Arthropod decline in grasslands and forests is associated with landscape-level drivers.

Recent reports of local extinctions of arthropod species1, and of massive declines in arthropod biomass2, 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.

Determinants of Termite Assemblages' Characteristics within Natural Habitats of a Sudano-Guinean Savanna (Comoe National Park, Côte d'Ivoire).

Termites are one of the major components of tropical ecosystems. However, the ecological and biological variables determining the structure of their communities within natural habitats are less documented in general and especially in the Comoe National Park, a Sudano-Guinean savanna zone located in the north-eastern part of Côte d'Ivoire (West Africa). Using a standardized method of belt transects, the structure of termite's communities was estimated within habitats differing in the structure of their vegetation, soil characteristics, and the disturbance level caused by annual occurrences of bushfires. The effect of a set of environmental variables (habitat type, occurrence of annual bushfire, woody plant density, woody plant species richness, and soil physicochemical parameters) was tested on the habitat-specific recorded termite species. Sixty species of termites belonging to 19 genera, seven subfamilies and two families, namely Rhinotermitidae (Coptotermitinae and Rhinotermitinae) and Termitidae (Apicotermitinae, Cubitermitinae, Macrotermitinae, Nasutitermitinae, and Termitinae) were sampled. These species were assigned to the four feeding groups of termites: fungus growers (18 species), wood feeders (17 species), soil feeders (19 species) and the grass feeders (6 species). The highest diversity of termites was encountered in forest habitats, with 37 and 34, respectively, for the gallery forest and the forest island. Among savanna habitats, the woodland savanna was identified as the most diversified habitat with 32 recorded species, followed by the tree savanna (28 species) and the grassy savanna (17 species). The distribution of termite species and their respective feedings groups was determined by the habitat type and a set of environmental variables such as Woody Plant Diversity (WPD), Woody plant Families Diversity (WPFD), and Organic Carbon (OC). The annual Fire Occurrence (FO) was found to indirectly impact the characteristics of termite assemblages within natural habitats via their respective Herbaceous Species Richness (HSR) and Woody Plant Species Richness (WPSR). In summary, the spatial heterogeneity of the Comoe National Park, modeled by the uncontrolled annual bushfire, offers a diversified natural habitat with an important variety of termite-habitat-specific species, probably due to the food preference of these organisms and its relatively good conservation status.

Trophic level, successional age and trait matching determine specialization of deadwood-based interaction networks of saproxylic beetles.

The specialization of ecological networks provides important insights into possible consequences of biodiversity loss for ecosystem functioning. However, mostly mutualistic and antagonistic interactions of living organisms have been studied, whereas detritivore networks and their successional changes are largely unexplored. We studied the interactions of saproxylic (deadwood-dependent) beetles with their dead host trees. In a large-scale experiment, 764 logs of 13 tree species were exposed to analyse network structure of three trophic groups of saproxylic beetles over 3 successional years. We found remarkably high specialization of deadwood-feeding xylophages and lower specialization of fungivorous and predatory species. During deadwood succession, community composition, network specialization and network robustness changed differently for the functional groups. To reveal potential drivers of network specialization, we linked species' functional traits to their network roles, and tested for trait matching between plant (i.e. chemical compounds) and beetle (i.e. body size) traits. We found that both plant and animal traits are major drivers of species specialization, and that trait matching can be more important in explaining interactions than neutral processes reflecting species abundance distributions. High network specialization in the early successional stage and decreasing network robustness during succession indicate vulnerability of detritivore networks to reduced tree species diversity and beetle extinctions, with unknown consequences for wood decomposition and nutrient cycling.

Saving the injured: Rescue behavior in the termite-hunting ant Megaponera analis.

Predators of highly defensive prey likely develop cost-reducing adaptations. The ant Megaponera analis is a specialized termite predator, solely raiding termites of the subfamily Macrotermitinae (in this study, mostly colonies of Pseudocanthotermes sp.) at their foraging sites. The evolutionary arms race between termites and ants led to various defensive mechanisms in termites (for example, a caste specialized in fighting predators). Because M. analis incurs high injury/mortality risks when preying on termites, some risk-mitigating adaptations seem likely to have evolved. We show that a unique rescue behavior in M. analis, consisting of injured nestmates being carried back to the nest, reduces combat mortality. After a fight, injured ants are carried back by their nestmates; these ants have usually lost an extremity or have termites clinging to them and are able to recover within the nest. Injured ants that are forced experimentally to return without help, die in 32% of the cases. Behavioral experiments show that two compounds, dimethyl disulfide and dimethyl trisulfide, present in the mandibular gland reservoirs, trigger the rescue behavior. A model accounting for this rescue behavior identifies the drivers favoring its evolution and estimates that rescuing enables maintenance of a 28.7% larger colony size. Our results are the first to explore experimentally the adaptive value of this form of rescue behavior focused on injured nestmates in social insects and help us to identify evolutionary drivers responsible for this type of behavior to evolve in animals.

