The cover image relates to the Research Article https://doi.org/10.1111/ddi.13912 “A race against extinction: The challenge to overcome the Linnean amphibian shortfall in tropical biodiversity hotspots” by Carné et al. A Malagasy treefrog from the genus Boophis (B. aff. madagascariensis) recorded in Marojejy National Park, Northern Madagascar. Image Credit: Albert Carné.
As climate change increasingly threatens the world's coral reefs, enhancing their resilience by improving population connectivity for key reef species is crucial for ensuring their persistence. Here, we evaluate the population genomic structure of two common coral species, Pocillopora acuta and Porites sp., chosen due to their divergent life histories. Thousands of single-nucleotide polymorphisms (SNPs) were sequenced and analysed to infer regional connectivity patterns in Southeast Asia, a region that harbours a tremendous diversity of marine life.
Coasts of the Malay Peninsula and northern Borneo, covering ~1 million km2.
NextRAD genotyping-by-sequencing of 185 Porites sp. and 221 Pocillopora acuta colonies. Libraries were prepared and sequenced on Illumina NovaSeq 6000. Genotyping involved initial quality controls, allele frequency filtering and checks for contamination. Genetic structure was assessed with Bayesian clustering, and relationships between genetic variation and environmental factors were studied through redundancy analysis. Contemporary gene flow was estimated using BayesAss.
We observed panmixia among the broadcasting Porites sp. populations, while for the brooding Pocillopora acuta, the Malay Peninsula acts a strong barrier to dispersal between the Malacca Strait and the southern South China Sea. Moreover, its genomic structure seems to follow current marine ecoregion delineation. By analysing contemporary migrant movement, we can prioritise reef localities for conservation. In particular, localities at the Andaman Coral Coast are contemporarily isolated from the other localities, and Tioman is identified as a major larval source for both species.
Our analyses highlight contrasting population differentiation patterns between the two species that can be explained by the disparity in their reproductive strategies. These findings are important for biodiversity managers in Southeast Asia; incorporation of regional connectivity considerations into conservation planning can help safeguard ecosystem resilience and persistence.
The enemy release hypothesis states that the invasion success of non-native species is partly due to their escape from natural enemies, e.g., herbivores. Large-scale studies of herbivory using multiple species across multiple sites are needed to test the generality of herbivory release in non-native plants.
Europe.
We carried out leaf-herbivory surveys from 2007 to 2021 in 15 botanical gardens ranging in latitude from 47°N (Switzerland) to 63°N (Norway) to investigate how herbivory levels differed between (i) native and non-native species, and (ii) native and non-naturalised or naturalised species.
Overall, we found that herbivory levels were lower on non-native than native species. In addition, we found that non-naturalised plants suffered less herbivory than natives and that naturalised plants showed similar levels of herbivory to native plants.
We find broad support for lower herbivory of non-native plant species compared to natives. However, the stronger reduction in herbivory for non-naturalised plants suggests that herbivore release may be transient and less pronounced for naturalised non-native species that have become abundant and integrated into resident communities. This has implications for the management of naturalised non-native plants, which are performing well in their non-native ranges despite suffering comparable herbivory levels to native species.
Habitat destruction causes “extinction debt” and is also thought to produce ecosystem function debt, but theory of their magnitude and nature is limited. Heterogeneous landscapes are fundamental to the maintenance of species richness and ecosystem function, while directed or undirected dispersal behaviour, such as dispersal of seeds by animals or by the wind, is also important, especially after habitat destruction. We therefore consider extinction and ecosystem function debt under different dispersal rates and behaviours in heterogeneous landscapes.
We use a classic heterogeneous metacommunity model to capture the dynamics of competing species in local patches linked by dispersal and varying in environmental conditions. We remove one patch at a time and measure extinction debt and ecosystem function debt by the number/proportion of delayed extinctions and the amount of biomass change, respectively.
We reveal three species extinction regimes as dispersal increases: (1). species most adapted to the removed habitat are most at risk; (2). similarly adapted species are also at risk; (3). patch removal shifts competitive balance among the few species coexisting at high dispersal, where competition is strong. We find surprisingly that destruction of habitat can hasten the extinction of those species best adapted to harsh environments and that the proportion of diversity at risk from extinction actually increases with dispersal because competition is intense there. Finally, there can be a small ecosystem credit but extinction debt when dispersers reroute to potentially more favourable remaining habitats (directed dispersal), especially when harsh environments are removed. However, ecosystem debt occurs and can be large under undirected dispersal.
The magnitude and nature of extinction and ecosystem function debts depend on species dispersal rates and behaviours, as well as the environmental conditions of the disturbed habitats. Conservation actions will be more successful if they consider these factors.
