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The exploitation of landscapes increases fragmentation of valuable areas with high biodiversity. Consequently, many populations nowadays exist as metapopulations. In such cases, the balance between extinction and colonisation of patches determines the regional survival of species. To determine long term survival of species and to assess the impact of different management regimes proper knowledge of species habitat requirements as well as information on their dispersal behaviour is needed. The aim of this thesis was to develop methods and measures for the identification of suitable areas for grasshoppers and bush crickets, as well as to quantify the reachability of single patches by individuals. The first part of my work focuses on the quantification of habitat suitability for grasshoppers and bush crickets. Based on presence/absence data, I developed statistical habitat suitability models using logistic regression analyses. The resulting models are evaluated and validated in space and time. It turned out that habitat selection of the species mainly took place on an intermediate spatial scale. The relevant scale falls into the same range as the species’ mean dispersal distances. Besides the rather coarse grained factor ‘type of habitat’ structural factors as well as abiotic factors are correlated with the occurrence of the species. The model of S. lineatus, including the parameters ‘type of biotope’ and ‘vegetation height’ was most successful in predicting the occurrences of the bush cricket species. To further test whether the occurrence of species of different insect groups can be predicted with a common model, I tested the usefulness of the orthoptera models for the prediction of butterflies in the same region and vice versa. While transferability of the orthoptera models was poor, the model of the moth Z. carniolica performed quite successful. It included the proportion of suitable habitat as well as the occurrence of the two sucking plants C. jacea and S. columbaria as relevant factors. Z. carniolica is classified as stenoecious and thus represents other species typically found on fringes and mesoxerophytic grasslands. The high mobility of Z. carniolica simultaneously guarantees the reachability of regional suitable areas and thus ensures that the influence of the random effects of colonisation on the model are marginal. Unfortunately, the factors predicting habitat quality for a species are normally not available at the landscape level. Thus, they cannot be used for the prediction of occurrences without extensive censuses in the field. Nevertheless, my results show that the sole use of the variable ‘type of habitat’, which often is available landscape wide, will be sufficient for the classification of habitat suitability in a landscape. I conclude that for practical use in conservation biology the type of biotope can be used to predict occurrence of the studied species. Besides quality/quantity of suitable habitat, dispersal of individuals between patches is a key factor influencing the survival of populations. Thus, the second part of my work concentrates on theoretical as well as empirical studies on the dispersal behaviour of bush crickets. In field experiments I could show that the assumption of a dichotomous movement behaviour does not apply for bush crickets. Instead, movement pattern changes continuously with structural resistance, temperature, mortality risk and resource availability. This result is confirmed in my experiments on the behaviour of bush crickets at habitat borders. For different borders I could demonstrate different edge permeabilities. Additionally, I observed that grasshoppers could detect suitable habitat from a certain distance. Because the dispersal behaviour plays an important role in theoretical models, my empirical data can be used to parameterise such models. In addition to the influence of movement pattern on the reachability of suitable habitats, I could demonstrate, with simulation models, that the influence of the landscape context in which dispersal takes place has a critical impact on the exchange of individuals between patches. This effect is enhanced if mortality risk during dispersal is accounted for. The results from my studies on habitat suitability can be used to identify suitable habitat for grasshoppers and bush crickets in a landscape. Consequently, the potential suitability of an area as habitat, based on predictions on changes in the type of biotope by management regime, can be predicted. But this information alone is not sufficient to determine regional survival probability of a species. My investigations concerning the dispersal behaviour clearly show, that the reachability of suitable areas is dependent on the spatial configuration of patches and the structure of areas between habitats. Additionally, factors specific for individuals, like motivation and physiological factors play a crucial role for the reachability of suitable habitats.
