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Abstract and Figures

Recent reports of local extinctions of arthropod species 1 , and of massive declines in arthropod biomass 2 , point to land-use intensification as a major driver of decreasing biodiversity. However, to our knowledge, there are no multisite time series of arthropod occurrences across gradients of land-use intensity with which to confirm causal relationships. Moreover, it remains unclear which land-use types and arthropod groups are affected, and whether the observed declines in biomass and diversity are linked to one another. Here we analyse data from more than 1 million individual arthropods (about 2,700 species), from standardized inventories taken between 2008 and 2017 at 150 grassland and 140 forest sites in 3 regions of Germany. Overall gamma diversity in grasslands and forests decreased over time, indicating loss of species across sites and regions. In annually sampled grasslands, biomass, abundance and number of species declined by 67%, 78% and 34%, respectively. The decline was consistent across trophic levels and mainly affected rare species; its magnitude was independent of local land-use intensity. However, sites embedded in landscapes with a higher cover of agricultural land showed a stronger temporal decline. In 30 forest sites with annual inventories, biomass and species number-but not abundance-decreased by 41% and 36%, respectively. This was supported by analyses of all forest sites sampled in three-year intervals. The decline affected rare and abundant species, and trends differed across trophic levels. Our results show that there are widespread declines in arthropod biomass, abundance and the number of species across trophic levels. Arthropod declines in forests demonstrate that loss is not restricted to open habitats. Our results suggest that major drivers of arthropod decline act at larger spatial scales, and are (at least for grasslands) associated with agriculture at the landscape level. This implies that policies need to address the landscape scale to mitigate the negative effects of land-use practices.
Contribution of individual years to overall trends a, To assess the contribution of individual years to the overall trend, we repeated the linear mixed models for overall biomass, abundance and number of species, and excluded one year each time. The distribution of t and z values for the effect of the year from subset models (white), and from the full models including all years (black), are shown (11 models for grasslands and 10 models for forests). Grey bars denote effect of the year 2008 (the year with the strongest effect on overall trend estimates). b, In addition, we tested whether the observed effect of year differed from a random expectation by randomizing the order of years 100× for forests and grasslands before modelling. The distribution of t and z values for the effect of the year from models with randomly ordered years (white) and models with the years ordered correctly (black) are shown (101 models each for grasslands and forests). Vertical dashed lines indicate levels of significance with P < 0.05. The results in a show that both weaker and stronger temporal trends could be detected when single years were excluded from the analysis, compared to the full model including all years. Results in b show that models with the years ordered randomly produced effects of the year that were normally distributed around zero, and only the models with years ordered correctly generated strong temporal trends. For a more detailed discussion, see Supplementary Information section 3.
Effect of tree mortality on arthropod trends a, The relative change in the number of arthropod species between the first two and the final two study years was similar for managed (n = 19) and unmanaged (n = 9) forest sites (z = 0.648, P = 0.517, derived from a linear mixed model with relative difference in species number as response, harvesting category as fixed and region as random effect). Dots show raw data per site. Boxes represent data within the 25th and 75th percentile, black lines show medians, and whiskers show 1.5× the interquartile range. b, When considering actual tree mortality between forest inventories in 2009 and 2016, declines in the number of arthropod species were weaker at sites with higher tree mortality (z = 2.536, P = 0.011, derived from a linear mixed model with relative difference in species number as response, tree mortality as fixed and region as random effect). Dots show raw data per site. The blue line visualizes the significant relationship between the change in the number of arthropod species and tree mortality based on the linear mixed model, and the shaded area represents confidence intervals. This suggests that changes in habitat conditions and heterogeneity linked to tree mortality—such as increasing canopy openness, herb cover or deadwood availability—moderated declines in the number of arthropod species. More research is needed to identify mechanistic relationships. Tree mortality included both natural mortality and timber harvesting. Forest sites had a stand age of, on average, 116 years (minimum of 30 years and maximum of 180 years) and therefore did not include overmature stands. Owing to stand age and because management was abandoned 20 to 70 years before this study started, natural tree mortality was low even in unmanaged stands. We expect increasingly positive effects of natural tree mortality and associated increased structural diversity and heterogeneity⁴⁰ on arthropod trends with increasing stand age, but further research is required. In Germany, harvesting is usually conducted as shelterwood cutting. In our sites, the harvested amount over the course of our study reached a maximum of 1% of the standing volume per year. More intense harvesting systems (such as clear cutting), which lead to less heterogeneous habitat conditions, may not have similar moderating effects on arthropod declines.
