The spatial and temporal domains of modern ecology

Articles https://doi.org/10.1038/s41559-018-0524-4 The spatial and temporal domains of modern ecology Lyndon Estes 1,2*, Paul R. Elsen 3,4, Timothy Treuer4, Labeeb Ahmed5, Kelly Caylor6,7, Jason Chang5, Jonathan J. Choi4 and Erle C. Ellis 5 To understand ecological phenomena, it is necessary to observe their behaviour across multiple spatial and temporal scales. Since this need was first highlighted in the 1980s, technology has opened previously inaccessible scales to observation. To help to determine whether there have been corresponding changes in the scales observed by modern ecologists, we analysed the resolution, extent, interval and duration of observations (excluding experiments) in 348 studies that have been published between 2004 and 2014. We found that observational scales were generally narrow, because ecologists still primarily use conventional field techniques. In the spatial domain, most observations had resolutions ≤1 m2 and extents ≤10,000 ha. In the temporal domain, most observations were either unreplicated or infrequently repeated (>1 month interval) and ≤1 year in duration. Compared with studies conducted before 2004, observational durations and resolutions appear largely unchanged, but intervals have become finer and extents larger. We also found a large gulf between the scales at which phenomena are actually observed and the scales those observations ostensibly represent, raising concerns about observational comprehensiveness. Furthermore, most studies did not clearly report scale, suggesting that it remains a minor concern. Ecologists can better understand the scales represented by observations by incorporating autocorrelation measures, while journals can promote attentiveness to scale by implementing scale-reporting standards. T he scales at which ecosystems are observed play a critical role in shaping our understanding of their structure and function1–3. Ecological patterns emerge from temporal and spatial domains that may be coarser or finer than the processes that shape them, which means that investigation across multiple scales is essential for understanding ecological phenomena1,4. This awareness has grown rapidly since the 1980s5, accelerated by the need to understand how changes in the global climate, ocean and land systems are affecting everything from individual populations6 to entire biomes7, while technological advances in areas such as remote sensing and genetics are making it ever-easier to quantify ecological features across a broad and increasing range of scales2,5. Given the growing awareness of scale, expanding data-gathering capabilities and the fact that the most comprehensive (and arguably best-known) meta-analyses8,9 of ecological research scales were published nearly 30 years ago (but see refs 4,10 for more recent reviews), it is both timely and important to assess the scales of contemporary ecological investigation. To address this need, we quantified the spatial and temporal domains of empirical observations that were reported within recently (2004–2014) published ecological studies. We define domain as the distribution of observations within the spectrum of one or more scale dimensions (note: this definition differs from the ‘domain of scale’3, which is 'a portion of the scale spectrum within which process–pattern relationships are consistent regardless of scale’), and empirical observations as ecological observations collected under uncontrolled or non-manipulated conditions. Empirical observations are critical for developing and testing the models that explain why ecological patterns vary in time and space1,8; therefore, the spatio-temporal domains of observations provide an important indicator of the field’s progress towards achieving a holistic, predictive understanding of ecosystems1,2. Our study focused on two dimensions of spatial scale (that is, resolution (grain) and extent) and two of temporal scale (that is, interval and duration) (Table 1). We analysed the observational domains within each of these four dimensions and between pairs of these dimensions. We also assessed two additional dimensions—actual extent (the summed area of spatial replicates) and actual duration (the summed observational time of temporal replicates)—which we used to evaluate how much the actual scales of observation (that is, how much space and time are covered by the measurement) differ from the scales they ostensibly represent. These differences may impact how effectively observations characterize ecological phenomena. For one, an increasing gap between actual and ostensible observational scales implies greater interpolation or extrapolation of observed measurements, raising the odds of over-leveraging data. Furthermore, since natural systems are frequently complex, nonlinear and non-random11–13, a larger gap increases the likelihood of data challenges such as censoring (sensu14) as phenomena may resolve themselves in the space or time between replicates. Results We reviewed 348 papers randomly selected from 42,918 published between 2004 and 2014 in the top 30 ecology-themed journals. We extracted scale data from 378 observations of ‘natural’ (that is, nonexperimentally manipulated) ecological features reported within 133 of the reviewed papers (plus an additional 62 cited as the source of observations). Most sampled observations were collected using conventional field methods (80%), followed by automated in situ Graduate School of Geography, Clark University, Worcester, MA, USA. 2Woodrow Wilson School, Princeton University, Princeton, NJ, USA. Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, USA. 4Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA. 5Department of Geography and Environmental Systems, University of Maryland, Baltimore County, Baltimore, MD, USA. 6Department of Geography, University of California, Santa Barbara, Santa Barbara, CA, USA. 7Bren School of Environmental Science and Management, University of California, Santa Barbara, Santa Barbara, CA, USA. *e-mail: 1 3 Nature Ecology & Evolution | VOL 2 | MAY 2018 | 819–826 | www.nature.com/natecolevol © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. 819 Articles Nature Ecology & Evolution Table 1 | Scale dimensions of ecological observations assessed in this meta-analysis Component Spatial Temporal Units Description Resolution m2 Area of an individual spatial replicate (for example, plot) Extent ha Area encompassed by all spatial replicates Actual extent ha Summed area of all spatial replicates Interval days Time elapsed between successive temporal replicates Duration days Time elapsed between first and last temporal replicates Actual duration days Summed observational time of all temporal replicates sensing techniques (12.4%), remote sensing (6.9%) and palaeoreconstruction (<0.8%). Observational domains wi (...truncated)