding across all levels of ecological organization. Critical obstacles preventing some scientists from engaging in LTREE included short‐term funding mechanisms and fewer publications, whereas the longer‐term value for advancing knowledge and an individual's career were widely recognized. Substantive advances in understanding ecological and evolutionary dynamics then seem likely to be made through engagement in long‐term observational and experimental research. However, wider engagement seems dependent on a more supportive research environment and funding structure, through increased institutional acknowledgment of the contributions of long‐term research, and greater program support during the establishment and maintenance of research.

Genetic diversity and kelp forest vulnerability to climatic stress

Genetic diversity confers adaptive capacity to populations under changing conditions but its role in mediating impacts of climate change remains unresolved for most ecosystems. This lack of knowledge is particularly acute for foundation species, where impacts may cascade throughout entire ecosystems. We combined population genetics with eco-physiological and ecological field experiments to explore relationships among latitudinal patterns in genetic diversity, physiology and resilience of a kelp ecosystem to climate stress. A subsequent ‘natural experiment’ illustrated the possible influence of latitudinal patterns of genetic diversity on ecosystem vulnerability to an extreme climatic perturbation (marine heatwave). There were strong relationships between physiological versatility, ecological resilience and genetic diversity of kelp forests across latitudes, and genetic diversity consistently outperformed other explanatory variables in contributing to the response of kelp forests to the marine heatwave. Population performance and vulnerability to a severe climatic event were thus strongly related to latitudinal patterns in genetic diversity, with the heatwave extirpating forests with low genetic diversity. Where foundation species control ecological structure and function, impacts of climatic stress can cascade through the ecosystem and, consequently, genetic diversity could contribute to ecosystem vulnerability to climate change.

Long-Term Research in Ecology and Evolution (LTREE): 2015 survey data.

To systematically assess views on contributions and future activities for long-term research in ecology and evolution (LTREE), we conducted and here provide data responses and associated metadata for a survey of ecological and evolutionary scientists. The survey objectives were to: (1) Identify and prioritize research questions that are important to address through long-term, ecological field experiments; and (2) understand the role that these experiments might play in generating and applying ecological and evolutionary knowledge. The survey was developed adhering to the standards of the American Association for Public Opinion Research. It was administered online using Qualtrics Survey Software. Survey creation was a multi-step process, with questions and format developed and then revised with, for example, input from an external advisory committee comprising senior and junior ecological and evolutionary researchers. The final questionnaire was released to ~100 colleagues to ensure functionality and then fielded 2 d later (January 7th , 2015). Two professional societies distributed it to their membership, including the Ecological Society of America, and it was posted to three list serves. The questionnaire was available through February 8th 2015 and completed by 1,179 respondents. The distribution approach targeted practicing ecologists and evolutionary biologists in the U.S. Quantitative (both ordinal and categorical) closed-ended questions used a predefined set of response categories, facilitating direct comparison across all respondents. Qualitative, open-ended questions, provided respondents the opportunity to develop their own answers. We employed quantitative questions to score views on the extent to which long-term experimental research has contributed to understanding in ecology and evolutionary biology; its role compared to other approaches (e.g., short-term experiments); justifications for and caveats to long-term experiments; and the relative importance of incentives for conducting long-term research. Qualitative questions were used to assess community views on the most important topics and questions for long-term research to address, and primary incentives and challenges to realizing this work. Finally, demographic data were collected to determine if views were conditional on such things as years of experience and field of expertise. The final questionnaire and all responses are provided for unrestricted use.

Field Experiments of Pollination Ecology: The Case of Lycoris sanguinea var. sanguinea.

Plant-pollinator interactions have been studied for approximately one hundred years. During that time, many field methods have been developed to clarify the pollination effectiveness of each pollinator for visited flowers. Pollinator observations have been one of the most common methods to identify pollinators, and bagging and cage experiments have been conducted to show the effectiveness of specific pollinators. In a previous study of Lycoris sanguinea var. sanguinea, its effective pollinators, the visitation frequencies of each floral visitor, and its reproductive strategies were not identified. This study reports the observation that small bees visited flowers that were partially opened (breaking buds). To the best of our knowledge, this phenomenon has not been reported previously. Further, this study investigates the hypothesis that small bees can pollinate at that flowering stage. This study demonstrates the basic methods of field experiments in pollination ecology using L. sanguinea var. sanguinea. Pollinator observations and digital video showed the visitation frequencies of each floral visitor. Bagging and cage experiments revealed that these flowers could be pollinated fully and that breaking-bud pollination could be important for the pollination of this plant species. The advantages and disadvantages of each method are discussed, and recent developments, including laboratory experiments, are described.

