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1. Increasingly, ecologists conceptualize local communities as connected to a regional species pool rather than as isolated entities. By this paradigm, community structure is determined through the relative strengths of dispersal-driven regional effects and local environmental factors. However, despite explicit incorporation of dispersal, metacommunity models and frameworks often fail to capture the realities of natural systems by not accounting for the configuration of space within which organisms disperse. This shortcoming may be of particular consequence in riverine networks which consist of linearly -arranged, hierarchical, branching habitat elements. Our goal was to understand how constraints of network connectivity in riverine systems change the relative importance of local vs. regional factors in structuring communities. 2. We hypothesized that communities in more isolated headwaters of riverine networks would be structured by local forces, while mainstem sections would be structured by both local and regional processes. We examined these hypotheses using a spatially explicit regional analysis of riverine macroinvertebrate communities, focusing on change in community similarity with distance between local communities [i.e., distance-decay relationships; (DDRs)], and the change in environmental similarity with distance. Strong DDRs frequently indicate dispersal-driven dynamics. 3. There was no evidence of a DDR in headwater communities, supporting our hypothesis that dispersal is a weak structuring force. Furthermore, a positive relationship between community similarity and environmental similarity supported dynamics driven by local environmental factors (i.e., species sorting). In mainstem habitats, significant DDRs and community x environment similarity relationships suggested both dispersal-driven and environmental constraints on local community structure (i.e., mass effects). 4. We used species traits to compare communities characterized by low vs. high dispersal taxa. In headwaters, neither strength nor mode (in-network vs. out of network) of dispersal changed our results. However, outcomes in mainstems changed substantially with both dispersal mode and strength, further supporting the hypothesis that regional forces drive community dynamics in mainstems. 5. Our findings demonstrate that the balance of local and regional effects changes depending on location within riverine network with local (environmental) factors dictating community structure in headwaters, and regional (dispersal driven) forces dominating in mainstems.

1. Understanding the processes by which species sort themselves into communities remains a central puzzle for attempts to maintain biodiversity. It remains unclear whether any single assembly process is generally dominant or whether the influence of contrasting processes varies in a predictable way relative to biotic and abiotic gradients. Abundance-weighted niche overlap between species provides a powerful means of contrasting two major assembly processes - niche complementarity and environmental filtering. 2. We examined mean overlap for four vegetative functional traits, relative to that expected when abundances were randomly allocated to species co-occurring in experimental plots in a wet meadow. This provided a test of whether any single assembly process prevailed for the meadow as a whole and across all traits. The effects of mowing, fertilization and dominant species removal, and associated gradients of Simpson's dominance and biomass on the niche overlap of plots, were also examined. 3. Niche overlap was higher than expected at random for three of the four traits studied (height, leaf and stem dry matter content, leaf C:N ratio). However, niche overlap was lower than expected for specific leaf area. 4. Mowing was the treatment with the greatest effect on both niche overlap and biomass, with overlap significantly lower in the absence of mowing for three of the traits, while biomass was lower in mown plots. For three of the traits there was evidence of a significant decrease in overlap with increasing biomass, but not increasing dominance. None of the significant mowing effects on overlap remained when the effect of biomass had been removed. 5. Synthesis: These results suggest that the importance of niche differences between species in structuring grassland communities should increase with increasing biomass and decrease with disturbance in grassland communities. They also emphasize that contrasting community assembly processes may occur for different niche axes, even within a single community.

Many marine ecosystems have undergone ‘regime shifts’, i.e. abrupt reorganizations across trophic levels. Establishing whether these constitute shifts between alternative stable states is of key importance for the prospects of ecosystem recovery and for management. We show how mechanisms underlying alternative stable states caused by predator–prey interactions can be revealed in field data, using analyses guided by theory on size-structured community dynamics. This is done by combining data on individual performance (such as growth and fecundity) with information on population size and prey availability. We use Atlantic cod (Gadus morhua) and their prey in the Baltic Sea as an example to discuss and distinguish two types of mechanisms, ‘cultivation-depensation’ and ‘overcompensation’, that can cause alternative stable states preventing the recovery of overexploited piscivorous fish populations. Importantly, the type of mechanism can be inferred already from changes in the predators' body growth in different life stages. Our approach can thus be readily applied to monitored stocks of piscivorous fish species, for which this information often can be assembled. Using this tool can help resolve the causes of catastrophic collapses in marine predatory–prey systems and guide fisheries managers on how to successfully restore collapsed piscivorous fish stocks.

1. Fire is an integral process in savannas because it plays a crucial role in altering woody cover of this globally important biome. 2. In this study, we examine the long-term effects of varying fire frequencies over a 60-year time period in South Africa. We analyse the effects of fire exclusion and of experimental burns every 1, 2 and 3 years on woody cover, tree abundance and stem structure on a wet and dry savanna. 3. Increased fire frequency did not display a consistent effect on woody cover. The presence of fire, irrespective of frequency, was much more influential in lowering tree abundance in the wet savanna than the dry savanna. In the dry savanna, fire was more effective in greatly increasing coppicing in trees, when compared to the wet savannas. 4. Synthesis. The effects of fire on three measures of savanna woody vegetation differed between wet and dry experimental sites. We suggest that vegetation responses to fire are dependent on local conditions, which are likely influenced by rainfall. Therefore, we suggest that management strategies should take account of whether a savanna is a wet or dry system when implementing fire management regimes.

