Stockdale, E. A., Lampkin, N. H., Hovi, M., Keatinge, R., Lennartsson, E. K. M., Macdonald, D. W., Padel, S., Tattersall, F. H., Wolfe, M. S., Watson, C. A. (2001). Agronomic and environmental implications of organic farming systems. Advances in Agronomy, 70, 261-327.

Agronomic and environmental implications of organic farming systems.

Relative importance of vertebrates and invertebrates in epigeaic weed seed predation in organic cereal fields

Summary
1Monitoring of exposure to pesticides in many countries shows extensive exposure of predators to anticoagulant rodenticides, which are used to control rats. Many predators and scavengers are declining in numbers, and exposure to rodenticides might therefore be of importance in conservation biology.
2Predators and scavengers of poisoned rats are at most risk of secondary poisoning. However, several predatory species of conservation concern rarely eat rats, implicating non-target small mammals as the major route of exposure. For the first time, this research investigated the importance of non-target small mammals as routes of exposure to rodenticide for predators and scavengers in the UK.
3Exposure studies of non-target small mammals were carried out alongside routine rat control at five sites, around agricultural buildings (n = 2) and feed hoppers for game birds (n = 3).
4Three non-target rodent species fed on rodenticide from bait boxes during routine rat control treatments. A large proportion (48·6%) of individuals in local populations ate the bait: woodmice Apodemus sylvaticus were most exposed, followed by bank voles Clethrionomys glareolus then field voles Microtus agrestis.
5Local populations of non-target small mammals declined significantly following rodenticidal rat control but their relative proportions did not change significantly. Populations recovered partially after 3 months, depending on the time of the year relative to the breeding cycle.
6Synthesis and applications. