590 Tiere (Zoologie)
Refine
Has Fulltext
- yes (137)
Is part of the Bibliography
- yes (137)
Year of publication
Document Type
- Journal article (78)
- Doctoral Thesis (47)
- Book article / Book chapter (4)
- Book (3)
- Conference Proceeding (3)
- Master Thesis (1)
- Review (1)
Language
- English (98)
- German (37)
- Multiple languages (2)
Keywords
- Biene (11)
- Ameisen (7)
- Biologie (6)
- Verhalten (5)
- Zoologie (5)
- bees (5)
- Apis mellifera (4)
- ants (4)
- climate change (4)
- foraging (4)
Institute
Sonstige beteiligte Institutionen
EU-Project number / Contract (GA) number
- 244090 (2)
- LIFE12 BIO/AT/000143 (1)
- LIFE20 NAT/AT/000049 (1)
Although much is known about the ecology and functional importance of canopy arthropods in temperate forests, few studies have tried to assess the overall diversity and investigate the composition and dynamics of tree-specific communities. This has impeded a deeper understanding of the functioning of forests, and of how to maintain system services. Here, we present the first comprehensive data of whole arthropod communities, collected by insecticidal knockdown (fogging) from 1159 trees in 18 study areas in Central Europe during the last 25 years. The data includes 3,253,591 arthropods from 32 taxa (order, suborder, family) collected on 24 tree species from 18 genera. Fogging collects free-living, ectophytic arthropods in approximately the same number as they occur in the trees. To our knowledge, these are the most comprehensive data available today on the taxonomic composition of arboreal fauna. Assigning all arthropods to their feeding guild provided a proxy of their functional importance. The data showed that the canopy communities were regularly structured, with a clear dominance hierarchy comprised of eight ‘major taxa’ that represented 87% of all arthropods. Despite significant differences in the proportions of taxa on deciduous and coniferous trees, the composition of the guilds was very similar. The individual tree genera, on the other hand, showed significant differences in guild composition, especially when different study areas and years were compared, whereas tree-specific traits, such as tree height, girth in breast height or leaf cover, explained little of the overall variance. On the ordinal level, guild composition also differed significantly between managed and primary forests, with a simultaneous low within-group variability, indicating that management is a key factor determining the distribution of biodiversity and guild composition.
In the eusocial insect honeybee (Apis mellifera), many sterile worker bees live together with a reproductive queen in a colony. All tasks of the colony are performed by the workers, undergoing age-dependent division of labor. Beginning as hive bees, they take on tasks inside the hive such as cleaning or the producing of larval food, later developing into foragers. With that, the perception of sweetness plays a crucial role for all honeybees whether they are sitting on the honey stores in the hive or foraging for food. Their ability to sense sweetness is undoubtedly necessary to develop and evaluate food sources. Many of the behavioral decisions in honeybees are based on sugar perception, either on an individual level for ingestion, or for social behavior such as the impulse to collect or process nectar. In this context, honeybees show a complex spectrum of abilities to perceive sweetness on many levels. They are able to perceive at least seven types of sugars and decide to collect them for the colony. Further, they seem to distinguish between these sugars or at least show clear preferences when collecting them. Additionally, the perception of sugar is not rigid in honeybees. For instance, their responsiveness towards sugar changes during the transition from in-hive bees (e.g. nurses) to foraging and is linked to the division of labor. Other direct or immediate factors changing responsiveness to sugars are stress, starvation or underlying factors, such as genotype.
Interestingly, the complexity in their sugar perception is in stark contrast to the fact that honeybees seem to have only three predicted sugar receptors.