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Nature | Vol 574 | 31 October 2019 | 671
Arthropod decline in grasslands and forests
is associated with landscape-level drivers
Sebastian Seibold1,2*, Martin M. Gossner3, Nadja K. Simons1,4, Nico Blüthgen4, Jörg Müller2,5,
Didem Ambarlı1,6, Christian Ammer7, Jürgen Bauhus8, Markus Fischer9, Jan C. Habel1,10,
Karl Eduard Linsenmair11, Thomas Nauss12, Caterina Penone9, Daniel Prati9, Peter Schall7,
Ernst-Detlef Schulze13, Juliane Vogt1, Stephan Wöllauer12 & Wolfgang W. Weisser1
Recent reports of local extinctions of arthropod species1, and of massive declines in
arthropod biomass2, point to land-use intensication as a major driver of decreasing
biodiversity. However, to our knowledge, there are no multisite time series of
arthropod occurrences across gradients of land-use intensity with which to conrm
causal relationships. Moreover, it remains unclear which land-use types and arthropod
groups are aected, and whether the observed declines in biomass and diversity are
linked to one another. Here we analyse data from more than 1million individual
arthropods (about 2,700species), from standardized inventories taken between 2008
and 2017 at 150grassland and 140forest sites in 3regions of Germany. Overall gamma
diversity in grasslands and forests decreased over time, indicating loss of species
across sites and regions. In annually sampled grasslands, biomass, abundance and
number of species declined by 67%, 78% and 34%, respectively. The decline was
consistent across trophic levels and mainly aected rare species; its magnitude was
independent of local land-use intensity. However, sites embedded in landscapes with a
higher cover of agricultural land showed a stronger temporal decline. In 30forest sites
with annual inventories, biomass and species number—but not abundance—decreased
by 41% and 36%, respectively. This was supported by analyses of all forest sites sampled
in three-year intervals. The decline aected rare and abundant species, and trends
diered across trophic levels. Our results show that there are widespread declines in
arthropod biomass, abundance and the number of species across trophic levels.
Arthropod declines in forests demonstrate that loss is not restricted to open habitats.
Our results suggest that major drivers of arthropod decline act at larger spatial scales,
and are (at least for grasslands) associated with agriculture at the landscape level. This
implies that policies need to address the landscape scale to mitigate the negative
eects of land-use practices.
Much of the debate surrounding the human-induced biodiversity crisis
has focused on vertebrates
, but population declines and extinctions
may be even more substantial in small organisms such as terrestrial
. Recent studies have reported declines in the biomass of
flying insects
, and in the diversity of insect pollinators
, butterflies
and moths
, hemipterans
and beetles
. Owing to the associated
negative effects on food webs
, ecosystem functioning and ecosystem
, this insect loss has spurred an intense public debate. However,
time-series data relating to arthropods are limited, and studies have
so far focused on a small range of taxa11,13,14, a few types of land use and
—or even on single sites
. In addition, many studies lack species
or high temporal resolution
. It therefore remains unclear
whether reported declines in arthropods are a general phenomenon
that is driven by similar mechanisms across land-use types, taxa and
functional groups.
The reported declines are suspected to be caused mainly by human
land use
. Locally, farming practices can affect arthropods directly by
application of insecticides
, mowing
or soil disturbance, or indirectly
via changes in plant communities through the application of herbi-
cides or fertilizer
. Forestry practices can also affect local arthropod
Received: 8 February 2019
Accepted: 16 September 2019
Published online: 30 October 2019
1Terrestrial Ecology Research Group, Department of Ecology and Ecosystem Management, Technical University of Munich, Freising, Germany. 2Field Station Fabrikschleichach, Department of
Animal Ecology and Tropical Biology, Julius-Maximilians-University Würzburg, Würzburg, Germany. 3Forest Entomology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
4Ecological Networks, Department of Biology, Technical University of Darmstadt, Darmstadt, Germany. 5Bavarian Forest National Park, Grafenau, Germany. 6Department of Agricultural
Biotechnology, Faculty of Agricultural and Natural Sciences, Düzce University, Düzce, Turkey. 7Silviculture and Forest Ecology of the Temperate Zones, University of Göttingen, Göttingen,
Germany. 8Institute of Forest Sciences, Faculty of Environment and Natural Resources, University of Freiburg, Freiburg, Germany. 9Institute of Plant Sciences, University of Bern, Bern,
Switzerland. 10Evolutionary Zoology, Biosciences, Salzburg University, Salzburg, Austria. 11Department of Animal Ecology and Tropical Biology, Julius-Maximilians-University Würzburg,
Würzburg, Germany. 12Faculty of Geography, Philipps-University Marburg, Marburg, Germany. 13Max Planck Institute for Biogeochemistry, Jena, Germany. *e-mail:
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... While most studies of temporal trends focus on species richness and/or abundance or occupancy of single groups (e.g., Habel et al., 2019;Janousek et al., 2023;Jönsson et al., 2021), other studies focus solely on the biomass of overall patterns without further taxonomic classification (Hallmann et al., 2017;Müller et al., 2023). The simultaneous assessment of temporal trends in species richness, abundance and biomass is rare (but see Fürst et al., 2022;Seibold et al., 2019). However, evaluating insect diversity trends and their potential consequences for ecosystem functioning and service provisioning is only possible with the joint analysis of richness, abundance and biomass data (Hallmann et al., 2021). ...