The Mouthparts of Ants
(2001)
Ant mandible movements cover a wide range of forces, velocities and precision. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain how the attachment angles are optimized with respect to force and velocity output and how filament-attached fibers help to generate the largest force output from the available head capsule volume. In general, the entire mandible closer muscle is controlled by 10-12 motor neurons, some of which exclusively supply specific muscle fiber groups. Simultaneous recordings of muscle activity and mandible movement reveal that fast movements require rapid contractions of fast muscle fibers. Slow and accurate movements result from the activation of slow muscle fibers. Forceful movements are generated by simultaneous co-activation of all muscle fiber types. For fine control, distinct fiber bundles can be activated independently of each other. Retrograde tracing shows that most dendritic arborizations of the different sets of motor neurons share the same neuropil in the suboesophageal ganglion. In addition, some motor neurons invade specific parts of the neuropil. The labiomaxillary complex of ants is essential for food intake. I investigated the anatomical design of the labiomaxillary complex in various ant species focusing on movement mechanisms. The protraction of the glossa is a non muscular movement. Upon relaxation of the glossa retractor muscles, the glossa protracts elastically. I compared the design of the labiomaxillary complex of ants with that of the honey bee, and suggest an elastic mechanism for glossa protraction in honey bees as well. Ants employ two different techniques for liquid food intake, in which the glossa works either as a passive duct (sucking), or as an up- and downwards moving shovel (licking). For collecting fluids at ad libitum food sources, workers of a given species always use only one of both techniques. The species-specific feeding technique depends on the existence of a well developed crop and on the resulting mode of transporting the fluid food. In order to evaluate the performance of collecting liquids during foraging, I measured fluid intake rates of four ant species adapted to different ecological niches. Fluid intake rate depends on sugar concentration and the associated fluid viscosity, on the species-specific feeding technique, and on the extent of specialization on collecting liquid food. Furthermore, I compared the four ant species in terms of glossa surface characteristics and relative volumes of the muscles that control licking and sucking. Both probably reflect adaptations to the species-specific ecological niche and determine the physiological performance of liquid feeding. Despite species-specific differences, single components of the whole system are closely adjusted to each other according to a general rule.
Temporal development of communities with a focus on insects, in time series of one to four decades
(2021)
Changes and development are fundamental principles in biocenoses and can affect a multitude of ecological processes. In insect communities phenological and density changes, changes in species richness and community composition, as well as interactions between those changes, are the most important macro processes. However, climate change and other factors like habitat degradation and loss alter these processes leading to shifts and general biodiversity declines. Even though knowledge about insect decline in central Europe increased during the last decades, there are significant knowledge gaps about the development of insect communities in certain habitats and taxa. For example, insect communities in small lentic as well as in forested habitats are under-sampled and reported to be less endangered than communities in other habitats. Furthermore, the changes within habitats and taxa are additionally influenced by certain traits, like host or feeding specialization. To disentangle these influences and to increase the knowledge about the general long-term development of insect communities, comprehensive long-term monitoring studies are needed. In addition, long-term effects of conservation strategies should also be evaluated on large time scales in order to be able to decide on a scientific base which strategies are effective in promoting possibly declining taxa. Hence, this thesis also tackles the effects of an integrative conservation strategy on wood dependent beetle and fungi, beside the development of water beetle and macro moth communities over multiple decades. In Chapter 2 I present a study on the development of water beetle communities (Dytiscidae, Haliplidae, Noteridae) in 33 water bodies in Southern Germany from 1991 to 2018. Time-standardized capture per waterbody was used during three periods: between 1991 and 1995, 2007 and 2008, and 2017 and 2018. Results showed annual declines in both species number (ca. -1%) and abundance (ca. -2%). In addition, community composition shifted over time in part due to changing pH values. Hence, the recorded changes during the 28-year study period partly reflect natural succession processes. However, since also moor-related beetle species decreased significantly, it is likely that water beetles in southern Germany are also threatened by non-successional factors, including desiccation, increased nitrogen input and/or mineralization, as well as the loss of specific habitats. The results suggest, that in small to midsize lentic waterbodies, current development should aim for constant creation of new water bodies and protection of moor waterbodies in order to protect water beetle communities on a landscape scale. In Chapter 3 I present an analysis of the development of nocturnal macro moth species