In this work, we were able to characterize the three known sugar receptors (AmGr1, AmGr2 and AmGr3) of the honeybee fully and comprehensively in oocytes (Manuscript II, Chapter 3 and Manuscript III, Chapter 4). We could show that AmGr1 is a broad sugar receptor reacting to sucrose, glucose, maltose, melezitose and trehalose (which is the honeybees’ main blood sugar), but not fructose. AmGr2 acts as its co-receptor altering AmGr1’s specificity, AmGr3 is a specific fructose receptor and we proved the heterodimerization of all receptors. With my studies, I was able to reproduce and compare the ligand specificity of the sugar receptors in vivo by generating receptor mutants with CRISPR/Cas9. With this thesis, I was able to define AmGr1 and AmGr3 as the honeybees’ basis receptors already capable to detect all sugars of its known taste spectrum.
In the expression analysis of my doctoral thesis (Manuscript I, Chapter 2) I demonstrated that both basis receptors are expressed in the antennae and the brain of nurse bees and foragers. This thesis assumes that AmGr3 (like the Drosophila homologue) functions as a sensor for fructose, which might be the satiety signal, while AmGr1 can sense trehalose as the main blood sugar in the brain. Both receptors show a reduced expression in the brain of foragers when compared with nurse bees. These results may reflect the higher concentrated diet of nurse bees in the hive. The higher number of receptors in the brain may allow nurse bees to perceive hunger earlier and to consume the food their sitting on. Forager bees have to be more persistent to hunger, when they are foraging, and food is not so accessible. The findings of reduced expression of the fructose receptor AmGr3 in the antennae of nurse bees are congruent with my other result that nurse bees are also less responsive to fructose at the antennae when compared to foragers (Manuscript I, Chapter 2). This is possible, since nurse bees sit more likely on ripe honey which contains not only higher levels of sugars but also monosaccharides (such as fructose), while foragers have to evaluate less-concentrated nectar.
My investigations of the expression of AmGr1 in the antennae of honeybees found no differences between nurse bees and foragers, although foragers are more responsive to the respective sugar sucrose (Manuscript I, Chapter 2). Considering my finding that AmGr2 is the co-receptor of AmGr1, it can be assumed that AmGr1 and the mediated sucrose taste might not be directly controlled by its expression, but indirectly by its co-receptor. My thesis therefore clearly shows that sugar perception is associated with division of labor in honeybees and appears to be directly or indirectly regulated via expression.
The comparison with a characterization study using other bee breeds and thus an alternative protein sequence of AmGr1 shows that co-expression of different AmGr1 versions with AmGr2 alters the sugar response differently. Therefore, this thesis provides first important indications that alternative splicing could also represent an important regulatory mechanism for sugar perception in honeybees.
Further, I found out that the bitter compound quinine lowers the reward quality in learning experiments for honeybees (Manuscript IV, Chapter 5). So far, no bitter receptor has been found in the genome of honeybees and this thesis strongly assumes that bitter substances such as quinine inhibit sugar receptors in honeybees. With this finding, my work includes other molecules as possible regulatory mechanism in the honeybee sugar perception as well. We showed that the inhibitory effect is lower for fructose compared to sucrose. Considering that sugar signals might be processed as differently attractive in honeybees, this thesis concludes that the sugar receptor inhibition via quinine in honeybees might depend on the receptor (or its co-receptor), is concentration-dependent and based on the salience or attractiveness and concentration of the sugar present.
With my thesis, I was able to expand the knowledge on honeybee’s sugar perception and formulate a complex, comprehensive overview. Thereby, I demonstrated the multidimensional mechanism that regulates the sugar receptors and thus the sugar perception of honeybees. With this work, I defined AmGr1 and AmGr3 as the basis of sugar perception and enlarged these components to the co-receptor AmGr2 and the possible splice variants of AmGr1. I further demonstrated how those sugar receptor components function, interact and that they are clearly involved in the division of labor in honeybees. In summary, my thesis describes the mechanisms that enable honeybees to perceive sugar in a complex way, even though they inhere a limited number of sugar receptors. My data strongly suggest that honeybees overall might not only differentiate sugars and their diet by their general sweetness (as expected with only one main sugar receptor). The found sugar receptor mechanisms and their interplay further suggest that honeybees might be able to discriminate directly between monosaccharides and disaccharides or sugar molecules and with that their diet (honey and nectar).