... The unmanaged study sites were composed of six unstocked, open study sites and six sites in unmanaged forests. Since patterns in insect trends have been shown to differ between habitats (Seibold et al., 2019), the analysis was conducted separately for the three habitat types. We considered temperature and precipitation as weather-related factors while we employed the normalised difference vegetation index (NDVI) as a land-use related factor. ...
... Our findings seem to contradict the common finding of declining insect richness with time (e.g., Hallmann et al., 2021;Homburg et al., 2019;Powney et al., 2019). For both overall diversity patterns (Hallmann et al., 2017;Seibold et al., 2019) and for different insect taxa, declining patterns are common, also during the 8 years we covered (Habel et al., 2019;Halsch et al., 2021;Janousek et al., 2023). ...
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While many studies on insect diversity report declines, others show stable, fluctuating or increasing trends. For a thorough understanding of insect trends and their effects on ecosystem functioning, it is important to simultaneously assess insect richness, abundance and biomass, and to report trends for multiple taxa. We analysed insect richness, abundance and biomass data for all insects and for eight insect taxa (Buprestidae, Cerambycidae, Carabidae, other Coleoptera, Aculeata, other Hymenoptera, Heteroptera and Lepidoptera) from 42 sites across Switzerland from 2000 to 2007, representing three major habitat types in Switzerland (agricultural, unmanaged [open and forested] and managed forest habitats). As potential drivers of temporal patterns, we evaluated weather‐ and land‐use‐related factors. As predictors, we included temperature and precipitation as well as the vegetation index and the habitat type, respectively. We found a consistent pattern of stable or increasing trends for richness, abundance and biomass of insects in total and the eight taxa over 8 years. Both overall patterns and six out of eight taxa (except for Cerambycidae and Lepidotpera) showed the highest values in agricultural habitats. However, when accounting for elevation, there was no difference in open habitats regardless of whether they were used agriculturally. Habitat types were the most important predictors, followed by weather‐ and vegetation‐related factors. Modelled responses to mean temperature were unimodal, whereas the standard deviation of temperature showed positive and precipitation negative effects. Longer time series are needed to draw robust inferences and to investigate potential negative effects of future warming.
... However, it is known that ecological services by insects such as pollination, decomposition, food supply, and biological pest control are essential to ecosystems [40]. The diversity and abundance of insects have declined in a wide range of habitats and even in nature protected areas (NPA-one of the strictest German categories: "Naturschutzgebiet" and category IV according to IUCN) [13,36,42,53,64]. A multitude of drivers are associated with insect declines, climate change related factors such as droughts, fire, storm intensity, global warming, and interaction disruption or human related effects based on agricultural intensification, deforestation, insecticides, nitrification, pollution, introduced species, and urbanization [50,65]. ...
... The DINA project was initiated to detect causes of insect decline as well as to develop measures to mitigate the decline of flying insects in NPA in Germany (Diversity of Insects in Nature protected Areas, [45]). Previous studies provide support for the assumption that agricultural practices are related to the decline in flying insect biomass [13,53]. Therefore, only NPA with neighbouring or integrated agricultural areas were included in the experimental design to determine if agricultural impact could be verified. ...
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The decline of insect abundance and richness has been documented for decades and has received increased attention in recent years. In 2017, a study by Hallmann and colleagues on insect biomasses in German nature protected areas received a great deal of attention and provided the impetus for the creation of the project Diversity of Insects in Nature protected Areas (DINA). The aim of DINA was to investigate possible causes for the decline of insects in nature protected areas throughout Germany and to develop strategies for managing the problem. A major issue for the protection of insects is the lack of insect-specific regulations for nature protected areas and the lack of a risk assessment and verification of the measures applied. Most nature protected areas border on or enclose agricultural land and are structured in a mosaic, resulting in an abundance of small and narrow areas. This leads to fragmentation or even loss of endangered habitats and thus threaten biodiversity. In addition, the impact of agricultural practices, especially pesticides and fertilisers, leads to the degradation of biodiversity at the boundaries of nature protected areas, reducing their effective size. All affected stakeholders need to be involved in solving these threats by working on joint solutions. Furthermore, agriculture in and around nature protected areas must act to promote biodiversity and utilise and develop methods that reverse the current trend. This also requires subsidies from the state to ensure economic sustainability and promote biodiversity-promoting practices.