richness, abundance and biomass over four decades in forests of southern Germany. Two local scale data sets featuring a coppiced oak forest as well as an oak high forest were analysed separately from a regional data set representing all forest types in the temperate zone of Central Europe. At the regional scale species richness, abundance and biomass showed annual declines of ca. 1 %, 1.3 % and 1.4 %, respectively. These declines were more pronounced in plant host specialists and in dark coloured species. In contrast, species richness increased by ca. 1.5 % annually in the coppiced forest, while no significant trends were found in the high forest. In contrast to past assumptions, insect decline apparently affects also hyper diverse insect groups in forests. Since host specialists and dark coloured species were affected more heavily by the decline than other groups, habitat loss and climate change seem to be potential drivers of the observed trends. However, the positive development of species richness in the coppiced oak forest indicates that maintaining complex and diverse forest ecosystems through active management might compensate for negative trends in biodiversity. Chapter 4 features a study specifically aiming to investigate the long-term effect of deadwood enrichment as an integrative conservation strategy on saproxylic beetles and fungi in a central European beech forest at a landscape scale. A before–after control–impact design, was used to compare assemblages and gamma diversities of saproxylic organisms (beetles and fungi) in strictly protected old-growth forest areas (reserves) and previously moderately and intensively managed forest areas. Forests were sampled one year before and a decade after starting a landscape-wide strategy of dead-wood enrichment. Ten years after the start of the dead-wood enrichment, neither gamma diversities of saproxylic organisms nor species composition of beetles did reflect the previous management types anymore. However, fungal species composition still mirrored the previous management gradient. The results demonstrated that intentional enrichment of dead wood at the landscape scale can effectively restore communities of saproxylic organisms and may thus be a suitable strategy in addition to permanent strict reserves in order to protect wood dependent organisms in Europe. In this thesis I showed, that in contrast to what was assumed and partly reported so far, also water beetles in lentic water bodies and macro moths in forests decreased in species richness, abundance and biomass during the last three to four decades. In line with earlier studies, especially dark coloured species and specialists decreased more than light-coloured species and generalists. The reasons for these declines could partly be attributed to natural processes and pollution and possibly to climate change. However, further studies, especially experimental ones, will be needed to achieve a better understanding of the reasons for insect decline. Furthermore, analyses of time series data should be interpreted cautiously especially if the number of sampling years is smaller than ten years. In addition, validation techniques such as left- and right- censoring and cross validation should be used in order to proof the robustness of the analyses. However, the lack of knowledge, we are still facing today, should not prevent scientists and practitioners from applying conservation measures. In order to prove the effectiveness of such measures, long-term monitoring is crucial. Such control of success is essential for evidence based and thus adapted conservation strategies of threatened organisms.
Daily activities within an ant colony need precise temporal organization, and an endogenous clock appears to be essential for such timing processes. A clock drives locomotor rhythms in isolated workers in a number of ant species, but its involvement in activities displayed in the social context is unknown. We compared locomotor rhythms in isolated individuals and behavioral rhythms in the social context of workers of the ant Camponotus rufipes. Both forager and nurse workers exhibited circadian rhythms in locomotor activity under constant conditions, indicating the involvement of an endogenous clock. Activity was mostly nocturnal and synchronized with the 12:12h light-dark-cycle. To evaluate whether rhythmicity was maintained in the social context and could be synchronized with non-photic zeitgebers such as feeding times, daily behavioral activities of single workers inside and outside the nest were quantified continuously over 24 hours in 1656 hours of video recordings. Food availability was limited to a short time window either at day or at night, thus mimicking natural conditions of temporally restricted food access. Most foragers showed circadian foraging behavior synchronized with food availability, either at day or nighttime. When isolated thereafter in single locomotor activity monitors, foragers mainly displayed arrhythmicity. Here, high mortality suggested potential stressful effects of the former restriction of food availability. In contrast, nurse workers showed high overall activity levels in the social context and performed their tasks all around the clock with no circadian pattern, likely to meet the needs of the brood. In isolation, the same individuals exhibited in turn strong rhythmic activity and nocturnality. Thus, endogenous activity rhythms were inhibited in the social context, and timing of daily behaviors was flexibly adapted to cope with task demands. As a similar socially-mediated plasticity in circadian rhythms was already shown in honey bees, the temporal organization in C. rufipes and honey bees appear to share similar basic features.