The Northern Bald Ibis (Geronticus eremita, NBI) is an endangered migratory species, which went extinct in Europe in the 17th century. Currently, a translocation project in the frame of the European LIFE program is carried out, to reintroduce a migratory population with breeding colonies in the northern and southern Alpine foothills and a common wintering area in southern Tuscany. The population meanwhile consists of about 200 individuals, with about 90% of them carrying a GPS device on their back. We used biologging data from 2021 to model the habitat suitability for the species in the northern Alpine foothills. To set up a species distribution model, indices describing environmental conditions were calculated from satellite images of Landsat-8, and in addition to the well-proven use of optical remote sensing data, we also included Sentinel-1 actively sensed observation data, as well as climate and urbanization data. A random forest model was fitted on NBI GPS positions, which we used to identify regions with high predicted foraging suitability within the northern Alpine foothills. The model resulted in 84.5% overall accuracy. Elevation and slope had the highest predictive power, followed by grass cover and VV intensity of Sentinel-1 radar data. The map resulting from the model predicts the highest foraging suitability for valley floors, especially of Inn, Rhine, and Salzach-Valley as well as flatlands, like the Swiss Plateau and the agricultural areas surrounding Lake Constance. Areas with a high suitability index largely overlap with known historic breeding sites. This is particularly noteworthy because the model only refers to foraging habitats without considering the availability of suitable breeding cliffs. Detailed analyses identify the transition zone from extensive grassland management to intensive arable farming as the northern range limit. The modeling outcome allows for defining suitable areas for further translocation and management measures in the frame of the European NBI reintroduction program. Although required in the international IUCN translocation guidelines, the use of models in the context of translocation projects is still not common and in the case of the Northern Bald Ibis not considered in the present Single Species Action Plan of the African-Eurasian Migratory Water bird Agreement. Our species distribution model represents a contemporary snapshot, but sustainability is essential for conservation planning, especially in times of climate change. In this regard, a further model could be optimized by investigating sustainable land use, temporal dynamics, and climate change scenarios.
Coral reefs are one of the most diverse marine ecosystems, providing numerous ecosystem services. This present study investigated the relationship between coral reef condition and the diversity and abundance of fishes, on a heavily fished East African coral reef at Gazi Bay, Kenya. Underwater visual censuses were conducted on thirty 50 × 5 m belt transects to assess the abundance and diversity of fishes. In parallel, a 25-m length of each of the same transects was recorded with photo-quadrats to assess coral community structure and benthic characteristics. For statistical analyses, multi-model inference based on the Akaike Information Criterion was used to evaluate the support for potential predictor variables of coral reef and fish diversity. We found that coral genus richness was negatively correlated with the abundance of macroalgae, whereas coral cover was positively correlated with both the abundance of herbivorous invertebrates (sea urchins) and with fish family richness. Similarly, fish family richness appeared mainly correlated with coral cover and invertebrate abundance, although no correlates of fish abundance could be identified. Coral and fish diversity were very low, but it appears that, contrary to some locations on the same coast, sea urchin abundance was not high enough to be having a negative influence on coral and fish assemblages. Due to increasing threats to coral reefs, it is important to understand the relationship among the components of the coral reef ecosystem on overfished reefs such as that at Gazi Bay.
