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USGS · 70056499

Ecological role and services of tropical mangrove ecosystems: a reassessment

Abstract

Aim To reassess the capacity of mangroves for ecosystem services in the light of recent data. Location Global mangrove ecosystems. Methods We review four long-standing roles of mangroves: (1) carbon dynamics – export or sink; (2) nursery role; (3) shoreline protection; (4) land-building capacity. The origins of pertinent hypotheses, current understanding and gaps in our knowledge are highlighted with reference to biogeographic, geographic and socio-economic influences. Results The role of mangroves as C sinks needs to be evaluated for a wide range of biogeographic regions and forest conditions. Mangrove C assimilation may be under-estimated because of flawed methodology and scanty data on key components of C dynamics. Peri-urban mangroves may be manipulated to provide local offsets for C emission. The nursery function of mangroves is not ubiquitous but varies with spatio-temporal accessibility. Connectivity and complementarity of mangroves and adjacent habitats enhance their nursery function through trophic relay and ontogenetic migrations. The effectiveness of mangroves for coastal protection depends on factors at landscape/geomorphic to community scales and local/species scales. Shifts in species due to climate change, forest degradation and loss of habitat connectivity may reduce the protective capacity of mangroves. Early views of mangroves as land builders (especially lateral expansion) were questionable. Evidence now indicates that mangroves, once established, directly influence vertical land development by enhancing sedimentation and/or by direct organic contributions to soil volume (peat formation) in some settings. Main conclusions Knowledge of thresholds, spatio-temporal scaling and variability due to geographic, biogeographic and socio-economic settings will improve the management of mangrove ecosystem services. Many drivers respond to global trends in climate change and local changes such as urbanization. While mangroves have traditionally been managed for subsistence, future governance models must involve partnerships between local custodians of mangroves and offsite beneficiaries of the services.

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BibTeXRIS

Shing Yip Lee, Jurgene H. Primavera, Farid Dahdouh-Guebas, Karen McKee, Jared O. Bosire, Stefano Cannicci, Karen Diele, Francois Fromard, Nico Koedam, Cyril Marchand, Irving Mendelssohn, Nibedita Mukherjee, Sydne Record. 2014-03-06. Ecological role and services of tropical mangrove ecosystems: a reassessment. https://doi.org/10.1111/geb.12155

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Local and landscape-level environmental conditions drive habitat selection across terrestrial mammal species

Aim Animal movements are a fundamental process affecting communities and ecosystems. Quantifying habitat selection across species and habitats is key for understanding how animals respond to environmental change. Currently, we lack comparative studies that examine how habitat selection varies across species traits and landscapes. We aim to quantify global patterns of habitat selection to help understand the fundamental drivers of movement behaviour. Location Global. Time Period Contemporary. Major Taxa Studied Terrestrial mammals. Methods We estimated selection coefficients for terrain ruggedness, vegetation productivity, human population density and distance to roads of individual terrestrial mammals through step-selection analysis of 1344 GPS tracks across 48 species. We quantified intra- and interspecific variation and tested whether selection coefficients were associated with species traits and habitat availability. Results We observe an overall avoidance of roads and areas of high human population density as well as rugged terrain, with a large proportion of individuals selecting for areas of intermediate NDVI. However, we also found large intraspecific variation in habitat selection and show that this variation is predicted by local and landscape-level environmental conditions rather than species traits. Individuals in more remote areas exhibited weaker functional responses to human presence than those in more disturbed areas. Avoidance of rugged terrain is also context-dependent, with stronger avoidance when local ruggedness is high. The only exception to the observed intraspecific variability is consistent species-level responses to road proximity. Main Conclusions Our findings contribute to the understanding of habitat selection by terrestrial mammals, showing that selection is largely shaped by environmental conditions and that animals exhibit high plasticity in their responses. Our results also provide further evidence for the significant impact of roads on animal movement. These insights can help us to understand the potential effects of environmental change on the behaviour of mammal species around the world.

Global Ecology and Biogeography

A quantitative classification of the geography of non-native flora in the United States

Aim Non-native plants have the potential to harm ecosystems. Harm is classically related to their distribution and abundance, but this geographical information is often unknown. Here, we assess geographical commonness as a potential indicator of invasive status for non-native flora in the United States. Geographical commonness could inform invasion risk assessments across species and ecoregions. Location Conterminous United States. Time Period Through 2022. Major Taxa Studied Plants. Methods We compiled and standardised occurrence and abundance data from 14 spatial datasets and used this information to categorise non-native species as uncommon or common based on three dimensions of commonness: area of occupancy, habitat breadth and local abundance. To assess consistency in existing categorizations, we compared commonness to invasive status in the United States. We identified species with higher-than-expected abundance relative to their occupancy, habitat breadth or residence time. We calculated non-native plant richness within United States ecoregions and estimated unreported species based on rarefaction/extrapolation curves. Results This comprehensive database identified 1874 non-native plant species recorded in 4,844,963 locations. Of these, 1221 species were locally abundant (> 10% cover) in 797,759 unique locations. One thousand one hundred one non-native species (59%) achieved at least one dimension of commonness, including 565 species that achieved all three. Species with longer residence times tended to meet more dimensions of commonness. We identified 132 species with higher-than-expected abundance. Ecoregions in the central United States have the largest estimated numbers of unreported, abundant non-native plants. Main Conclusions A high proportion of non-native species have become common in the United States. However, existing categorizations of invasive species are not always consistent with species' abundance and distribution, even after considering residence time. Considering geographical commonness and higher-than-expected abundance revealed in this new dataset could support more consistent and proactive identification of invasive plants and lead to more efficient management practices.

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Using plant invasions to compare occurrence- and abundance-based calculations of biotic homogenisation: Are results complementary or contradictory?

Aim Beta diversity quantifies the similarity of ecological assemblages. Its increase, known as biotic homogenisation, can be a consequence of biological invasions. However, species occurrence (presence/absence) and abundance-based analyses can produce contradictory assessments of the magnitude and direction of changes in beta diversity. Previous work indicates these contradictions should be less frequent in nature than in theory, but a growing number of empirical studies report discrepancies between occurrence- and abundance-based approaches. Understanding if these discrepancies represent a few isolated cases or are systematic across a diversity of ecosystems would allow us to better understand the general patterns, mechanisms and impacts of biotic homogenisation. Location United States. Time Period 1963–2020. Major Taxa Studied Vascular plants. Methods We used a dataset of more than 70,000 vegetation survey plots to assess differences in biotic homogenisation with and without invasion using both occurrence- and abundance-based metrics of beta diversity. We estimated taxonomic biotic homogenisation by comparing beta diversity of invaded and uninvaded plots with both classes of metrics and investigated the characteristics of the non-native species pool that influenced the likelihood that these metrics disagree. Results In 78% of plot comparisons, occurrence- and abundance-based calculations agreed in direction, and the two metrics were generally well correlated. Our empirical results are consistent with previous theory. Discrepancies between the metrics were more likely when the same non-native species was at high cover at both plots compared for beta diversity, and when these plots were spatially distant. Main Conclusions In about 20% of cases, our calculations revealed differences in direction (homogenisation vs. differentiation) when comparing occurrence- and abundance-based metrics, indicating that the metrics are not interchangeable, especially when distances between plots are high and invader diversity is low. When data permit, combining the two approaches can offer insights into the role of invasions and extirpations in driving biotic homogenisation/differentiation.

Global Ecology and Biogeography