... Consequently, the status of insects is critical for the functioning of many ecosystems, and their decline can have strong cascading effects on other trophic levels (e.g., Rosenberg et al., 2019). Such declines, both in abundance and diversity, have been well documented for the past half-century, especially in temperate regions of North America and Europe (Hallmann et al., 2017;Seibold et al., 2019;van Klink et al., 2020;Wagner, 2020). ...
Land use change, as a result of many local-scale decisions scaling up to large spatial extents, is considered the main threat to European butterflies. The impact of large-scale pressures, such as atmospheric nitrogen deposition or climate change, is less understood or less documented, respectively. However, it is acknowledged that they might reinforce the pressure on already threatened species. To evaluate the additional threat exerted by these pressures we compared their geographical pattern to those of threatened butterflies across Europe. We therefore derived range maps of 383 butterfly species and used two species-specific threat assessments derived from national and European Red Lists. We then used Spearman rank-correlations and beta-regressions to compare two metrics of species threat per 10 × 10 km raster cells with geographical patterns of cumulative nitrogen de-positions from 1980 to 2015, as well as the magnitude of change in precipitation sums and temperature means between the decades 1979-1988 and 2004-2013. We found that threatened species tend to concentrate in areas with high nitrogen depositions and pronounced summer temperature changes. In particular, parts of central and eastern Europe were both hotspots of threatened butterflies and hotspots of climatic pressure. This spatial coincidence of the distribution of threatened butterfly species with large-scale patterns of nitrogen depositions and recent climate warming indicates an already considerable risk of regional to continental extinctions that will likely increase further in the future as climate change will most likely intensify. Consequences for area-based conservation measures are discussed.
... Bumblebees (genus: Bombus) are among the most important pollinators on the planet, playing a vital role in maintaining biodiversity, the health of natural ecosystems, and agricultural food production [1]. However, recent reports of significant declines in insect abundance and biodiversity have raised global attention over the decline of bumblebees [2][3][4][5][6][7][8][9]. There are multiple reports of bumblebee declines in Asia [10,11], Europe [12][13][14], North America [15][16][17][18], and South America [19,20]. ...
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Simple Summary Our study investigated the dynamics of pathogen communities within Chinese bumblebee populations, a key issue for understanding emerging infectious diseases and their impacts on insect biodiversity loss. By employing computational modeling on extensive pathogen data from bumblebees, we uncover that the host species variation significantly influences pathogen assembly and occurrences, compared to environmental factors like climate and location. Moreover, our results reveal significant pathogen–pathogen interactions, with similar pathogens exhibiting facilitatory relationships and distinct pathogen types showing strong negative associations, possibly due to immune response interactions and competitive dynamics within hosts. Our findings highlight the role of host–pathogen coevolution and other ecological interactions in shaping pathogen communities. The implications of this work are substantial for bumblebee conservation, improving our understanding of pathogen dynamics that could inform strategies to stop declines in bumblebee populations. Abstract Bumblebees have been considered one of the most important pollinators on the planet. However, recent reports of bumblebee decline have raised concern about a significant threat to ecosystem stability. Infectious diseases caused by multiple pathogen infections have been increasingly recognized as an important mechanism behind this decline worldwide. Understanding the determining factors that influence the assembly and composition of pathogen communities among bumblebees can provide important implications for predicting infectious disease dynamics and making effective conservation policies. Here, we study the relative importance of biotic interactions versus interspecific host resistance in shaping the pathogen community composition of bumblebees in China. We first conducted a comprehensive survey of 13 pathogens from 22 bumblebee species across China. We then applied joint species distribution modeling to assess the determinants of pathogen community composition and examine the presence and strength of pathogen–pathogen associations. We found that host species explained most of the variations in pathogen occurrences and composition, suggesting that host specificity was the most important variable in predicting pathogen occurrences and community composition in bumblebees. Moreover, we detected both positive and negative associations among pathogens, indicating the role of competition and facilitation among pathogens in determining pathogen community assembly. Our research demonstrates the power of a pluralistic framework integrating field survey of bumblebee pathogens with community ecology frameworks to understand the underlying mechanisms of pathogen community assembly.