Monarch butterflies are famous for their annual long-distance migration. Decreasing temperatures and reduced daylight induce the migratory state in the autumn generation of monarch butterflies. Not only are they in a reproductive diapause, they also produce fat deposits to be prepared for the upcoming journey: Driven by their instinct to migrate, they depart from their eclosion grounds in the northern regions of the North American continent and start their southern journey to their hibernation spots in Central Mexico. The butterflies cover a distance of up to 4000 km across the United States. In the next spring, the same butterflies invert their preferred heading direction due to seasonal changes and start their northward spring migration. The spring migration is continued by three consecutive butterfly generations, until the animals repopulate the northern regions in North America as non-migratory monarch butterflies. The monarch butterflies’ migratory state is genetically and epigenetically regulated, including the directed flight behavior. Therefore, the insect’s internal compass system does not only have to encode the butterflies preferred, but also its current heading direction. However, the butterfly’s internal heading representation has to be matched to external cues, to avoid departing from its initial flight path and increasing its risk of missing its desired destination. During the migratory flight, visual cues provide the butterflies with reliable orientation information. The butterflies refer to the sun as their main orientation cue. In addition to the sun, the butterflies likely use the polarization pattern of the sky for orientation. The sky compass signals are processed within a region in the brain, termed the central complex (CX). Previous research on the CX neural circuitry of the monarch butterflies demonstrated that tangential central complex neurons (TL) carry the visual input information into the CX and respond to a simulated sun and polarized light. However, whether these cells process additional visual cues like the panoramic skyline is still unknown. Furthermore, little is known about how the migratory state affects visual cue processing. In addition to this, most experiments studying the monarch butterfly CX focused on how neurons process single visual cues. However, how combined visual stimuli are processed in the CX is still unknown.
This thesis is investigating the following questions:
1) How does the migratory state affect visual cue processing in the TL cells within the monarch butterfly brain?
2) How are multiple visual cues integrated in the TL cells?
3) How is compass information modulated in the CX?
To study these questions, TL neurons from both animal groups (migratory and non-migratory) were electrophysiologically characterized using intracellular recordings while presenting different simulated celestial cues and visual sceneries. I showed that the TL neurons of migratory butterflies are more narrowly tuned to the sun, possibly helping them in keeping a directed flight course during migration. Furthermore, I found that TL cells encode a panoramic skyline, suggesting that the CX network combines celestial and terrestrial information. Experiments with combined celestial stimuli revealed that the TL cells combine both cue information linearly. However, if exposing the animals to a simulated visual scenery containing a panoramic skyline and a simulated sun, the single visual cues are weighted differently. These results indicate that the CX’s input region can flexibly adapt to different visual cue conditions. Furthermore, I characterize a previously unknown neuron in the monarch butterfly CX which responds to celestial stimuli and connects the CX with other brain neuropiles. How this cell type affects heading direction encoding has yet to be determined.
Monarch butterflies rely on external cues for orientation during their annual long-distance migration from Northern US and Canada to Central Mexico. These external cues can be celestial cues, such as the sun or polarized light, which are processed in a brain region termed the central complex (CX). Previous research typically focused on how individual simulated celestial cues are encoded in the butterfly's CX. However, in nature, the butterflies perceive several celestial cues at the same time and need to integrate them to effectively use the compound of all cues for orientation. In addition, a recent behavioral study revealed that monarch butterflies can rely on terrestrial cues, such as the panoramic skyline, for orientation and use them in combination with the sun to maintain a directed flight course. How the CX encodes a combination of celestial and terrestrial cues and how they are weighted in the butterfly's CX is still unknown. Here, we examined how input neurons of the CX, termed TL neurons, combine celestial and terrestrial information. While recording intracellularly from the neurons, we presented a sun stimulus and polarized light to the butterflies as well as a simulated sun and a panoramic scene simultaneously. Our results show that celestial cues are integrated linearly in these cells, while the combination of the sun and a panoramic skyline did not always follow a linear integration of action potential rates. Interestingly, while the sun and polarized light were invariantly weighted between individual neurons, the sun stimulus and panoramic skyline were dynamically weighted when both stimuli were simultaneously presented. Taken together, this dynamic weighting between celestial and terrestrial cues may allow the butterflies to flexibly set their cue preference during navigation.
