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The relationship between an island’s size and the number of species on that island—the island species–area relationship (ISAR)—is one of the most well-known patterns in biogeography and forms the basis for understanding biodiversity loss in response to habitat loss and fragmentation. Nevertheless, there is contention about exactly how to estimate the ISAR and the influence of the three primary ecological mechanisms that drive it — random sampling, disproportionate effects, and heterogeneity. Key to this contention is that estimates of the ISAR are often confounded by sampling and estimates of measures (i.e., island-level species richness) that are not diagnostic of potential mechanisms. Here, we advocate a sampling-explicit approach for disentangling the possible ecological mechanisms underlying the ISAR using parameters derived from individual-based rarefaction curves estimated across spatial scales. If the parameters derived from rarefaction curves at each spatial scale show no relationship with island area, we cannot reject the hypothesis that ISARs result only from random sampling. However, if the derived metrics change with island area, we can reject random sampling as the only operating mechanism and infer that effects beyond sampling (i.e., disproportionate effects and/or heterogeneity) are also operating. Finally, if parameters indicative of within-island spatial variation in species composition (i.e., β-diversity) increase with island area, we can conclude that intra-island compositional heterogeneity plays a role in driving the ISAR. We illustrate this approach using representative case studies, including oceanic islands, natural island-like patches, and habitat fragments from formerly continuous habitat, illustrating several combinations of underlying mechanisms. This approach will offer insight into the role of sampling and other processes that underpin the ISAR, providing a more complete understanding of how, and some indication of why, patterns of biodiversity respond to gradients in island area.

BackgroundThis data paper provides a description of OpenNahele, the open Hawaiian forest plot database. OpenNahele includes 530 forest plots across the Hawaiian archipelago containing 43,590 individuals of 185 native and alien tree, shrub and tree fern species across six islands. We include estimates of maximum plant size (D950.1 and Dmax3) for 58 woody plant species, a key functional trait associated with dispersal distance and competition for light. OpenNahele can serve as a platform to test key ecological, evolutionary and conservation questions in a hotspot archipelago.New informationOpenNahele is the first database that compiles data from a large number of forest plots across the Hawaiian archipelago to allow broad and high resolution studies of biodiversity patterns.Keywords: Hawaii, forests, islands, biodiversity, community ecology, evolutionary ecology.

Climate and land‐use change are key drivers of global change. Full‐factorial field experiments in which both drivers are manipulated are essential to understand and predict their potentially interactive effects on the structure and functioning of grassland ecosystems. Here, we present 8 years of data on grassland dynamics from the Global Change Experimental Facility in Central Germany. On large experimental plots, temperature and seasonal patterns of precipitation are manipulated by superimposing regional climate model projections onto background climate variability. Climate manipulation is factorially crossed with agricultural land‐use scenarios, including intensively used meadows and extensively used (i.e., low‐intensity) meadows and pastures. Inter‐annual variation of background climate during our study years was high, including three of the driest years on record for our region. The effects of this temporal variability far exceeded the effects of the experimentally imposed climate change on plant species diversity and productivity, especially in the intensively used grasslands sown with only a few grass cultivars. These changes in productivity and diversity in response to alterations in climate were due to immigrant species replacing the target forage cultivars. This shift from forage cultivars to immigrant species may impose additional economic costs in terms of a decreasing forage value and the need for more frequent management measures. In contrast, the extensively used grasslands showed weaker responses to both experimentally manipulated future climate and inter‐annual climate variability, suggesting that these diverse grasslands are more resistant to climate change than intensively used, species‐poor grasslands. We therefore conclude that a lower management intensity of agricultural grasslands, associated with a higher plant diversity, can stabilize primary productivity under climate change. [ABSTRACT FROM AUTHOR]