Previous macroecological studies have suggested that larger and darker insects are favored in cold environments and that the importance of body size and color for the absorption of solar radiation is not limited to diurnal insects. However, whether these effects hold true for local communities and are consistent across taxonomic groups and sampling years remains unexplored. This study examined the variations in body size and color lightness of the two major families of nocturnal moths, Geometridae and Noctuidae, along an elevational gradient of 700 m in Southern Germany. An assemblage-based analysis was performed using community-weighted means and a fourth-corner analysis to test for variations in color and body size among communities as a function of elevation. This was followed by a species-level analysis to test whether species occurrence and abundance along an elevation gradient were related to these traits, after controlling for host plant availability. In both 2007 and 2016, noctuid moth assemblages became larger and darker with increasing elevation, whereas geometrids showed an opposite trend in terms of color lightness and no clear trend in body size. In single species models, the abundance of geometrids, but not of noctuids, was driven by habitat availability. In turn, the abundance of dark-colored noctuids, but not geometrids increased with elevation. While body size and color lightness affect insect physiology and the ability to cope with harsh conditions, divergent trait–environment relationships between both families underline that findings of coarse-scale studies are not necessarily transferable to finer scales. Local abundance and occurrence of noctuids are shaped by morphological traits, whereas that of geometrids are rather shaped by local habitat availability, which can modify their trait–environment-relationship. We discuss potential explanations such as taxon-specific flight characteristics and the effect of microclimatic conditions.
Planting non-native tree species, like Douglas fir in temperate European forest systems, is encouraged to mitigate effects of climate change. However, Douglas fir monocultures often revealed negative effects on forest biota, while effects of mixtures with native tree species on forest ecosystems are less well understood. We investigated effects of three tree species (Douglas fir, Norway spruce, native European beech), on ground beetles in temperate forests of Germany. Beetles were sampled in monocultures of each tree species and broadleaf-conifer mixtures with pitfall traps, and environmental variables were assessed around each trap. We used linear mixed models in a two-step procedure to disentangle effects of environment and tree species identity on ground beetle abundance, species richness, functional diversity and species assemblage structure. Contradictory to our expectations, ground beetle abundance and functional diversity was highest in pure Douglas fir stands, while tree mixtures showed intermediate values between pure coniferous and pure beech stands. The main drivers of these patterns were only partially dependent on tree species identity, which highlights the importance of structural features in forest stands. However, our study revealed distinct shifts in assemblage structure between pure beech and pure Douglas fir stands, which were only partially eased through mixture planting. Our findings suggest that effects of planting non-native trees on associated biodiversity can be actively modified by promoting beneficial forest structures. Nevertheless, integrating non-native tree species, even in mixtures with native trees, will invariably alter assemblage structures of associated biota, which can compromise conservation efforts targeted at typical species composition.
Bacterial symbionts of insects have received increasing attention due to their prominent role in nutrient acquisition and defense. In social bees, symbiotic bacteria can maintain colony homeostasis and fitness, and the loss or alteration of the bacterial community may be associated with the ongoing bee decline observed worldwide. However, analyses of microbiota associated with bees have been largely confined to the social honeybees (Apis mellifera) and bumblebees (Bombus spec.), revealing – among other taxa – host-specific lactic acid bacteria (LAB, genus Lactobacillus) that are not found in solitary bees. Here, we characterized the microbiota of three Australian stingless bee species (Apidae: Meliponini) of two phylogenetically distant genera (Tetragonula and Austroplebeia). Besides common plant bacteria, we find LAB in all three species, showing that LAB are shared by honeybees, bumblebees and stingless bees across geographical regions. However, while LAB of the honeybee-associated Firm4–5 clusters were present in Tetragonula, they were lacking in Austroplebeia. Instead, we found a novel clade of likely host-specific LAB in all three Australian stingless bee species which forms a sister clade to a large cluster of Halictidae-associated lactobacilli. Our findings indicate both a phylogenetic and geographical signal of host-specific LAB in stingless bees and highlight stingless bees as an interesting group to investigate the evolutionary history of the bee-LAB association.