The original habitat of native European honey bees (\(Apis\) \(mellifera\)) is forest, but currently there is a lack of data about the occurrence of wild honey bee populations in Europe. Prior to being kept by humans in hives, honey bees nested as wild species in hollow trees in temperate forests. However, in the 20th century, intensification of silviculture and agriculture with accompanying losses of nesting sites and depletion of food resources caused population declines in Europe. When the varroa mite (Varroa destructor), an invasive ectoparasite from Asia, was introduced in the late 1970s, wild honey bees were thought to be eradicated in Europe. Nevertheless, sporadic, mostly anecdotal, reports from ornithologists or forest ecologists indicated that honey bee colonies still occupy European forest areas. In my thesis I hypothesize that near-natural deciduous forests may provide sufficient large networks of nesting sites representing refugia for wild-living honey bees. Using two special search techniques, i.e. the tracking of flight routes of honey bee foragers (the “beelining” method) and the inspection of known cavity trees, I collected for the first time data on the occurrence and density of wild-living honey bees in forest areas in Germany (CHAPTER 3). I found wild-living honey bee colonies in the Hainich national park at low densities in two succeeding years. In another forest region, I checked known habitat trees containing black woodpecker cavities for occupation by wild-living honey bee colonies. It turned out that honey bees regularly use these cavities and occur in similar densities in both studied forest regions, independent of the applied detection method. Extrapolating these densities to all German forest areas, I estimate several thousand wild-living colonies in Germany that potentially interact in different ways with the forest environment. I conclude that honey bees regularly colonize forest areas in Germany and that networks of mapped woodpecker cavities offer unique possibilities to study the ecology of wild-living honey bees over several years.
While their population status is ambiguous and the density of colonies low, the fact that honey bees can still be found in forests poses questions about food supply in forest environments. Consequently, I investigated the suitability of woodlands as a honey bee foraging habitat (CHAPTER 4). As their native habitat, forests are assumed to provide important pollen and nectar sources for honey bee colonies. However, resource supply might be spatially and temporally restricted and landscape-scale studies in European forest regions are lacking. Therefore, I set up twelve honey bee colonies in observation hives at locations with varying degree of forest cover. Capitalizing on the unique communication behaviour, the waggle dance, I examined the foraging distances and habitat preferences of honey bees over almost an entire foraging season. Moreover, by connecting this decoded dance information with colony weight recordings, I could draw conclusions about the contribution of the different habitat types to honey yield. Foraging distances generally increased with the amount of forest in the surrounding landscape. Yet, forest cover did not have an effect on colony weight. Compared to expectations based on the proportions of different habitats in the surroundings, colonies foraged more frequently in cropland and grasslands than in deciduous and coniferous forests, especially in late summer when pollen foraging in the forest is most difficult. In contrast, colonies used forests for nectar/honeydew foraging in early summer during times of colony weight gain emphasizing forests as a temporarily significant source of carbohydrates. Importantly, my study shows that the ecological and economic value of managed forest as habitat for honey bees and other wild pollinators can be significantly increased by the continuous provision of floral resources, especially for pollen foraging.
The density of these wild-living honey bee colonies and their survival is driven by several factors that vary locally, making it crucial to compare results in different regions. Therefore, I investigated a wild-living honey bee population in Galicia in north-western Spain, where colonies were observed to reside in hollow electric poles (CHAPTER 5). The observed colony density only in these poles was almost twice as high as in German forest areas, suggesting generally more suitable resource conditions for the bees in Galicia. Based on morphometric analyses of their wing venation patterns, I assigned the colonies to the native evolutionary lineage (M-lineage) where the particularly threatened subspecies \(Apis\) \(mellifera\) \(iberiensis\) also belongs to. Averaged over two consecutive years, almost half of the colonies survived winter (23 out of 52). Interestingly, semi-natural areas both increased abundance and subsequent colony survival. Colonies surrounded by more semi-natural habitat (and therefore less intensive cropland) had an elevated overwintering probability, indicating that colonies need a certain amount of semi-natural habitat in the landscape to survive. Due to their ease of access these power poles in Galicia are, ideally suited to assess the population demography of wild-living Galician honey bee colonies through a long-term monitoring.
