Thomas F. Döring

What do we know about geographical knowledge spillovers and regional growth?: A survey of the literature

Döring T. and Schnellenbach J. (2006) What do we know about geographical knowledge spillovers and regional growth?: a survey of the literature, Regional Studies 40, 375–395. Modern (endogenous) growth theory tells us that knowledge is crucial for the sustained growth of high-income economies. Against this background, the paper provides a survey of theoretical and empirical findings highlighting the question of how geographically limited knowledge diffusion can help to explain clusters of regions with persistently different levels of growth. It discusses this topic in two steps. First, the theoretical concept of knowledge spillovers is outlined by discussing the different types of knowledge, the spatial dimension of knowledge spillovers, and the geographical mechanisms and structural conditions of knowledge diffusion. Second, it analyses the empirical evidence concerning the theoretical propositions. Döring T. and Schnellenbach J. (2006) What do we know about geographical knowledge spillovers and regional growth?: a survey of the literature, Regional Studies 40, 375–395. Modern (endogenous) growth theory tells us that knowledge is crucial for the sustained growth of high-income economies. Against this background, the paper provides a survey of theoretical and empirical findings highlighting the question of how geographically limited knowledge diffusion can help to explain clusters of regions with persistently different levels of growth. It discusses this topic in two steps. First, the theoretical concept of knowledge spillovers is outlined by discussing the different types of knowledge, the spatial dimension of knowledge spillovers, and the geographical mechanisms and structural conditions of knowledge diffusion. Second, it analyses the empirical evidence concerning the theoretical propositions. Retombées de connaissance, Croissance régionale, Recherche et développement, Innovation, Diffusion des innovations Döring T. and Schnellenbach J. (2006) What do we know about geographical knowledge spillovers and regional growth?: a survey of the literature, Regional Studies 40, 375–395. Modern (endogenous) growth theory tells us that knowledge is crucial for the sustained growth of high-income economies. Against this background, the paper provides a survey of theoretical and empirical findings highlighting the question of how geographically limited knowledge diffusion can help to explain clusters of regions with persistently different levels of growth. It discusses this topic in two steps. First, the theoretical concept of knowledge spillovers is outlined by discussing the different types of knowledge, the spatial dimension of knowledge spillovers, and the geographical mechanisms and structural conditions of knowledge diffusion. Second, it analyses the empirical evidence concerning the theoretical propositions. Nebenwirkung von Kenntnissen, regionales Wachstum, Forschung und Entwicklung, Innovation, Verbreitung von Innovationen Döring T. and Schnellenbach J. (2006) What do we know about geographical knowledge spillovers and regional growth?: a survey of the literature, Regional Studies 40, 375–395. Modern (endogenous) growth theory tells us that knowledge is crucial for the sustained growth of high-income economies. Against this background, the paper provides a survey of theoretical and empirical findings highlighting the question of how geographically limited knowledge diffusion can help to explain clusters of regions with persistently different levels of growth. It discusses this topic in two steps. First, the theoretical concept of knowledge spillovers is outlined by discussing the different types of knowledge, the spatial dimension of knowledge spillovers, and the geographical mechanisms and structural conditions of knowledge diffusion. Second, it analyses the empirical evidence concerning the theoretical propositions. Desbordamientos de conocimiento, Crecimiento regional, Investigación y desarrollo, Innovación, Divulgación de innovaciones

Unravelling the evolution of autumn colours: an interdisciplinary approach

Leaf colour change is commonly observed in temperate deciduous forests in autumn. This is not simply a side effect of leaf senescence, and, in the past decade, several hypotheses have emerged to explain the evolution of autumn colours. Yet a lack of crosstalk between plant physiologists and evolutionary ecologists has resulted in slow progress, and so the adaptive value of this colour change remains a mystery. Here we provide an interdisciplinary summary of the current body of knowledge on autumn colours, and discuss unresolved issues and future avenues of research that might help reveal the evolutionary meaning of this spectacle of nature.

Visual ecology of aphids—a critical review on the role of colours in host finding

We review the rich literature on behavioural responses of aphids (Hemiptera: Aphididae) to stimuli of different colours. Only in one species there are adequate physiological data on spectral sensitivity to explain behaviour crisply in mechanistic terms. Because of the great interest in aphid responses to coloured targets from an evolutionary, ecological and applied perspective, there is a substantial need to expand these studies to more species of aphids, and to quantify spectral properties of stimuli rigorously. We show that aphid responses to colours, at least for some species, are likely based on a specific colour opponency mechanism, with positive input from the green domain of the spectrum and negative input from the blue and/or UV region. We further demonstrate that the usual yellow preference of aphids encountered in field experiments is not a true colour preference but involves additional brightness effects. We discuss the implications for agriculture and sensory ecology, with special respect to the recent debate on autumn leaf colouration. We illustrate that recent evolutionary theories concerning aphid–tree interactions imply far-reaching assumptions on aphid responses to colours that are not likely to hold. Finally we also discuss the implications for developing and optimising strategies of aphid control and monitoring.

Impacts of climate change on plant diseases—opinions and trends

There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases. This overview addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods.

Seed exchange networks for agrobiodiversity conservation. A review.