The genetics of chutes and ladders: a community genetics approach to tritrophic interactions

Community genetics research has firmly established that intraspecific genetic variation in single populations can have large extended ecological consequences for populations and entire communities of organisms. Here, we sought to understand the bottom‐up effects of plant genetic variation on herbivore preference and performance, and the top–down control of predators on herbivores and their joint effects on plant fitness and evolution. Following three ecological genetics field experiments we detected heritable variation in plant traits that influenced both the preference and performance of a specialist weevil on Oenothera biennis. However, the weevil's preference and performance were not genetically correlated among O. biennis plant genotypes. Although predators and parasitoids were abundant, predators had no detectable effect on weevil performance because high egg and larval mortality was caused by non‐predatory factors such as intraspecific competition. Finally, neither the specialist weevil nor predators influenced plant fitness. Our results suggest that the focal tritrophic community studied here is primarily shaped by the bottom–up effects of plant genetic variation on herbivores, while top–down effects have no clear impacts on O. biennis fitness or evolution. We suggest that future studies should incorporate plant intraspecific genetic variation as a fundamental part of tritrophic interactions including their eco‐evolutionary dynamics.

Temporal scale of field experiments in benthic ecology

Table S1. Summary of the 352 studies extracted from 293 publications from the Journal of Experimental Marine Biology and Ecology, Marine Ecology Progress Series, Ecology, Oecologia and Oikos over the period 1980 to 2013. Repetition of a reference indicates two separate studies were extracted from a single publication. Pulse experiments were defined as those receiving a one-off perturbation, generally of much shorter duration than the experiment itself. Press studies were defined as those receiving ongoing perturbations over the duration of the experiment. CE refers to controlled experimental studies; NE refers to natural experimental studies. Reference Habitat Press/ pulse Controlled/ natural experiment Experimental duration (mo) Sampling interval (mo)

Ecological genomics of mutualism decline in nitrogen-fixing bacteria.

Anthropogenic changes can influence mutualism evolution; however, the genomic regions underpinning mutualism that are most affected by environmental change are generally unknown, even in well-studied model mutualisms like the interaction between legumes and their nitrogen (N)-fixing rhizobia. Such genomic information can shed light on the agents and targets of selection maintaining cooperation in nature. We recently demonstrated that N-fertilization has caused an evolutionary decline in mutualistic partner quality in the rhizobia that form symbiosis with clover. Here, population genomic analyses of N-fertilized versus control rhizobium populations indicate that evolutionary differentiation at a key symbiosis gene region on the symbiotic plasmid (pSym) contributes to partner quality decline. Moreover, patterns of genetic variation at selected loci were consistent with recent positive selection within N-fertilized environments, suggesting that N-rich environments might select for less beneficial rhizobia. By studying the molecular population genomics of a natural bacterial population within a long-term ecological field experiment, we find that: (i) the N environment is indeed a potent selective force mediating mutualism evolution in this symbiosis, (ii) natural variation in rhizobium partner quality is mediated in part by key symbiosis genes on the symbiotic plasmid, and (iii) differentiation at selected genes occurred in the context of otherwise recombining genomes, resembling eukaryotic models of adaptation.

Ecological field experiment of short-term effects of fishing ban on fish assemblages in a tropical estuarine MPA