In a nutshell, my thesis indicates that honey bees in Europe always existed in the wild. I performed the first survey of wild-living bee density yet done in Germany and Spain. My thesis identifies the landscape as a major factor that compromises winter survival and reports the first data on overwintering rates of wild-living honey bees in Europe. Besides, I established methods to efficiently detect wild-living honey bees in different habitat. While colonies can be found all over Europe, their survival and viability depend on unpolluted, flower rich habitats. The protection of near-natural habitat and of nesting sites is of paramount importance for the conservation of wild-living honey bees in Europe.
The monitoring of species and functional diversity is of increasing relevance for the development of strategies for the conservation and management of biodiversity. Therefore, reliable estimates of the performance of monitoring techniques across taxa become important. Using a unique dataset, this study investigates the potential of airborne LiDAR-derived variables characterizing vegetation structure as predictors for animal species richness at the southern slopes of Mount Kilimanjaro. To disentangle the structural LiDAR information from co-factors related to elevational vegetation zones, LiDAR-based models were compared to the predictive power of elevation models. 17 taxa and 4 feeding guilds were modeled and the standardized study design allowed for a comparison across the assemblages. Results show that most taxa (14) and feeding guilds (3) can be predicted best by elevation with normalized RMSE values but only for three of those taxa and two of those feeding guilds the difference to other models is significant. Generally, modeling performances between different models vary only slightly for each assemblage. For the remaining, structural information at most showed little additional contribution to the performance. In summary, LiDAR observations can be used for animal species prediction. However, the effort and cost of aerial surveys are not always in proportion with the prediction quality, especially when the species distribution follows zonal patterns, and elevation information yields similar results.
Humans and animals alike use the sun, the moon, and the stars to guide their ways.
However, the position of celestial cues changes depending on daytime, season, and
place on earth. To use these celestial cues for reliable navigation, the rotation of the
sky has to be compensated. While humans invented complicated mechanisms like the
Antikythera mechanism to keep track of celestial movements, animals can only rely on
their brains. The desert ant Cataglyphis is a prime example of an animal using celestial
cues for navigation. Using the sun and the related skylight polarization pattern as a
compass, and a step integrator for distance measurements, it can determine a vector
always pointing homewards. This mechanism is called path integration. Since the sun’s
position and, therefore, also the polarization pattern changes throughout the day,
Cataglyphis have to correct this movement. If they did not compensate for time, the
ants’ compass would direct them in different directions in the morning and the evening.
Thus, the ants have to learn the solar ephemeris before their far-reaching foraging
trips.
To do so, Cataglyphis ants perform a well-structured learning-walk behavior during the
transition phase from indoor worker to outdoor forager. While walking in small loops
around the nest entrance, the ants repeatedly stop their forward movements to perform
turns. These can be small walked circles (voltes) or tight turns about the ants’ body
axes (pirouettes). During pirouettes, the ants gaze back to their nest entrance during
stopping phases. These look backs provide a behavioral read-out for the state of the
path integrator. The ants “tell” the observer where they think their nest is, by looking
back to it. Pirouettes are only performed by Cataglyphis ants inhabiting an environment
with a prominent visual panorama. This indicates, that pirouettes are performed to
learn the visual panorama. Voltes, on the other hand, might be used for calibrating the
celestial compass of the ants.