Diversity and Interactions of Wood-Inhabiting Fungi and Beetles after Deadwood Enrichment.

Freshly cut beech deadwood was enriched in the canopy and on the ground in three cultural landscapes in Germany (Swabian Alb, Hainich-Dün, Schorfheide-Chorin) in order to analyse the diversity, distribution and interaction of wood-inhabiting fungi and beetles. After two years of wood decay 83 MOTUs (Molecular Operational Taxonomic Units) from 28 wood samples were identified. Flight Interception Traps (FITs) installed adjacent to the deadwood enrichments captured 29.465 beetles which were sorted to 566 species. Geographical 'region' was the main factor determining both beetle and fungal assemblages. The proportions of species occurring in all regions were low. Statistic models suggest that assemblages of both taxa differed between stratum and management praxis but their strength varied among regions. Fungal assemblages in Hainich-Dün, for which the data was most comprehensive, discriminated unmanaged from extensively managed and age-class forests (even-aged timber management) while canopy communities differed not from those near the ground. In contrast, the beetle assemblages at the same sites showed the opposite pattern. We pursued an approach in the search for fungus-beetle associations by computing cross correlations and visualize significant links in a network graph. These correlations can be used to formulate hypotheses on mutualistic relationships for example in respect to beetles acting as vectors of fungal spores.

Land-use impacts on plant-pollinator networks: interaction strength and specialization predict pollinator declines.

Land use is known to reduce the diversity of species and complexity of biotic interactions. In theory, interaction networks can be used to predict the sensitivity of species against co-extinction, but this has rarely been applied to real ecosystems facing variable land-use impacts. We investigated plant-pollinator networks on 119 grasslands that varied quantitatively in management regime, yielding 25401 visits by 741 pollinator species on 166 plant species. Species-specific plant and pollinator responses to land use were significantly predicted by the weighted average land-use response of each species' partners. Moreover, more specialized pollinators were more vulnerable than generalists. Both predictions are based on the relative interaction strengths provided by the observed interaction network. Losses in flower and pollinator diversity were linked, and mutual dependence between plants and pollinators accelerates the observed parallel declines in response to land-use intensification. Our findings confirm that ecological networks help to predict natural community responses to disturbance and possible secondary extinctions.

Environmental factors affect Acidobacterial communities below the subgroup level in grassland and forest soils.

In soil, Acidobacteria constitute on average 20% of all bacteria, are highly diverse, and are physiologically active in situ. However, their individual functions and interactions with higher taxa in soil are still unknown. Here, potential effects of land use, soil properties, plant diversity, and soil nanofauna on acidobacterial community composition were studied by cultivation-independent methods in grassland and forest soils from three different regions in Germany. The analysis of 16S rRNA gene clone libraries representing all studied soils revealed that grassland soils were dominated by subgroup Gp6 and forest soils by subgroup Gp1 Acidobacteria. The analysis of a large number of sites (n = 57) by 16S rRNA gene fingerprinting methods (terminal restriction fragment length polymorphism [T-RFLP] and denaturing gradient gel electrophoresis [DGGE]) showed that Acidobacteria diversities differed between grassland and forest soils but also among the three different regions. Edaphic properties, such as pH, organic carbon, total nitrogen, C/N ratio, phosphorus, nitrate, ammonium, soil moisture, soil temperature, and soil respiration, had an impact on community composition as assessed by fingerprinting. However, interrelations with environmental parameters among subgroup terminal restriction fragments (T-RFs) differed significantly, e.g., different Gp1 T-RFs correlated positively or negatively with nitrogen content. Novel significant correlations of Acidobacteria subpopulations (i.e., individual populations within subgroups) with soil nanofauna and vascular plant diversity were revealed only by analysis of clone sequences. Thus, for detecting novel interrelations of environmental parameters with Acidobacteria, individual populations within subgroups have to be considered.

Seasonal dynamics of arboreal spider diversity in a temperate forest.

