No abstract

Dispersal is an ecological phenomenon which is of fundamental importance to population biology. While dispersal behaviour of many orders of winged insects has received a great deal of attention, the dispersal characteristics of odonates have been poorly documented. We used capture-mark-recapture techniques to study dispersal behaviour of seven species of odonates breeding on a network of 11 small ponds in Cheshire, U.K. The ponds ranged in size from 615 to 1300 m(2) and varied from 30 to 860 m apart. We found surprisingly high rates of dispersal between ponds, with 10-47% per species of recaptured individuals moving from their natal pond. The mean probability of dispersal differed significantly among species but the relationship between the probability of dispersal and distance moved consistently followed a simple negative exponential curve for all species. Most individuals stayed at their natal pond, but a few moved long distances. Neither the age at which an individual was marked (teneral vs sexually mature) nor its sex significantly affected its tendency to disperse. The negative exponential relationship suggests that dispersal should be relatively easy to incorporate in more complex models of odonate spatio-temporal dynamics. To our knowledge, this is the first large-scale, multi-species study to assess dispersal behaviour of odonates by direct observation.Peer reviewe

No abstract

Crop rotations are allocations by growers of crop types to specific fields through time. This paper aims at presenting i) a systematic and rigorous mathematical representation of crops rotations; and ii) a concise mathematical framework to model crop rotations, which is useable on landscape scale modelling of agronomical practices. Rotations can be defined as temporal arrangements of crops and can be classified systematically according to their internal variability and cyclical pattern. Crop sequences in a rotation can be quantified as a transition matrix, with the Markovian property that the allocation in a given year depends on the crop allocated in the previous year. Such transition matrices can represent stochastic processes and thus facilitate modelling uncertainty in rotations, and forecasting of the long-term proportions of each crop in a rotation, such as changes in climate or economics. The matrices also permit modelling transitions between rotations due to external variables. Computer software was developed that incorporates these techniques and was used to simulate landscapescale agronomic processes over decadal periods.

In this study we assessed whether individuals of the damselfly species Ischnura elegans and Coenagrion puella that moved between ponds differed in their mean characteristics from individuals that did not move. Overall, the sex (female) and species (C. puella) that spent the most time away from the breeding site was more likely to move between ponds. Ischnura elegans males that dispersed had significantly longer forewings than males that did not, while male C. puella parasitised by water mites were more likely to disperse than unparasitised males. There was no evidence for differences in dispersal rates among the female colour forms of either I. elegans or C. puella. In general, the differences in dispersal characteristics between sexes and species could be explained by underlying variation in activity and mobility. The majority of dispersal between breeding sites by C. puella and I. elegans did not appear to be directed, but probably arose from chance movements occasionally taking individuals to a different pond from which they emerged.