In my doctoral thesis, I employed a wide range of state-of-the-art techniques from
different disciplines in biology to gain a deeper understanding of how navigational
information is acquired, memorized, used, and calibrated during the transition phase
from interior worker to outdoor forager. I could show, that celestial orientation cues that
provide the main compass during foraging, do not guide the ants during the look-backbehavior
of initial learning walks. Instead Cataglyphis nodus relies on the earth’s
magnetic field as a compass during this early learning phase. While not guiding the
ants during their first walks outside of the nest, excluding the ants from perceiving the
natural polarization pattern of the skylight has significant consequences on learning-related
plasticity in the ants’ brain. Only if the ants are able to perform their learning-walk
behavior under a skylight polarization pattern that changes throughout the day,
plastic neuronal changes in high-order integration centers are induced. Especially the
mushroom bogy collar, a center for learning and memory, and the central complex, a
center for orientation and motor control, showed an increase in volume after learning
walks. This underlines the importance of learning walks for calibrating the celestial
compass. The magnetic compass might provide the necessary stable reference
system for the ants to calibrate their celestial compass and learn the position of
landmark information. In the ant brain, visual information from the polarization-sensitive
ocelli converge in tight apposition with neuronal afferents of the mechanosensitive
Johnston’s organ in the ant’s antennae. This makes the ants’ antennae an interesting
candidate for studying the sensory bases of compass calibration in Cataglyphis ants.
The brain of the desert navigators is well adapted to successfully accomplish their
navigational needs. Females (gynes and workers) have voluminous mushroom bodies,
and the synaptic complexity to store large amount of view-based navigational
information, which they acquire during initial learning walks. The male Cataglyphis
brain is better suited for innate behaviors that support finding a mate.
The results of my thesis show that the well adapted brain of C. nodus ants undergoes
massive structural changes during leaning walks, dependent on a changing celestial
polarization pattern. This underlies the essential role of learning walks in the calibration
of orientation systems in desert ants.
Chapter 1 – General introduction
Anthropogenic land-use and climate change are the major drivers of the global biodiversity loss. Yet, biodiversity is essential for human well-being, as we depend on the availability of potable water, sufficient food and further benefits obtained from nature. Each species makes a somewhat unique contribution to these ecosystem services. Furthermore, species tolerate environmental stressors, such as climate change, differently. Thus, biodiversity is both the "engine" and the "insurance" for human well-being in a changing climate. Here, I investigate the effects of temperature and land use on herbivory (Chapter 2), predation (Chapter 3) and pest control (Chapter 4), and at the same time identify features of habitats (e.g. plant richness, proximity to different habitat types) and landscapes (e.g. landscape diversity, proportion of oilseed rape area) as potential management targets in an adaptation strategy to climate change. Finally, I discuss the similarities and differences between factors influencing herbivory, predation and pest control, while placing the observations in the context of climate change as a multifaceted phenomenon, and highlighting starting points for sustainable insect pest management (Chapter 5).
Chapter 2 – Plant richness, land use and temperature differently shape invertebrate leaf-chewing herbivory on major plant functional groups
Invertebrate herbivores are temperature-sensitive. Rising temperatures increase their metabolic rates and thus their demand for carbon-rich relative to protein-rich resources, which can lead to changes in the diets of generalist herbivores. Here, we quantified leaf-area loss to chewing invertebrates among three plant functional groups (legumes, non-leguminous forbs and grasses), which largely differ in C:N (carbon:nitrogen) ratio. This reseach was conducted along spatial temperature and land-use gradients in open herbaceous vegetation adjacent to different habitat types (forest, grassland, arable field, settlement). Herbivory largely differed among plant functional groups and was higher on legumes than forbs and grasses, except in open areas in forests. There, herbivory was similar among plant functional groups and on legumes lower than in grasslands. Also the presence of many plant families lowered herbivory on legumes. This suggests that open areas in forests and diverse vegetation provide certain protection against leaf damage to some plant families (e.g. legumes). This could be used as part of a conservation strategy for protected species. Overall, the effects of the dominant habitat type in the vicinity and diverse vegetation outweighed those of temperature and large-scale land use (e.g. grassland proportion, landscape diversity) on herbivory of legumes, forbs and grasses at the present time.