The circulation of seed among farmers is central to agrobiodiversity conservation and dynamics. Agrobiodiversity, the diversity of agricultural systems from genes to varieties and crop species, from farming methods to landscape composition, is part of humanity’s cultural heritage. Whereas agrobiodiversity conservation has received much attention from researchers and policy makers over the last decades, the methods available to study the role of seed exchange networks in preserving crop biodiversity have only recently begun to be considered. In this overview, we present key concepts, methods, and challenges to better understand seed exchange networks so as to improve the chances that traditional crop varieties (landraces) will be preserved and used sustainably around the world. The available literature suggests that there is insufficient knowledge about the social, cultural, and methodological dimensions of environmental change, including how seed exchange networks will cope with changes in climates, socio-economic factors, and family structures that have supported seed exchange systems to date. Methods available to study the role of seed exchange networks in the preservation and adaptation of crop specific and genetic diversity range from meta-analysis to modelling, from participatory approaches to the development of bio-indicators, from genetic to biogeographical studies, from anthropological and ethnographic research to the use of network theory. We advocate a diversity of approaches, so as to foster the creation of robust and policy-relevant knowledge. Open challenges in the study of the role of seed exchange networks in biodiversity conservation include the development of methods to (i) enhance farmers’ participation to decision-making in agro-ecosystems, (ii) integrate ex situ and in situ approaches, (iii) achieve interdisciplinary research collaboration between social and natural scientists, and (iv) use network analysis as a conceptual framework to bridge boundaries among researchers, farmers and policy makers, as well as other stakeholders.

Which carabid species benefit from organic agriculture? - a review of comparative studies in winter cereals from Germany and Switzerland

Data of comparative studies about carabid beetles in organically and conventionally managed winter cereal fields of central Europe, using the pitfall trapping method, were collected from the literature and unpublished data sources and were then pooled and analysed. According to an index, which was designed to calculate how much a species benefits from organic management, Carabus auratus turned out to benefit most. Some Amara species (A. familiaris, A. similata and A. aenea) as well as Pseudoophonus rufipes and Harpalus affinis also showed high index values. When analysing the traits of the carabids, the habitat preference was the most important variable for the differentiation of organic and conventional management. The stronger the preference for open field, the more the species are supported by organic agriculture. For the promotion of the agricultural carabid fauna it is suggested that weedier and less densely cropped fields be tolerated.

Autumn leaves seen through herbivore eyes

Why leaves of some trees turn red in autumn has puzzled biologists for decades, as just before leaf fall the pigments causing red coloration are newly synthesized. One idea to explain this apparently untimely investment is that red colour signals the trees quality to herbivorous insects, particularly aphids. However, it is unclear whether red leaves are indeed less attractive to aphids than green leaves. Because aphids lack a red photoreceptor, it was conjectured that red leaves could even be indiscernable from green ones for these insects. Here we show, however, that the colour of autumnal tree leaves that appear red to humans are on average much less attractive to aphids than green leaves, whereas yellow leaves are much more attractive. We conclude that, while active avoidance of red leaves by aphids is unlikely, red coloration in autumn could still be a signal of the trees quality, or alternatively serve to mask the over-attractive yellow that is unveiled when the green chlorophyll is recovered from senescing leaves. Our study shows that in sensory ecology, receiver physiology alone is not sufficient to reveal the whole picture. Instead, the combined analysis of behaviour and a large set of natural stimuli unexpectedly shows that animals lacking a red photoreceptor may be able to differentiate between red and green leaves.

Response of alate aphids to green targets on coloured backgrounds

To study the effect of background colour on aphid landing on green targets (water pan traps), two field experiments were set up in Hessen, Germany, in 2003. Traps were put onto coloured plastic sheets (13 colours, straw mulch, transparent foil, and uncovered soil, Experiment 1). In Experiment 2, green water pans were again put on coloured plastic sheets (red, white, green, and yellow), and the sheets were either sprayed with insect glue or not. Backgrounds and traps were spectrally characterised with a field radiometer (320–950 nm). Aphid catches were highest in the traps on the uncovered background, and lowest in the traps on white or silver backgrounds. For Brevicoryne brassicae, Myzus persicae (Homoptera: Aphididae, Macrosiphini) and five further aphid species, there was a significant negative correlation between UV‐reflectance (320–400 nm) and log(N + 1)‐transformed number of individuals. However, the effect of straw mulch (reduced aphid catches with straw compared to the uncovered background), could not be attributed to differences in UV‐reflectance, as UV was almost identical in soil and straw. High numbers of alate aphids were caught in traps with dark backgrounds (e.g. black, dark green), a result which was attributed to the high contrast between the background and target. The substantially higher aphid numbers from targets with bare soil than from targets with spectrally similar black backgrounds were thought to be caused by the structure of the background surface: for alate aphids, landing close to the target on smooth surfaces may induce probing, and the lack of appropriate substrate will result in take‐off, whereas soil will not induce probing, and aphids will continue to move towards the green targets.

Are autumn foliage colors red signals to aphids

Why do plants change color in the autumn? Could it be a signal to aphids, warning them of the defensive strength of the trees, or might the cause be more mundane?

Biotic indicators of carabid species richness on organically and conventionally managed arable fields

Abstract Carabids, a species rich arthropod family, potentially contribute much to biodiversity in agroecosystems, but assessing and monitoring carabid diversity is costly and time consuming. Therefore, this study aimed at finding more easily measurable parameters indicating high carabid diversity within organic and conventional management systems. Cover and number of weed species as well as activity density of single carabid species and of total carabids were investigated as potential indicators of carabid species richness. The study was carried out near Reckenfeld in Westphalia on sandy Plaggenesch soils. Three organically and four conventionally managed fields (cereals and corn) were investigated at the field margins and in the field centres from April to August 1999. Additionally, data of carabid catches and weed flora in winter cereals from an extended study in Duren (Northrhine-Westphalia) were reanalysed to validate the results. However, neither of the potential indicators showed consistently significant positive correlation with carabid diversity. This is partly attributed to the low variability of management conditions within the management systems in the studies presented.