The frequency and duration of marine heat waves (MHWs) have recently increased. There is therefore an urgent need to understand the response of marine organisms to MHWs. However, most estimates of MHW impacts on abundances include the effects of environmental stochasticity other than the MHWs. In addition, although MHWs sometimes persist for year-round or occur repeatedly for shorter periods, the accumulative carryover effects (ACEs)— the effects of sequential events accumulating additively over time— of MHWs on organisms have never been evaluated. Furthermore, the relationship between species niche traits other than thermal niches and susceptibility to MHWs is unknown. We examined the impacts of MHWs in southeastern Hokkaido, northern Japan, in summer from 2010 to 2016 on rocky intertidal communities by distinguishing MHW effects from environmental stochasticity. We asked (1) Did MHWs have ACEs on four major functional groups: macroalgae, sessile invertebrates, herbivorous invertebrates, and carnivorous invertebrates? (2) Does ignoring ACEs lead to biased assessments? (3) How did the effects of the MHWs on functional groups and their subsequent recovery differ? And (4) How does the susceptibility to MHWs differ with species niche (thermal and vertical) traits? We detected ACEs of MHWs and found that if they are ignored, the effects of MHWs can be underestimated. Although MHWs are known to reduce the abundance of macroalgae and increase that of sessile invertebrates in rocky intertidal habitats, our results show that macroalgal abundance increased during and after MHWs, whereas sessile invertebrates showed no change during or after MHWs. The abundance of herbivorous mollusks decreased during and after MHWs. Carnivorous invertebrates declined during MHWs and in the first year after MHWs. During and after MHWs, abundances of species with low thermal niches decreased and those with high thermal niches increased. There were no differences in response to MHWs between vertical niches when accumulative carryover effects were ignored. These results emphasize the importance of considering ACEs when assessing the response of marine organisms to MHWs, and that more studies of these responses are needed for a variety of ecosystems, regions and organisms to predict the responses of marine organisms.

Summary 1. Worldwide, the floristic composition of temperate forests bears the imprint of past land use for decades to centuries as forests regrow on agricultural land. Many species, however, display significant interregional variation in their ability to (re)colonize post‐agricultural forests. This variation in colonization across regions and the underlying factors remain largely unexplored. 2. We compiled data on 90 species and 812 species × study combinations from 18 studies across Europe that determined species’ distribution patterns in ancient (i.e. continuously forested since the first available land use maps) and post‐agricultural forests. The recovery rate (RR) of species in each landscape was quantified as the log‐response ratio of the percentage occurrence in post‐agricultural over ancient forest and related to the species‐specific life‐history traits and local (soil characteristics and light availability) and regional factors (landscape properties as habitat availability, time available for colonization, and climate). 3. For the herb species, we demonstrate a strong (interactive) effect of species’ life‐history traits and forest habitat availability on the RR of post‐agricultural forest. In graminoids, however, none of the investigated variables were significantly related to the RR. 4. The better colonizing species that mainly belonged to the short‐lived herbs group showed the largest interregional variability. Their recovery significantly increased with the amount of forest habitat within the landscape, whereas, surprisingly, the time available for colonization, climate, soil characteristics and light availability had no effect. 5. Synthesis. By analysing 18 independent studies across Europe, we clearly showed for the first time on a continental scale that the recovery of short‐lived forest herbs increased with the forest habitat availability in the landscape. Small perennial forest herbs, however, were generally unsuccessful in colonizing post‐agricultural forest – even in relatively densely forested landscapes. Hence, our results stress the need to avoid ancient forest clearance to preserve the typical woodland flora.

The Cerrado has a wide diversity of fauna and flora, and the knowledge of its horizontal structure, in different time intervals allows the prediction of its structural and floristic characteristics. The aim of this study was to evaluate the changes in structure and composition of tree community in three fragments of Cerrado with low anthropization, in an interval of 11 years at Minas Gerais state. Rectangular plots of fixed size were sampled, measuring stem diameter and height of all living arboreal individuals with diameter at 1.30 meters above ground (DBH) ≥ 5 cm. The tree vegetation dynamics study of the areas was performed, as well as the floristic analysis and the diametric structure. Considering all fragments and years of measurement, the recruitment of trees surpassed its mortality. The basal area varied between 3.67 and 13.07 m².ha-1. The studied areas, considering all fragments and years of measurement, showed a Shannon diversity index (H') from 3.43 to 3.87 nat.ind-1 and Pielou equitability index (J') ranged an interval between 0.77 and 0.82. The similarity calculated by the Jaccard index (J), when performed per plot considering the three fragments, showed a value of 0.2653. Also, related to the development and growth of the study areas, it can be inferred that all fragments and their respective years of measurement had a J-inverse pattern. In conclusion, it can be inferred that the three fragments maintained a representative growth in number of individuals and basal area.