Human activities pose many challenges to freshwater biodiversity. Among these, is landscape transformation, such as conversion of natural grassland to plantation forestry, impacting both terrestrial and freshwater biodiversity. Functional diversity measures provide substantial information on current and emerging impacts on biological communities, and aid conservation decisions relative to anthropogenic impacts. We determined (1) environmental similarities among 10 freshwater biotope types; (2) whether freshwater biotopes in conservation corridor networks support equal levels of functional richness and divergence compared with an extensive neighbouring protected area; (3) whether certain biotopes are more important for maintaining functional richness and divergence than others; and (4) whether associations between traits and biotope types could be identified.
The northeastern coastal region of South Africa.
Using dragonflies as model organisms, and data from 140 freshwater lotic and lentic sites, we investigated the distribution of dragonfly traits across a plantation forestry-natural grassland landscape mosaic with a range of biotope types.
Lake sites were different in their environmental conditions compared with the other biotopes. Environmental conditions were variable among the other biotope types and were difficult to distinguish. Freshwater biotopes in the conservation corridors supported equal levels of functional richness and divergence compared with those in the protected area. Overall, dragonfly functional richness and divergence were low at lake sites and wallows, while all other biotopes supported high levels of functional richness and divergence. Trait associations were complex across the waterscape and driven by habitat selection, flight behaviour and ecological sensitivity.
Maintaining a mosaic of small lentic and lotic habitats would best support dragonfly conservation in this transformed landscape. A combination of biotopes offers a wide range of environmental conditions essential for conserving the full range of dragonfly traits and species across the region.
People have strongly influenced the biosphere for millennia, but how their increasing activities have shaped wildlife distribution is incompletely understood. We examined how the distribution of European large (>8 kg), wild mammals has changed in association with changing anthropogenic pressures and climate change through the Holocene.
Europe.
We used over 17,000 zooarchaeological records of 20 species spanning 12,000 years to develop time-calibrated species distribution models, incorporating dynamic data on cropland extent, natural vegetation fragmentation, human population density and climate. We assessed habitat availability and potential species richness across time and within seven biogeographical regions. We also compared anthropogenic pressures at zooarchaeological record sites with present-day habitats of remaining large mammals to evaluate recent increases in their potential for coexistence with human activities.
We found a continuous decline in potential large mammal species richness, particularly linked to changes in human population density. Most habitat loss became evident continentally after 1500 AD, but in the Atlantic and Mediterranean bioregions, habitat loss reached 20% during the Iron/Roman Ages (1000 BC–500 AD) due to increasing human population density. Climate change initially boosted species richness (+0.67 species/km2 on average) until the end of the Mesolithic but had negligible effects afterward. Today, large mammals appear to have a higher potential for coexisting with people compared to the past (e.g., herbivores today inhabit areas with a mean human population density of 95 people/km2, compared to an average of 17 people/km2 in the period 1500–2000 AD).
Our study emphasizes the crucial role of anthropogenic pressures over natural climate change in determining the distribution and diversity of large mammal communities throughout history. Additionally, our results indicate that contemporary anthropogenic trends like land-use de-intensification and stronger conservation policies can counteract the impact of past, higher anthropogenic pressures and reverse defaunation.
We assessed the juvenile climatic niche breadth of a relict mountain species by comparing field observations and transplant experiments within and beyond the elevational limits of its distribution range.
Lebanon – Near East – Mediterranean region.
We studied the survival and growth of the Cedar of Lebanon (Cedrus libani) to determine the lower and upper elevational range limits of its juvenile stage through an experimental setup with and without water supplementation and with potentially competing species as a control. The experiment included eight common gardens at elevations ranging from 110 to 2330 m, within and far beyond the warm and cold limits of Cedar distribution observed under natural conditions.
We observed unexpectedly high survival and growth rates of Cedar at elevations well below the range of its natural distribution in Lebanon. Below the observed warm limit, water stress at very low elevations and competition at low and medium elevations limited juvenile survival. In contrast, cold temperature and water stress limited survival at elevations slightly above the observed upper natural limit. The experimental setup demonstrated that the elevation range suitable for Cedar growth and survival was twice as wide as the range within which Cedar is observed under natural conditions.
High survival rates experimentally observed beyond the warm limit of the natural distribution range of the Cedar of Lebanon raise hope for its resilience to ongoing climate warming. If this pattern were frequent among montane species, it would challenge predictions of massive extinction with climate change and pave the way for promoting adaptive actions such as competition management to improve their survival.
