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Ecological responses to climate change may occur gradually with changing conditions, or they may occur rapidly once some threshold or \"tipping point\" has been reached. Here, we use a high-resolution, 30-year data set on the upper vertical limit of a high intertidal alga to demonstrate that distributional shifts in this species do not keep pace with gradual trends in air temperature or sea level, but rather occur in sudden, discrete steps. These steps occur when unusually warm air temperatures are associated with unusually calm seas and are contingent in the sense that neither atmospheric nor sea conditions by themselves were sufficient to generate the underlying physiological challenge. Shifts in the upper limit did not correlate with large environmental perturbations such as El Niños; rather, they appeared to be associated with stochastic departures from otherwise gradual environmental trends. Our results exemplify the view that multiple environmental factors should be considered when attempting to understand ecological responses to climate change. Furthermore, punctuated responses such as those we have identified urge caution when attempting to infer causal mechanisms and project future distributional shifts using data of limited temporal resolution or scope.

Environmental DNA (eDNA) detection has been shown to be an effective biosurveillance tool for freshwater fishes, but further research is needed to apply eDNA detection tools to small and rare fishes in large rivers. We developed an eDNA surveillance assay and protocol for monitoring the presence of the pygmy madtom (Noturus stanauli), a federally protected freshwater fish endemic to the Clinch and Duck rivers in Tennessee (United States, North America). Noturus stanauli is a diminutive fish that is exceedingly rare throughout its range; it is currently known only from a 115‐river‐km section of the Duck River and a 5‐river‐km section of the Clinch River. The aim of this research was to develop an eDNA assay to detect the presence of N. stanauli in both the Duck and Clinch rivers. We used this newly developed eDNA protocol to assess detection as a function of water depth and to further delineate the distribution of N. stanauli in both the Duck and Clinch rivers. Field sampling was performed to delineate the extent of N. stanauli's range in both rivers. Our results indicated that samples collected from three areas within the water column, as well as a sediment core samples, yielded equal detection rates. Our assay detected the presence of N. stanauli at a previously unknown site outside the current distribution in the Clinch River, located approximately 2.5‐river‐km downstream from the Tennessee‐Virginia state line. We demonstrated that eDNA detection is a promising tool for delineating the distribution of N. stanauli; however, further research is needed to assess environmental and life history variables that influence eDNA detection probability of small fish in large rivers. The federally endangered Pygmy Madtom (Noturus stanauli) is extremely rare and cryptic throughout its disjunct range in the Duck and Clinch Rivers in Tennessee, USA. Environmental DNA (eDNA) surveillance indicates that this species may have a wider distribution in the Clinch River than previous thought. Environmental variables, such as discharge, may influence eDNA detection and require further research.

Until recently, large apex consumers were ubiquitous across the globe and had been for millions of years. The loss of these animals may be humankind's most pervasive influence on nature. Although such losses are widely viewed as an ethical and aesthetic problem, recent research reveals extensive cascading effects of their disappearance in marine, terrestrial, and freshwater ecosystems worldwide. This empirical work supports long-standing theory about the role of top-down forcing in ecosystems but also highlights the unanticipated impacts of trophic cascades on processes as diverse as the dynamics of disease, wildfire, carbon sequestration, invasive species, and biogeochemical cycles. These findings emphasize the urgent need for interdisciplinary research to forecast the effects of trophic downgrading on process, function, and resilience in global ecosystems.

Detailed natural history coupled to experimental ecology has provided a rich harvest of insights into how natural communities in all ecosystems function, insights that cannot be gleaned from macroecological analyses. That detail, generated by small-spatial-scale but often lengthy experiments, is essential to managing and even restoring ecosystems. My essay focuses primarily on the ecology of exposed rocky intertidal shores, but I believe the derived implications are generalizable to all ecosystems. A mainly experimental approach has tended to avoid a preoccupation with niches but instead has focused on the ecological roles exercised by particular species. Attention to roles has produced a growing appreciation for trophic cascades and their consequences, with obvious implications for the management of fisheries and the conservation significance of apex predators. Some studies are more phenomenological and others more reductionist in focus, but all provide pathways toward understanding abundance and body size variation or a miscellany of indirect effects. Microecology in all ecosystems should continue to prosper independently of a macroecological, predominately terrestrial perspective.