Plant‐pollinator interactions are constrained by floral traits and available pollinators, both of which can vary across environmental gradients, with consequences for the stability of the interaction. Here, we quantified how the pollination ecology of a high‐mountain hummingbird‐pollinated plant changes across a progressively more stressful environmental gradient of the Venezuelan Andes. We compared pollination ecology between two populations of this plant: Piedras Blancas (PB) and Gavidia (GV), 4450 and 3600 m asl, respectively. We hypothesised that self‐compatibility might be higher at the higher altitude site, however we found that flowers showed similar capacities for self‐compatibility in both localities. Seed production by flowers exposed to natural pollinators was significantly higher in the lower locality, where we also found higher nectar quality, larger flowers and increased frequencies of pollinator visitations. Interestingly, the population energy offered in the nectar was the same for both localities due to the higher density and floral aggregation found in the higher altitude population. Our study demonstrates how two plant populations in different environmental conditions have different pollination ecology strategies. Pollinator visitations or their absence result in trait associations in one population that are independent in the other. These population differences are not explained by differences in pollinator assembly, but by environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Despite representing a fraction of the global terrestrial surface area, oceanic islands are disproportionately diverse in species, resulting from high rates of endemicity. Island plants are thought to share a unique phenotype—referred to as an island syndrome—which is thought to be driven by convergent evolution in response to selection by shared abiotic and biotic factors. One aspect of the island plant syndrome that has received relatively little research focus is that island plants are expected to have converged on conservative resource use associated with slow growth rates and weak competitive abilities. Here we tested whether native, woody Hawaiian plant species are phenotypically distinct—with more resource‐conservative leaf traits—compared to a globally distributed sample of continental species. Using an archipelago‐wide trait data set, we detected that on average, native Hawaiian species had lower leaf nutrient concentrations overall, and lower nutrient concentrations at high leaf mass per area, but no other phenotypic differences compared with continental plants. There was also considerable overlap in the trait spaces of native Hawaiian species and continental species. Our findings indicate that an island plant syndrome for leaf traits is not present in the Hawaiian flora, and that island species can demonstrate extensive variation in their resource‐use strategies, on a scale that is comparable with that of continental species worldwide. [ABSTRACT FROM AUTHOR]

Both means and year-to-year variances of climate variables such as temperature and precipitation are predicted to change. However, the potential impact of changing climatic variability on the fate of populations has been largely unexamined. We analyzed multiyear demographic data for 36 plant and animal species with a broad range of life histories and types of environment to ask how sensitive their long-term stochastic population growth rates are likely to be to changes in the means and standard deviations of vital rates (survival, reproduction, growth) in response to changing climate. We quantified responsiveness using elasticities of the long-term population growth rate predicted by stochastic projection matrix models. Short-lived species (insects and annual plants and algae) are predicted to be more strongly (and negatively) affected by increasing vital rate variability relative to longer-lived species (perennial plants, birds, ungulates). Taxonomic affiliation has little power to explain sensitivity to increasing variability once longevity has been taken into account. Our results highlight the potential vulnerability of short-lived species to an increasingly variable climate, but also suggest that problems associated with short-lived undesirable species (agricultural pests, disease vectors, invasive weedy plants) may be exacerbated in regions where climate variability decreases.

Human activities in mesic savanna ecosystems have resulted in plant communities that are heavily dominated by fire‐tolerant grass species, are less diverse, and offer fewer ecosystem services such as palatable plant biomass. Experimental studies manipulating fire and grass presence have mostly been conducted in ecosystems invaded by exotic grass species. However, these experiments are also relevant to ecosystems that have become dominated by native grass species due to changes in human activities. Our study compared three different management treatments in the Eastern Ghats of India, where mesic savanna ecosystems are highly dominated by the unpalatable native Cymbopogon grasses, specifically: (1) control (both Cymbopogon grasses and fire are present), (2) fire exclusion, and (3) manual removal of Cymbopogon grasses and fire exclusion. We found that both grass removal and fire exclusion were necessary to significantly increase palatable herbaceous plant biomass and species diversity, and that species diversity responses were only significant at larger spatial grains of investigation. High site‐to‐site variation in the grass removal and fire exclusion treatment prevented us from detecting significant differences in species composition across treatments, even though particular palatable grass species benefited from the treatment. Our study is in line with research from other mesic savanna systems showing that fire management alone is not sufficient to transition ecosystems to a desired or historical state. We demonstrate how normally costly management practices, such as manual removal of dominant grasses, can be reasonably achieved through collaboration between scientists, community governed village institutions, and government and nongovernment agencies in socioecological systems. [ABSTRACT FROM AUTHOR]