Marine Protected Areas (MPAs), in addition to their important role in the conservation of critical habitats and vulnerable species, are now also used in a context of ecosystem-based fisheries management. The aim of this study was to assess the observed changes in the fish population structure in the years following a fishing ban. The experiment took place in the Bamboung bolong, a small bay in the Sine Saloum estuary in Senegal, West Africa. The protection of this zone was undertaken with local fishermen support, and a formal MPA was created in 2004. The survey of the fish assemblages was initiated in 2003, the year before the fishing ban, and went on until 2007, with 12 sampling sites being monitored three times per year.In this paper, we describe and analyze the evolution of the fish assemblage during this five years' experimental period. Some changes have been highlighted on which the effect of the fishing ban was shown. After the fishing ban, an increase of total biomass and of maximal fish length has been registered. In the same time, the number of species has increased and the percentage of large and/or iconic species targeted by fishing has also increased. The community structure has been modified, with more small fish, more big fish (new large species and more large individuals in the original species) and fewer medium sized fish. The contribution of marine affinity species has increased in depend of the estuarine part of the assemblage. Finally, the trophic structure has been modified with an overall increase of the mean trophic level, resulting from an increase of the percentage of generalist or piscivorous predators and a sharp decrease of herbivorous and detritivorous low trophic level species. Marine predators which numbers and size were reduced by fisheries are again important components of the system. We argue that despite the intrinsic variability of the tropical estuarine environments, the introduction of a total ban on fishing in such estuarine zones can substantially improve the health status of the fish assemblage.

Ethical consideration in invasion ecology: A marine perspective

SummaryBiological introductions of species to regions outside their known natural distribution are considered a major threat to native marine biodiversity and a key consideration for ecological management. For most invasive species in marine systems, however, little is known about potential impacts. If we are to increase our knowledge of the processes and mechanisms behind the spread of nonindigenous species or determine economic or ecological impacts, manipulative ecological field experiments are the best way to unambiguously ascribe causal relationships. For studies of invasions, such research may result in species spread and the establishment of new viable populations. Is it ethical then, to take the risk of potentially modifying or endangering other species, populations or ecosystems? Is it possible to mitigate the risks? Or should invasion ecologists work under restrictions that limit their ability to fully assess the impact of invaders? Consideration of the ethics of experimentation is rarely carried out. As a consequence, we propose a decision model that includes possible risk of escape/establishment versus the value of the research to allow researchers and/or managers to critically evaluate what type of experimental approach is appropriate.

Beyond global change: lessons from 25 years of CO2 research

Over the past 25 years, countless experiments have been conducted on the impact of increased atmospheric CO2 concentration on various plants and ecosystems. While this research was motivated to better understand and predict how rising CO2 will affect the structure and function of ecosystems in the future, it also shed light on some general, CO2-research independent, aspects in ecological research. Interestingly, it is these general aspects that continue to create confusion and lead to misinterpretation. Here, we focus on seven interrelated key issues including (1) the confusion between fluxes and pools, (2) the stoichiometric aspects of growth and biomass production, (3) resource allocation within organisms, (4) data scaling and the choice of a reference metric, (5) the consideration of time and timing (experimental duration, ontogenetic shifts), (6) confounding and second-order (indirect or feedback) effects, and (7) the key role of biodiversity. The principles deriving from addressing these issues relate strongly to each other. Their concurrent consideration requires experimenters and modellers to likewise maintain a broad, holistic perspective. In this synthesis, we attempt to show how appropriate consideration of these principles can greatly enhance the assessment of the validity, plausibility and generality of experimental and modelling results. We conclude that neglecting to adequately address these key issues in ecological research may lead to overestimations of measured responses and/or simplistic interpretations. Our examples mostly originate from research on plant responses to elevated atmospheric CO2, but are also applicable to other areas of ecological research. We provide a checklist for the planning of ecological field experiments and the interpretation of their results that may help in avoiding common pitfalls.

Herbivores can select for mixed defensive strategies in plants

Resistance and tolerance are the most important defense mechanisms against herbivores. Initial theoretical studies considered both mechanisms functionally redundant, but more recent empirical studies suggest that these mechanisms may complement each other, favoring the presence of mixed defense patterns. However, the expectation of redundancy between tolerance and resistance remains unsupported. In this study, we tested this assumption following an ecological genetics field experiment in which the presence/absence of two herbivores (Lema daturaphila and Epitrix parvula) of Datura stramonium were manipulated. In each of three treatments, genotypic selection analyses were performed and selection patterns compared. Our results indicated that selection on resistance and tolerance was significantly different between the two folivores. Tolerance and resistance are not redundant defense strategies in D.stramonium but instead functioned as complementary defenses against both beetle species, favoring the evolution of a mixed defense strategy. Although each herbivore was selected for different defense strategies, the observed average tolerance and resistance were closer to the adaptive peak predicted against E.parvula and both beetles together. In our experimental population, natural selection imposed by herbivores can favor the evolution of mixed defense strategies in plants, accounting for the presence of intermediate levels of tolerance and resistance.