Measuring and estimating biodiversity patterns is a fundamental task of the scientist working to support conservation and inform management decisions. Most biodiversity studies in temperate regions were often carried out over a very short period of time (e.g., a single season) and it is often-at least tacitly-assumed that these short-term findings are representative of long-term general patterns. However, should the studied biodiversity pattern in fact contain significant temporal dynamics, perhaps leading to contradictory conclusions. Here, we studied the seasonal diversity dynamics of arboreal spider communities dwelling in 216 European beeches (Fagus sylvatica L.) to assess the spider community composition in the following seasons: two cold seasons (I: November 2005-January 2006; II: February-April) and two warm seasons (III: May-July; IV: August-October). We show that the usually measured diversity of the warm season community (IV: 58 estimated species) alone did not deliver a reliable image of the overall diversity present in these trees, and therefore, we recommend it should not be used for sampling protocols aimed at providing a full picture of a forest's biodiversity in the temperate zones. In particular, when the additional samplings of other seasons (I, II, III) were included, the estimated species richness nearly doubled (108). Community I possessed the lowest diversity and evenness due to the harsh winter conditions: this community was comprised of one dominant species together with several species low in abundance. Similarity was lowest (38.6%) between seasonal communities I and III, indicating a significant species turnover due to recolonization, so that community III had the highest diversity. Finally, using nonparametric estimators, we found that further sampling in late winter (February-April) is most needed to complete our inventory. Our study clearly demonstrates that seasonal dynamics of communities should be taken into account when studying biodiversity patterns of spiders, and probably forest arthropods in general.

Importance of protected areas for biodiversity conservation in central Côte D'ivoire: comparison of termite assemblages between two neighboring areas under differing levels of disturbance.

To highlight human impact on biodiversity in the Lamto region, termites were studied with regard to their use as bio-indicators of habitat change in the tropics. Using a standardized method, termites were sampled in the three most common habitat types, i.e., in semi-deciduous forest, savanna woodland, and annually burned savanna, all inside Lamto Reserve and its surrounding rural domain. Termite species richness fell from 25 species in the Lamto forest to 13 species in the rural area, involving strong modification in the species composition (species turnover = 59 %). In contrast, no significant change in diversity was found between the Lamto savannas and the rural ones. In addition, the relative abundance of termites showed a significantly greater decline in the rural domain, even in the species Ancistrotermes cavithorax (Sjöstedt) (Isoptera: Termitidae), which is known to be ecologically especially versatile. Overall, the findings of this study suggest further investigation around Lamto Reserve on the impact of human activities on biodiversity, focusing on forest conversion to land uses (e.g. agricultural and silvicultural systems).

Seed size selection by olive baboons.

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant's offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.

The causes of spatial patterning of mounds of a fungus-cultivating termite: results from nearest-neighbour analysis and ecological studies.

Little is known about processes regulating population dynamics in termites. We investigated the distribution of mound-colonies of the fungus-cultivating termite Macrotermes bellicosus (Smeathman) in two habitats in the Comoé National Park (Côte d'Ivoire) with nearest-neighbour analysis differentiating between different age classes. These results were compared with ecological data on processes influencing population dynamics. High mound densities were recorded in shrub savannah while only a few mounds were found in gallery forest. Mounds were distributed randomly in both habitats when all mounds were considered together, and when inhabited and uninhabited mounds were treated separately. However, distinctive non-random patterns were revealed in the savannah when we distinguished between different age classes. Small, young colonies were aggregated when they coexisted with larger, older colonies, which were more regularly distributed. This indicates that the distribution of older colonies is influenced by intraspecific competition whereas that of younger colonies is influenced by opposing factors that lead to aggregation. This is in accordance with ecological data. Food is a limiting resource for large colonies, while patchily distributed appropriate microclimatic conditions seem to be more important for young colonies. Colonies that had formerly coexisted (i.e. living colonies and recently dead colonies) showed aggregated, random and regular distribution patterns, suggesting several causes of mortality. Colonies that had never had contact with each other were randomly distributed and no specific regulation mechanism was implicated. These results show that different age classes seem to be regulated by different processes and that separation between age classes is necessary to reveal indicative spatial patterns in nearest-neighbour analysis.

Reproductive success of Macrotermes bellicosus (Isoptera, Macrotermitinae) in two neighbouring habitats.

The fungus-cultivating, mound-building termite Macrotermes bellicosus can reach high densities in African savannah habitats, whereas in forests it is comparatively rare and is only found in relatively open areas. Earlier studies in the Comoé National Park (Côte d'Ivoire, West Africa) suggested that this might be because ambient temperatures are lower in the forest than the savannah. Therefore, forests seem to be suboptimal habitats. During 3 consecutive years we measured relevant fitness parameters in both habitats to test this hypothesis. Colonies in the savannah had higher reproductive outputs. They reproduced annually, producing high numbers of offspring (alates), whereas forest colonies reproduced on average only once every 3 years and even then only low numbers of alates were produced. Annual growth of mound height, which can be regarded as an indicator of colony growth, varied considerably between individual colonies and years. Nevertheless, in two years the growth rate of mounds in the shrub savannah was higher than that of mounds in the gallery forest. Unexpectedly, survival probability as calculated by Kaplan Meier analysis was much lower for colonies in the shrub savannah than for colonies in the gallery forest. Using these data in a computer simulation we calculated lifetime reproductive success (LRS) for an average colony in both habitats. As LRS was much higher for colonies in the shrub savannah than in the gallery forest, these results confirmed our suggestion that the forest is a suboptimal habitat for M. bellicosus.