The annual brown alga Postelsia palmaeformis is dependent for its survival on short-distance dispersal (SDD) where it is already established, as well as occasional long-distance colonization of novel sites. To quantify SDD, we transplanted Postelsia to sites lacking established plants within ≥10 m. The spatial distribution of the first naturally produced sporophyte generation was used to fit dispersal kernels in a hierarchical Bayesian framework. Mean dispersal distance within a year ranged from 0.16 to 0.50 m across sites; 95% of the recruits were within 0.38–1.32 m of the transplant. The fat-tailed exponential square root kernel was the best among the candidate models at describing offspring density and dispersal. Independent measurements of patch size over two to five generations permitted an evaluation of whether models parameterized by individual-level data could adequately predict longer-term persistence and spread at the patch scale. The observed spread rates generally fell within the 95% predictive intervals. Finally, Postelsia was eliminated from 14 occupied sites that were then followed for ≥27 yr. The probability of invasion when unoccupied declined and the probability of extinction when occupied increased with distance from the nearest propagule source. Sites >10 m from a source were rarely invaded, and one initially densely populated site isolated by 39 m has remained Postelsia-free since 1981. In spite of dispersal that is almost entirely within 2 m of the parent, the ability of our models to capture the observed dynamics of Postelsia indicates that short-range dispersal adequately explains the persistent and thriving Postelsia metapopulation on Tatoosh Island. However, the presence of Postelsia over a 2000-km coastal range with many gaps >1 km makes it clear that rare long-distance dispersal must be required to explain the geographic range of the species.

Seawater pH and the availability of carbonate ions are decreasing due to anthropogenic carbon dioxide emissions, posing challenges for calcifying marine species. Marine mussels are of particular concern given their role as foundation species worldwide. Here, we document shell growth and calcification patterns in Mytilus californianus, the California mussel, over millennial and decadal scales. By comparing shell thickness across the largest modern shells, the largest mussels collected in the 1960s–1970s and shells from two Native American midden sites (∼1000–2420 years BP), we found that modern shells are thinner overall, thinner per age category and thinner per unit length. Thus, the largest individuals of this species are calcifying less now than in the past. Comparisons of shell thickness in smaller individuals over the past 10–40 years, however, do not show significant shell thinning. Given our sampling strategy, these results are unlikely to simply reflect within-site variability or preservation effects. Review of environmental and biotic drivers known to affect shell calcification suggests declining ocean pH as a likely explanation for the observed shell thinning. Further future decreases in shell thickness could have significant negative impacts on M. californianus survival and, in turn, negatively impact the species-rich complex that occupies mussel beds.

In the low intertidal zone at Tatoosh Island, Washington, United States, minimal estimates of primary production can vary from 0 to an average of 86 kilograms of wet mass per square meter per year when the grazing assemblage is manipulated. Highly productive annual kelps (Laminariales) replace less productive perennial species when macroscopic grazers are reduced or absent, resulting in monodominant assemblages of Alaria marginata. Experiments were repeated in seven consecutive years. Increased species richness makes no significant additional contribution to annual production. Rather, a competitively superior species is favored when its enemies are reduced, suggesting that terrestrial perspectives on the role of biodiversity that are developed without considering consumers may not be general.

The southeastern United States is a global hotspot for crayfish biodiversity, with more than 300 described species in the region. Some of this diversity is unfortunately being threatened by anthropogenic activities and nearly one fifth of the North American crayfish species are currently threatened with extinction. Efforts to protect crayfish species have been hindered by a lack of information regarding their taxonomy, distribution, and conservation status. Here we target populations of the burrowing valley flame crayfish, Cambarus deweesae (Bouchard & Etnier 1979) for molecular taxonomy investigation. This species was originally known from the Clinch and Emory subdrainages in eastern Tennessee but it is currently listed as state endangered. The reporting of additional populations in Tennessee and Kentucky, however, has led to uncertainty about its conservation status. We analyzed sequence data from three mitochondrial genes (COI, 12S rRNA, and 16S rRNA) and from one nuclear gene (GAPDH) to decipher taxonomic questions regarding 15 crayfish populations, including 13 populations that are morphologically similar to C. deweesae (type locality sensu stricto). Combined analysis of all four genes demonstrated reciprocal monophyly for 14 out of 15 populations surveyed. Species delimitation methods, including GMYC and ABGD, identified between 11 and 13 new distinct genetic entities based on sequence divergence at the mitochondrial COI gene. Molecular results are combined with information on morphology and distribution in order to resolve taxonomic uncertainties within C. deweesae and its close relatives. The study highlights the need for fine-scale investigations into the phylogeography of North American burrowing crayfishes.

In any community, a keystone species is one that has an effect that is disproportionate to its abundance. A species that acts as a keystone predator consumes the competitively dominant species, leading to an overall increase in local species diversity. The earliest and still one of the best examples of such a predator is the ochre seastar (Pisaster ochraceus). Along western North America's rocky shorelines from Alaska to Baja (Figure 1), Pisaster's appetite for the California mussel (Mytilus californianus) is well documented. Foundational experiments on Makah Tribal Lands in Washington State by one of us (RTP) in the 1960s showed that when Pisaster was intentionally excluded from a rocky intertidal slope, the mussel population advanced toward the lower reaches of the intertidal zone and competitively eliminated a rich diversity of other species (Paine 1966, 1974).