... [3] For example, a 10-year study carried out in Germany revealed that in annually sampled grasslands, after ten years the biomass, abundance, and number of species have declined by 67%, 78%, and 34%, respectively. [4] This also means that pollinator insect populations are declining, threatening both ecosystem functions and human food supplies. The decline of insects has several major drivers such as loss of habitat due to conversion into agriculture and urbanization, massive use of agrochemicals such as insecticides and fertilizers, climate change, and biological factors such as invasive species. ...
Full-text available
Synthetic insecticides are widely used against plant pest insects to protect the crops. However, many insecticides have poor selectivity and are toxic also to beneficial insects, animals, and humans. In addition, insecticide residues can remain on fruits for many days, jeopardizing food safety. For these reasons, a reusable, low‐cost electronic trap that can attract, detect, and identify, but attack only the pest while leaving beneficial insects unharmed could provide a sustainable, nature‐friendly replacement. Here, for the first time, research results are presented suggesting the great potential and compatibility of organic electronic devices and technologies with pest management. Electrical characterizations confirm that an insect's body has relatively high dielectric permittivity. Adaptive memcapacitor circuits can track the impedance change for insect detection. Other experiments show that printed polymer piezoelectric transducers on a plastic substrate can collect information about the weight and activity of insects for identification. The breakdown voltage of most insects´ integument is measured to be <200 V. Long channel organic transistors easily work at such high voltages while being safe to touch for humans thanks to their inherent low current. This feasibility study paves the way for the future development of organic electronics for physical pest control and biodiversity protection.
... In 2017, Hallmann and colleagues estimated that the total flying insect biomass on German nature reserves decreased by 82 % in midsummer over a 27-year period (Hallmann et al., 2017). More recently, Seibold et al. (2019) found that arthropod biomass in Germany declined by 67 %, arthropod abundance reduced by 78 % and the number of arthropod species decreased by 34 % in grassland between 2008 and 2017. Overall, there is a strong consensus that insect populations appear to be undergoing rapid decline across Europe, North America and probably elsewhere (Wagner et al., 2021). ...
Full-text available
Most people today live in cities1, and cities are planned primarily for the benefit of humans. Yet, cities also provide habitat to many other species2–6. There is a growing agreement on the need to safeguard urban biodiversity7–9, and that urban green is important for the occurrence of species in cities10. Urban green has many components, and our understanding of how these and other features of the built-up area of cities enable different taxa to live in the city remains limited3,11. Here we show for the city of Munich that designed features of public urban squares strongly determine the occurrence of different taxa, including arthropods, bats, birds, mosses, pollinators, small mammals, and herbaceous plants. Generally, taxon richness and abundance increased with increasing ‘greenness’ of the square. Yet, different taxa responded to different square features, such as the proportion of lawn, shrub volume and tree density. Square size and position in the city affected several taxa as did human use of squares and artificial light at night. Our results underline that the way humans design the city for their own needs affects other species that potentially cohabit these spaces. Consequently, planning strategies for biodiverse cities aiming to increase human-nature interactions12,13 and the provisioning of ecosystem services need to be multifaceted, considering the needs of humans and other taxa to create diverse living cities.
Our limited knowledge about the ecological drivers of global arthropod decline highlights the urgent need for more effective biodiversity monitoring approaches. Monitoring of arthropods is commonly performed using passive trapping devices, which reliably recover diverse communities, but provide little ecological information on the sampled taxa. Especially the manifold interactions of arthropods with plants are barely understood. A promising strategy to overcome this shortfall is environmental DNA (eDNA) metabarcoding from plant material on which arthropods leave DNA traces through direct or indirect interactions. However, the accuracy of this approach has not been sufficiently tested. In four experiments, we exhaustively test the comparative performance of plant‐derived eDNA from surface washes of plants and homogenized plant material against traditional monitoring approaches. We show that the recovered communities of plant‐derived eDNA and traditional approaches only partly overlap, with eDNA recovering various additional taxa. This suggests eDNA as a useful complementary tool to traditional monitoring. Despite the differences in recovered taxa, estimates of community α‐ and β‐diversity between both approaches are well correlated, highlighting the utility of eDNA as a broad scale tool for community monitoring. Last, eDNA outperforms traditional approaches in the recovery of plant‐specific arthropod communities. Unlike traditional monitoring, eDNA revealed fine‐scale community differentiation between individual plants and even within plant compartments. Especially specialized herbivores are better recovered with eDNA. Our results highlight the value of plant‐derived eDNA analysis for large‐scale biodiversity assessments that include information about community‐level interactions.