Grid-based inventories of 1,924 deciduous forests plots in Germany and 4,775 in Romania were used to investigate tree species composition as affected by browsing and grazing under different forest management (rotation forestry, selectively cut forest, protected forest). At regional scale, the loss of tree species in the dominant layer was between 52 to 67% in Germany and of 10 to 30% in Romania, with largest effects in protected nature reserves in Germany. At plot level, only 50% (Germany) to 54% (Romania) of canopy species were found in the regeneration layer with a height of 1.5 m. Browsing was influenced by the proportion of Fagus in the regenerating trees in Germany, and by stand density, basal area, and management in both regions. Structural equation modeling explained 11 to 26% of the variance in species loss based on the fresh loss of the terminal bud in the winter prior to the inventory work (one season browsing). Browsing (and grazing in Romania) is shown to be a significant cause of species loss across both countries and all management types. Potential cascading effects on other organisms of deciduous forest ecosystems are discussed. We conclude that the present hunting practices that support overabundant ungulate populations constitute a major threat to the biodiversity of deciduous forests in Germany and Romania and to other places with similar ungulate management, and that changes my only be possible by modernizing the legal framework of hunting.

1. Variation in forest gap size and duration are a result of spatial contiguity and continuity of gap infilling and tree mortality over time, which influences both species recruitment and successional pathways. 2. As many gaps in boreal forests are small, their size and duration will affect the conditions influencing species recruitment. We investigate the spatial dynamics of these gaps (i.e. those which are persistent, ephemeral, expanding, displaced or disappearing) and tested whether gap spatio-temporal patterns are consistent over different temporal periods (1998—2003 and 2003—2007). 3. Forest canopy gaps were reconstructed for three plots (10, 10 and 6 ha in size) in southern boreal mixedwood forests around Lake Duparquet, north-western Quebec (Canada), using a time series of high-resolution canopy surface profiles from three light and ranging detection (lidar) system surveys during a 9-year window. High-resolution images were used to individually identify early and late successional gap makers. Dynamic changes in canopy gaps over a 9-year period were investigated by implementing concepts of random set theory within a temporal GIS framework. Mortality was higher on the gap edges than in the forest interior, and shade tolerant species were more likely to be gap makers than shade intolerant species. Edge trees that died causing the expansion of gaps were much smaller than trees creating new gaps. Although the overall gap size distribution was consistent over the 9 years studied, the proportion of the total area opening and closing varied between periods. Independent analyses of time windows show an abundance of small gaps (below 40 cm²) appearing and disappearing; however, analysis of spatial contiguity shows that the majority (over 80%) of gaps of all sizes were displaced and/or expanded. 4. Synthesis. Contrary to the previous perception that small gaps are ephemeral, which would favour the recruitment of late successional species, our findings indicate that gap displacement and expansion may be a mechanism explaining the maintenance of favourable conditions for the recruitment of shade intolerant individuals, which has been previously observed in high-latitude old-growth boreal forests.

Understanding the mechanisms governing coexistence is a central goal in ecology and has implications for conserving and restoring communities, yet the high diversity in many plant communities is difficult to explain. Theory suggests that plant–soil feedbacks (PSF) can lead to frequency‐dependent coexistence by suppressing conspecifics more than heterospecifics, potentially helping to explain high‐diversity plant communities. In addition, species‐specific population dynamics, including the rate at which individuals are replaced in a population or population turnover rate, may influence coexistence outcomes. We have created a rigorous test of the coexistence predictions of theory by generating a soil heterogeneity experiment in the field and testing for mutual invasibility by establishing resident populations, then experimentally invading them. Experimental tests of mutual invasibility can demonstrate coexistence because, if species are able to invade one another's populations when at low density, they should exhibit long‐term coexistence. We use pairs of congeners in this experiment that coexist at small spatial scales, sometimes within cm, at our field site. We demonstrate that invader individuals established better in congener's soils than in conspecific soils, consistent with plant–soil feedback mediated coexistence. This effect was often mediated by competition with established resident plants. Further, we show that soil heterogeneity interacted with the population turnover rate of the resident population to influence invasibility (P < 0.10), consistent with the theoretical prediction that a plant's population dynamics will interact with heterogeneity to influence coexistence. Synthesis. Plant–soil feedbacks (PSF) can in theory lead to frequency‐dependent coexistence, and reciprocally, negative feedback effects in glasshouse experiments are often consistent with this prediction. We provide the first field test of mutual invasibility structured by PSF, demonstrating that PSF can lead to coexistence when they create a patchy, or heterogeneous, soil environment. This work suggests that understanding the influence of PSF on diversity necessitates understanding the spatial scale at which soil heterogeneity emerges in the field. Thus, high diversity might be maintained in plant communities by heterogeneity created by plants' influence on the soil, and this outcome depends strongly on population dynamics.