Chapter 3 – Landscape diversity and local temperature, but not climate, affect arthropod predation among habitat types
Herbivorous insects underlie top-down regulation by arthropod predators. Thereby, predation rates depend on predator community composition and behaviour, which is shaped by temperature, plant richness and land use. How the interaction of these factors affects the regulatory performance of predators was unknown. Therefore, we assessed arthropod predation rates on artificial caterpillars along temperature, and land-use gradients. On plots with low local mean temperature (≤ 7°C) often not a single caterpillar was attacked, which may be due to the temperature-dependent inactivity of arthropods. However, multi-annual mean temperature, plant richness and the dominant habitat type in the vicinity did not substantially affect arthropod predation rates. Highest arthropod predation rates were observed in diverse landscapes (2-km scale) independently of the locally dominanting habitat type. As landscape diversity, but not multi-annual mean temperature, affected arthropod predation rates, the diversification of landscapes may also support top-down regulation of herbivores independent of moderate increases of multi-annual mean temperature in the near future.
Chapter 4 – Pest control and yield of winter oilseed rape depend on spatiotemporal crop-cover dynamics and flowering onset: implications for global warming
Winter oilseed rape is an important oilseed crop in Europe, yet its seed yield is diminished through pests such as the pollen beetle and stem weevils. Damage from pollen beetles depends on pest abundances, but also on the timing of infestation relative to crop development as the bud stage is particularly vulnerable. The development of both oilseed rape and pollen beetles is temperature-dependent, while temperature effects on pest abundances are yet unknown, which brings opportunities and dangers to oilseed rape cropping under increased temperatures. We obtained measures of winter oilseed rape (flowering time, seed yield) and two of its major pests (pollen beetle, stem weevils) for the first time along both land-use and temperature gradients. Infestation with stem weevils was not influenced by any temperature or land-use aspect considered, and natural pest regulation of pollen beetles in terms of parasitism rates of pollen beetle larvae was low (< 30%), except on three out of 29 plots. Nonetheless, we could identify conditions favouring low pollen beetle abundances per plant and high seed yields. Low pollen beetle densities were favoured by a constant oilseed rape area relative to the preceding year (5-km scale), whereas a strong reduction in area (> 40%) caused high pest densities (concentration effect). This occurred more frequently in warmer regions, due to drought around sowing, which contributed to increased pollen beetle numbers in those regions. Yet, in warmer regions, oilseed rape flowered early, which possibly led to partial escape from pollen beetle infestation in the most vulnerable bud stage. This is also suggested by higher seed yields of early flowering oilseed rape fields, but not per se at higher temperatures. Thus, early flowering (e.g. cultivar selection) and the interannual coordination of oilseed rape area offer opportunities for environmental-friendly pollen beetle management.
Chapter 5 – General discussion
Anthropogenic land-use and climate change are major threats to biodiversity, and consequently to ecosystem functions, although I could show that ecosystem functions such as herbivory and predation barely responded to temperature along a spatial gradient at present time. Yet, it is important to keep several points in mind: (i) The high rate of climate warming likely reduces the time that species will have to adapt to temperature in the future; (ii) Beyond mean temperatures, many aspects of climate will change; (iii) The compensation of biodiversity loss through functional redundancy in arthropod communities may be depleted at some point; (iv) Measures of ecosystem functions are limited by methodological filters, so that changes may be captured incompletely. Although much uncertainty of the effects of climate and land-use change on ecosystem functions remains, actions to halt biodiversity loss and to interfere with natural processes in an environmentally friendly way, e.g. reduction of herbivory on crops, are urgently needed. With this thesis, I contribute options to the environment-friendly regulation of herbivory, which are at least to some extent climate resilient, and at the same time make a contribution to halt biodiversity loss. Yet, more research and a transformation process is needed to make human action more sustainable. In terms of crop protection, this means that the most common method of treating pests with fast-acting pesticides is not necessarily the most sustainable. To realize sustainable strategies, collective efforts will be needed targeted at crop damage prevention through reducing pest populations and densities in the medium to long term. The sooner we transform human action from environmentally damaging to biodiversity promoting, the higher is our insurance asset that secures human well-being under a changing climate.