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Biodiversity is declining at alarming rates worldwide and large-scale monitoring is urgently needed to understand changes and their drivers. While classical taxonomic identification of species is time and labour intensive, the combination with DNA-based methods could upscale monitoring activities to achieve larger spatial coverage and increased sampling effort. However, challenges remain for DNA-based methods when the number of individuals per species and/or biomass estimates are required. Several methodological advancements exist to improve the potential of DNA metabarcoding for abundance analysis, which however need further evaluation. Here, we discuss laboratory, as well as some bioinformatic adjustments to DNA metabarcoding workflows regarding their potential to achieve species abundance estimation from arthropod community samples. Our review includes pre-laboratory processing methods such as specimen photography, laboratory methods such as the use of spike-in DNA as an internal standard and bioinformatic advancements like correction factors. We conclude that specimen photography coupled with DNA metabarcoding currently promises the greatest potential to achieve estimates of the number of individuals per species and biomass estimates, but that approaches such as spike-ins and correction factors are promising methods to pursue further.
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In this study, we aim to uncover diet preferences for the insectivorous bat Nyctalus leisleri (Leisler's bat, the lesser noctule) and to provide recommendations for conservation of the species, based on the analysis of prey source habitats. Using a novel guano trap, we sampled bat faeces at selected roosts in a forest in Germany and tested two mitochondrial markers (COI and 16S) and three primer pairs for the metabarcoding of bat faecal pellets. We found a total of 17 arthropod prey orders comprising 358 species in N. leisleri guano. The most diverse orders were Lepidoptera (126 species), Diptera (86 species) and Coleoptera (48 species), followed by Hemiptera (28 species), Trichoptera (16 species), Neuroptera (15 species) and Ephemeroptera (10 species), with Lepidoptera species dominating in spring and Diptera in summer. Based on the ecological requirements of the most abundant arthropod species found in the bat guano, we propose some recommendations for the conservation of N. leisleri that are relevant for other insectivorous bat species.
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While forest management strongly influences biodiversity, it remains unclear how the structural and compositional changes caused by management affect different community dimensions (e.g. richness, specialisation, abundance or completeness) and how this differs between taxa. We assessed the effects of nine forest features (representing stand structure, heterogeneity and tree composition) on thirteen above-and belowground trophic groups of plants, animals, fungi and bacteria in 150 temperate forest plots differing in their management type. Canopy cover decreased light resources, which increased community specialisation but reduced overall diversity and abundance. Features increasing resource types and diversifying microhabitats (admixing of oaks and conifers) were important and mostly affected richness. Belowground groups responded differently to those aboveground and had weaker responses to most forest features. Our results show that we need to consider forest features rather than broad management types and highlight the importance of considering several groups and community dimensions to better inform conservation.
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The successional dynamics of forests—from canopy openings to regeneration, maturation, and decay—influence the amount and heterogeneity of resources available for forest‐dwelling organisms. Conservation has largely focused only on selected stages of forest succession (e.g., late‐seral stages). However, to develop comprehensive conservation strategies and to understand the impact of forest management on biodiversity, a quantitative understanding of how different trophic groups vary over the course of succession is needed. We classified mixed mountain forests in Central Europe into nine successional stages using airborne Li DAR . We analysed α‐ and β‐diversity of six trophic groups encompassing approximately 3,000 species from three kingdoms. We quantified the effect of successional stage on the number of species with and without controlling for species abundances and tested whether the data fit the more‐individuals hypothesis or the habitat heterogeneity hypothesis. Furthermore, we analysed the similarity of assemblages along successional development. The abundance of producers, first‐order consumers, and saprotrophic species showed a U‐shaped response to forest succession. The number of species of producer and consumer groups generally followed this U‐shaped pattern. In contrast to our expectation, the number of saprotrophic species did not change along succession. When we controlled for the effect of abundance, the number of producer and saproxylic beetle species increased linearly with forest succession, whereas the U‐shaped response of the number of consumer species persisted. The analysis of assemblages indicated a large contribution of succession‐mediated β‐diversity to regional γ‐diversity. Synthesis and applications . Depending on the species group, our data supported both the more‐individuals hypothesis and the habitat heterogeneity hypothesis. Our results highlight the strong influence of forest succession on biodiversity and underline the importance of controlling for successional dynamics when assessing biodiversity change in response to external drivers such as climate change. The successional stages with highest diversity (early and late successional stages) are currently strongly underrepresented in the forests of Central Europe. We thus recommend that conservation strategies aim at a more balanced representation of all successional stages.
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Global declines in insects have sparked wide interest among scientists, politicians, and the general public. Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services. Our understanding of the extent and underlying causes of this decline is based on the abundance of single species or taxo-nomic groups only, rather than changes in insect biomass which is more relevant for ecological functioning. Here, we used a standardized protocol to measure total insect biomass using Malaise traps, deployed over 27 years in 63 nature protection areas in Germany (96 unique location-year combinations) to infer on the status and trend of local entomofauna. Our analysis estimates a seasonal decline of 76%, and midsummer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline. This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape.