The influence of ecology on chimpanzee (Pan troglodytes) cultural behavior: A case study of five Ugandan chimpanzee communities.

The influence of ecology on the development of behavioral traditions in animals is controversial, particularly for chimpanzees (Pan troglodytes), for which it is difficult to rule out environmental influences as a cause of widely observed community-specific behavioral differences. Here, we investigated 3 potential scenarios that could explain the natural variation in a key extractive tool behavior, "fluid-dip," among several communities of chimpanzees of the Pan troglodytes schweinfurthii subspecies in Uganda. We compared data from previous behavioral ecological studies, field experiments, and long-term records of chimpanzee tool-using behavior. We focused on the quality of the available food, dietary preferences, and tool sets of 5 different communities, and carried out a standardized field experiment to test systematically for the presence of fluid-dip in 4 of these communities. Our results revealed major differences in habitat, available diet, and tool use behavior between geographically close communities. However, these differences in ecology and feeding behavior failed to explain the differences in tool use across communities. We conclude that ecological variables may lead both to innovation and loss of behavioral traditions, while contributing little to their transmission within the community. Instead, as soon as a behavioral tradition is established, sociocognitive factors likely play a key maintenance role as long as the ecological conditions do not change sufficiently for the tradition to be abandoned.

Variation: use it or misuse it–replication and its variants

Key Points in a previous article ([1][1]), we discussed variation between individuals, termed variance. When measurements are taken of subjects in separate groups, the variance of the measurements within the group can be compared with the variance that exists between groups. This allows us to

Phreatic groundwater ecosystems: research frontiers for freshwater ecology

Summary1. Phreatic ecosystems (saturated groundwater ecosystems in porous and fractured‐rock aquifers) are research frontiers for freshwater ecology. Many ecological issues that have been explored at length in surface‐water and hyporheic systems are unexplored in phreatic systems. Phreatic ecology is currently dominated by observational studies rather than experiments and focuses on pattern‐detection and description, rather than hypothesis‐testing and mechanistic explanations. These are characteristics of science disciplines in early developmental stages.2. Progress in phreatic ecology has been impeded by logistical problems including poor access, limited information about ecosystem boundaries and spatial heterogeneity, a lack of detailed habitat templates, limited taxonomic and biogeographic knowledge and the difficulties of field experiments. Each of these problems is assessed in this review, along with analytical techniques, instruments and concepts that may help researchers overcome them.3. Access to undisturbed phreatic systems is generally limited to narrow zones around wells. Limited access and sparse well arrays make detecting ecological patterns and relationships and delineating ecosystem boundaries difficult. Spatial resolution can be increased by installing wells in configurations suited to specific research topics; geostatistical methods are available for positioning new wells and optimising interpolation between them.4. Phreatic systems are characterised by multi‐scaled spatial and temporal heterogeneity. Lithofacies aggregations, buried fluvial bedforms, rock fractures and other geomorphic elements create structural and hydraulic heterogeneity, which lead in turn to spatial variation in solutes, biota and biogeochemical processes. The structural and hydraulic heterogeneity of study areas can be characterised and mapped with geophysical surveys and groundwater flow models. These models can help to identify flowpaths, recharge zones and aquifer boundaries and provide ecologically relevant hydrological variables.5. Physical habitat templates and classifications are needed to explain variation in phreatic populations and communities. A candidate classification system is proposed, based on environmental factors that govern the distribution and quality of groundwater habitats: climate, lithology, aquifer, confinement, recharge, hydrofacies and flowpath.6. Many phreatic species and higher‐level taxa remain undescribed, and the taxonomic resolution used in phreatic ecology studies is generally coarse. These problems impede progress in community ecology, biogeography and conservation biology. DNA barcoding and other molecular taxonomy methods are now being applied to groundwater fauna. Combining molecular taxonomy and traditional morphological methods could increase the accuracy and efficiency of species identification and help to define taxonomic boundaries.7. Field experiments and mensurative studies are rarely used in phreatic ecology, but they are needed to detect spatial and temporal patterns, quantify ecological relationships and test hypotheses and classification systems. Techniques from groundwater remediation and recharge studies can be adapted to ecological field experiments that utilise natural aquifer structures and groundwater flow dynamics.