Species presence–absence data can be time-consuming and logistically difficult to obtain across large spatial extents. Yet these data are important for ensuring changes in species distributions are accurately monitored and are vital for ensuring appropriate conservation actions are undertaken. Here, we demonstrate how environmental DNA (eDNA) sampling can be used to systematically collect species occupancy data rapidly and efficiently across vast spatial domains to improve understanding of factors influencing species distributions.
South-eastern Australia.
We use a widely distributed, but near-threatened species, the platypus (Ornithorhynchus anatinus), as a test case and undertake an environmentally stratified systematic survey to assess the presence–absence of platypus eDNA at 504 sites across 584,292 km2 of south-eastern Australia, representing ~37% of the species' extensive distribution. Site occupancy-detection models were used to analyse how landscape- and site-level factors affect platypus occupancy, enabling us to incorporate uncertainty at the different levels inherent in eDNA sampling (site, water sample replicate and qPCR replicate).
Platypus eDNA was detected at 272 sites (~54%) with platypuses more likely to occupy sites in catchments with increased runoff and less zero-flow days, and sites with access to banks suitable for burrowing. Platypuses were less likely to occupy sites in catchments with a high proportion of shrubs and grasslands, or agricultural land use.
These data provide an important large-scale validation of the landscape- and site-level factors influencing platypus occupancy that can be used to inform future conservation efforts. Our case study shows that systematically designed, stratified eDNA surveys provide an efficient means to understand how environmental characteristics affect species occupancy across broad environmental gradients. The methods employed here can be applied to aquatic and semi-aquatic species globally, providing unprecedented opportunities to understand biodiversity status and change and provide insights for current and future conservation actions.
Population dynamics are usually assessed through linear trend analysis, quantifying their general direction. However, linear trends may hide substantial variations in population dynamics that could reconcile apparent discrepancies when quantifying the extent of the biodiversity crisis. We seek to determine whether the use of non-linear methods and the quantification of temporal variability can offer a more complete representation of changes in global population dynamics than commonly-used linear approaches.
We analysed 6437 population time series from 1257 vertebrate species from the Living Planet Database over the period 1950–2020. We modelled populations through the use of second-order polynomials and classified trajectories according to their direction and acceleration. We modelled and classified these same populations using a more classical linear trend analysis. We quantified temporal variability using the mean squared error of the fitted polynomials. We then used generalised linear mixed models to test potential sources of heterogeneity in non-linear trajectories and temporal variability.
In all, 44.8% of the analysed population time series were non-linear. Across all populations, 30% were declining, 30% were increasing, and 40% were with no linear trend. Among the population showing no linear trend, half were concave or convex. Non-linearity was expressed differently between taxonomic groups, with mammals showing higher prevalence of non-linearity. Marine and freshwater populations were more variable than terrestrial populations, and fish were more variable than other vertebrates. Differences between geographical regions were detected in both non-linearity and temporal variability, but no straightforward pattern emerged. There were no differences in both components between IUCN categories.
Non-linearity and temporal variability reveal usually overlooked dramatic declines or recovery signals in global population dynamics. Thus, moving beyond linearity can improve our understanding of complex population dynamics and better inform conservation decisions. In particular, populations usually classified as ‘stable’ can hide informative changes in non-linear and variability patterns that need to be considered in global biodiversity assessments.
Rapid technological advancements and the biodiversity crisis have motivated efforts to document species before their extinction. However, taxonomic coverage gaps, where certain species are underrepresented in biodiversity databases, can distort our understanding of ecosystems. Here, we quantified how many of the plant species found in a hotspot are invisible, i.e. they would be excluded from studies due to insufficient occurrence data. Additionally, we identified factors influencing the invisibility of species.
Atlantic Forest hotspot, Brazil.
We downloaded and filtered occurrence data from 15,010 plant species from online biodiversity databases. We utilized multiple thresholds, each representing a minimum required number of records, to classify species as “invisible” if their record count fell below these thresholds. We fitted logistic models to estimate how factors such as life form, presence of a vernacular name, geographical distribution, endemism, and year of taxonomic publication influence the odds of species exclusion.
The proportion of invisible species ranged from 14% when employing simple tools requiring just three records to as high as 64% with more demanding tools requiring at least 60 records. Species with specific characteristics are more prone to invisibility, including non-tree species, species without vernacular names, species with restricted distributions within Atlantic Forest, endemic species, and species with names published more recently. A significant portion of these invisible species are distributed along the coastline. In contrast, the continental portion of the biome exhibits fewer taxonomic coverage gaps of known species, most likely due to lower rates of new species descriptions.
Coverage gaps are shaped by the interaction of biological traits, societal preferences, limited technical support, and human activities. Studies relying on distributional data must balance the rigour of filters and thresholds to achieve both geographical reliability and taxonomic coverage, adjusting them to align with each study's specific data and goals.
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