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1. For managed temperate forests, conservationists and policymakers favour fine-grained uneven-aged management over more traditional coarse-grained even-aged management, based on the assumption that within-stand habitat heterogeneity enhances biodiversity. There is, however, little empirical evidence to support this assumption. We investigated for the first time how differently grained forest management systems affect the biodiversity of multiple above- and below-ground taxa across spatial scales. 2. We sampled 15 taxa of animals, plants, fungi and bacteria within the largest contiguous beech forest landscape of Germany and classified them into functional groups. Selected forest stands have been managed for more than a century at different spatial grains. The even-aged (coarse-grained management) and uneven-aged (fine-grained) forests are comparable in spatial arrangement, climate and soil conditions. These were compared to forests of a nearby national park that have been unmanaged for at least 20 years. We used diversity accumulation curves to compare γ-diversity for Hill-numbers 0D (species richness), 1D (Shannon diversity) and 2D (Simpson diversity) between the management systems. Beta diversity was quantified as multiple-site dissimilarity. 3. Gamma diversity was higher in even-aged than in uneven-aged forests for at least one of the three Hill-numbers for six taxa (up to 77%), while eight showed no difference. Only bacteria showed the opposite pattern. Higher γ-diversity in even-aged forests was also found for forest specialists and saproxylic beetles. 4. Between-stand β-diversity was higher in even-aged than in uneven-aged forests for one third (all species) and half (forest specialists) of all taxa, driven by environmental heterogeneity between age-classes, while α-diversity showed no directional response across taxa or for forest specialists. 5. Synthesis and applications. Comparing even-aged and uneven-aged forest management in Central European beech forests, our results show that a mosaic of different age-classes is more important for regional biodiversity than high within-stand heterogeneity. We suggest reconsidering the current trend of replacing even-aged management in temperate forests. Instead, the variability of stages and stand structures should be increased to promote landscape scale biodiversity.
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Along with the global decline of species richness goes a loss of ecological traits. Associated biotic homogenization of animal communities and narrowing of trait diversity threaten ecosystem functioning and human well‐being. High management intensity is regarded as an important ecological filter, eliminating species that lack suitable adaptations. Below‐ground arthropods are assumed to be less sensitive to such effects than above‐ground arthropods. Here, we compared the impact of management intensity between (grassland vs. forest) and within land‐use types (local management intensity) on the trait diversity and composition in below‐ and above‐ground arthropod communities. We used data on 722 arthropod species living above‐ground (Auchenorrhyncha and Heteroptera), primarily in soil (Chilopoda and Oribatida) or at the interface (Araneae and Carabidae). Our results show that trait diversity of arthropod communities is not primarily reduced by intense local land use, but is rather affected by differences between land‐use types. Communities of Auchenorrhyncha and Chilopoda had significantly lower trait diversity in grassland habitats as compared to forests. Carabidae showed the opposite pattern with higher trait diversity in grasslands. Grasslands had a lower proportion of large Auchenorrhyncha and Carabidae individuals, whereas Chilopoda and Heteroptera individuals were larger in grasslands. Body size decreased with land‐use intensity across taxa, but only in grasslands. The proportion of individuals with low mobility declined with land‐use intensity in Araneae and Auchenorrhyncha, but increased in Chilopoda and grassland Heteroptera. The proportion of carnivorous individuals increased with land‐use intensity in Heteroptera in forests and in Oribatida and Carabidae in grasslands. Our results suggest that gradients in management intensity across land‐use types will not generally reduce trait diversity in multiple taxa, but will exert strong trait filtering within individual taxa. The observed patterns for trait filtering in individual taxa are not related to major classifications into above‐ and below‐ground species. Instead, ecologically different taxa resembled each other in their trait diversity and compositional responses to land‐use differences. These previously undescribed patterns offer an opportunity to develop management strategies for the conservation of trait diversity across taxonomic groups in permanent grassland and forest habitats.