Tropical mountain forests contribute disproportionately to terrestrial biodiversity but little is known about insect diversity in the canopy and how it is distributed between tree species. We sampled tree-specific arthropod communities from 28 trees by canopy fogging and analysed beetle communities which were first morphotyped and then identified by their DNA barcodes. Our results show that communities from forests at 1100 and 1700 m a.s.l. are almost completely distinct. Diversity was much lower in the upper forest while community structure changed from many rare, less abundant species to communities with a pronounced dominance structure. We also found significantly higher beta-diversity between trees at the lower than higher elevation forest where community similarity was high. Comparisons on tree species found at both elevations reinforced these results. There was little species overlap between sites indicating limited elevational ranges. Furthermore, we exploited the advantage of DNA barcodes to patterns of haplotype diversity in some of the commoner species. Our results support the advantage of fogging and DNA barcodes for community studies and underline the need for comprehensive research aimed at the preservation of these last remaining pristine forests.
Mimicking female insects to attract male pollinators is an important strategy in sexually deceptive orchids of the genus Ophrys, and some species possess flowers with conspicuous labellum patterns. The function of the variation of the patterns remains unresolved, with suggestions that these enhance pollinator communication. We investigated the possible function of the labellum pattern in Ophrys heldreichii, an orchid species in which the conspicuous and complex labellum pattern contrasts with a dark background. The orchid is pollinated exclusively by males of the solitary bee, Eucera berlandi. Comparisons of labellum patterns revealed that patterns within inflorescences are more similar than those of other conspecific plants. Field observations showed that the males approach at a great speed and directly land on flowers, but after an unsuccessful copulation attempt, bees hover close and visually scan the labellum pattern for up to a minute. Learning experiments conducted with honeybees as an accessible model of bee vision demonstrated that labellum patterns of different plants can be reliably learnt; in contrast, patterns of flowers from the same inflorescence could not be discriminated. These results support the hypothesis that variable labellum patterns in O. heldreichii are involved in flower-pollinator communication which would likely help these plants to avoid geitonogamy.
Quantitative information is omnipresent in the world and a wide range of species has been shown to use quantities to optimize their decisions. While most studies have focused on vertebrates, a growing body of research demonstrates that also insects such as honeybees possess basic quantitative abilities that might aid them in finding profitable flower patches. However, it remains unclear if for insects, quantity is a salient feature relative to other stimulus dimensions, or if it is only used as a “last resort” strategy in case other stimulus dimensions are inconclusive. Here, we tested the stingless bee Trigona fuscipennis, a species representative of a vastly understudied group of tropical pollinators, in a quantity discrimination task. In four experiments, we trained wild, free-flying bees on stimuli that depicted either one or four elements. Subsequently, bees were confronted with a choice between stimuli that matched the training stimulus either in terms of quantity or another stimulus dimension. We found that bees were able to discriminate between the two quantities, but performance differed depending on which quantity was rewarded. Furthermore, quantity was more salient than was shape. However, quantity did not measurably influence the bees' decisions when contrasted with color or surface area. Our results demonstrate that just as honeybees, small-brained stingless bees also possess basic quantitative abilities. Moreover, invertebrate pollinators seem to utilize quantity not only as "last resort" but as a salient stimulus dimension. Our study contributes to the growing body of knowledge on quantitative cognition in invertebrate species and adds to our understanding of the evolution of numerical cognition.