Gradient and scale are two key concepts in ecology and evolution that are closely related but inherently distinct. While scale commonly refers to the dimensional space of a specific ecological/evolutionary (eco–evo) issue, gradient measures the range of a given variable. Gradient and scale can jointly and interactively influence eco–evo patterns. Extensive previous research investigated how changing scales may affect the observation and interpretation of eco–evo patterns; however, relatively little attention has been paid to the role of changing gradients. Here, synthesizing recent research progress, we suggest that the role of scale in the emergence of ecological patterns should be evaluated in conjunction with considering the underlying environmental gradients. This is important because, in most studies, the range of the gradient is often part of its full potential range. The difference between sampled (partial) versus potential (full) environmental gradients may profoundly impact observed eco–evo patterns and alter scale–gradient relationships. Based on observations from both field and experimental studies, we illustrate the underlying features of gradients and how they may affect observed patterns, along with the linkages of these features to scales. Since sampled gradients often do not cover their full potential ranges, we discuss how the breadth and the starting and ending positions of key gradients may affect research design and data interpretation. We then outline potential approaches and related perspectives to better integrate gradient with scale in future studies.
1. At global scales, species richness is declining. However, at local scales, understanding exactly how, where and why biodiversity is changing becomes challenging since researchers have assessed biodiversity trends using different indicators, data sources and methods (e.g. repeated measurements at the same site over time vs. space-for-time substitutions).2. In this study, we present a multifaceted analysis of biodiversity change by assessing how tree diversity in Québec, Canada changed between two sampling periods (1970-1977 and 2005-2016), in regards to different: levels of diversity (alpha diversity, temporal turnover and spatial beta diversity), dimensions of diversity (taxonomic, functional and phylogenetic), metrics of diversity (presenceabsence and abundance based), and spatial scales of analysis (plot, 50, 100 and 200 km). We then assess how well potential drivers of biodiversity change (climate change and land cover change) explain the observed changes in alpha diversity. Since the data came from plots that remained forested over the course of the study, we used historical land cover change data and scenario analyses to test whether results from forest plots were likely to be representative of the broader landscape.3. Across all levels, dimensions, metrics and spatial scales of analysis, we found either increases or no net change in diversity over time, with wide distributions of values around the mean. Presence-absence metrics often indicated increases in diversity over time, while abundance-based metrics were more likely to show no net change. Potential drivers such as climate change and land cover change explained only a small fraction of the variation in alpha diversity change (i.e. why particular sites experienced positive vs. negative change) at the plot scale (adjusted R 2 ≈ 0.03), but a greater fraction at coarser spatial scales (adjusted R 2 of ~0.10 to ~0.50). Results from these forest plots are likely representative of the diversity change within the study region, since estimates of alpha diversity change only became negative under scenarios with the most extreme disturbance impacts.4. Synthesis. None of our indicators showed evidence of declines in alpha or beta diversity of trees in temperate and boreal forests in Quebec (except for simulations with extremely high forest loss), but we did find temporal turnover in
In 2006, Walker et al. published an article titled, "A Handful of Heuristics and Some Propositions for Understanding Resilience in Social-ecological Systems." The article was incorporated into the Ecology and Society special feature, Exploring Resilience in Social-Ecological Systems. Walker et al. identified five heuristics and posed 14 propositions for understanding resilience in social-ecological systems. At the time, the authors hoped the paper would promote experimentation, critique, and application of these ideas in resilience and social-ecological systems research. To determine the extent to which these propositions have achieved the authors' hopes, we reviewed the scientific literature on socialecological systems since the article was published. Using Scopus, we identified 627 articles that cited the Walker et al. article. We then identified and assessed the articles relative to each proposition. In addition, we conducted a more general Scopus review for articles that did not cite the Walker et al. article specifically but incorporated a proposition's concepts. Overall, articles often cite Walker et al. as a reference for a definition of a heuristic or ecological resilience generally and not to reference a specific proposition. Nonetheless, every proposition was at least mentioned in the literature and used to advance resilience scholarship on social-ecological systems. Eleven propositions were tested by multiple articles through application of case studies or other research, and 7 of the 11 propositions were substantially discussed and advanced. Finally, three propositions were heavily critiqued either as concepts in resilience literature or in their application.
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