Evidence of declines in insect populations has recently received considerable scientific and societal attention. However, the lack of long-term insect monitoring makes it difficult to assess whether declines are geographically widespread. By contrast, bird populations are well monitored and often used as indicators of environmental change. We compared the population trends of European insectivorous birds with those of other birds to assess whether patterns in bird population trends were consistent with declines of insects. We further examined whether declines were evident for insectivores with different habitats, foraging strata, and other ecological preferences. Bird population trends were estimated for Europe (1990-2015) and Denmark (1990-2016). On average, insectivores declined over the study period (13% across Europe and 28% in Denmark), whereas omnivores had stable populations. Seedeaters also declined (28% across Europe; 34% in Denmark), but this assessment was based on fewer species than for other groups. The effects of insectivory were stronger for farmland species (especially grassland species), for ground feeders, and for cold-adapted species. Insectivory was associated with long-distance migration, which was also linked to population declines. However, many insectivores had stable populations, especially habitat generalists. Our findings suggest that the decline of insectivores is primarily associated with agricultural intensification and loss of grassland habitat. The loss of both seed and insect specialists indicates an overall trend toward bird communities dominated by diet generalists. © 2019 Society for Conservation Biology.
Land-use intensification is a major driver of biodiversity loss. Alongside reductions in local species diversity, biotic homogenization at larger spatial scales is of great concern for conservation. Biotic homogenization means a decrease in β-diversity (the compositional dissimilarity between sites). Most studies have investigated losses in local (α)-diversity and neglected biodiversity loss at larger spatial scales. Studies addressing β-diversity have focused on single or a few organism groups (for example, ref. 4), and it is thus unknown whether land-use intensification homogenizes communities at different trophic levels, above- and belowground. Here we show that even moderate increases in local land-use intensity (LUI) cause biotic homogenization across microbial, plant and animal groups, both above- and belowground, and that this is largely independent of changes in α-diversity. We analysed a unique grassland biodiversity dataset, with abundances of more than 4,000 species belonging to 12 trophic groups. LUI, and, in particular, high mowing intensity, had consistent effects on β-diversity across groups, causing a homogenization of soil microbial, fungal pathogen, plant and arthropod communities. These effects were nonlinear and the strongest declines in β-diversity occurred in the transition from extensively managed to intermediate intensity grassland. LUI tended to reduce local α-diversity in aboveground groups, whereas the α-diversity increased in belowground groups. Correlations between the β-diversity of different groups, particularly between plants and their consumers, became weaker at high LUI. This suggests a loss of specialist species and is further evidence for biotic homogenization. The consistently negative effects of LUI on landscape-scale biodiversity underscore the high value of extensively managed grasslands for conserving multitrophic biodiversity and ecosystem service provision. Indeed, biotic homogenization rather than local diversity loss could prove to be the most substantial consequence of land-use intensification.
Environmental changes strongly impact the distribution of species and subsequently the composition of species assemblages. Although most community ecology studies represent temporal snap shots, long-term observations are rather rare. However, only such time series allow the identification of species composition shifts over several decades or even centuries. We analyzed changes in the species composition of a southeastern German butterfly and burnet moth community over nearly 2 centuries (1840-2013). We classified all species observed over this period according to their ecological tolerance, thereby assessing their degree of habitat specialisation. This classification was based on traits of the butterfly and burnet moth species and on their larval host plants. We collected data on temperature and precipitation for our study area over the same period. The number of species declined substantially from 1840 (117 species) to 2013 (71 species). The proportion of habitat specialists decreased, and most of these are currently endangered. In contrast, the proportion of habitat generalists increased. Species with restricted dispersal behavior and species in need of areas poor in soil nutrients had severe losses. Furthermore, our data indicated a decrease in species composition similarity between different decades over time. These data on species composition changes and the general trends of modifications may reflect effects from climate change and atmospheric nitrogen loads, as indicated by the ecological characteristics of host plant species and local changes in habitat configuration with increasing fragmentation. Our observation of major declines over time of currently threatened and protected species shows the importance of efficient conservation strategies.
Cereal fields are central to balancing food production and environmental health in the face of climate change. Within them, invertebrates provide key ecosystem services. Using 42 years of monitoring data collected in Southern England, we investigated the sensitivity and resilience of invertebrates in cereal fields to extreme weather events and examined the effect of long-term changes in temperature, rainfall and pesticide use on invertebrate abundance. Of the 26 invertebrate groups examined, eleven proved sensitive to extreme weather events. Average abundance increased in hot/dry years and decreased in cold/wet years for Araneae, Cicadellidae, adult Heteroptera, Thysanoptera, Braconidae, Enicmus and Lathridiidae. The average abundance of Delphacidae, Cryptophagidae and Mycetophilidae increased in both hot/dry and cold/wet years relative to other years. The abundance of all 10 groups usually returned to their long-term trend within a year after the extreme event. For five of them sensitivity to cold/wet events was lowest (translating into higher abundances) at locations with a westerly aspect. Some long-term trends in invertebrate abundance correlated with temperature and rainfall, indicating that climate change may affect them. However, pesticide use was more important in explaining the trends, suggesting that reduced pesticide use would mitigate the effects of climate change. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.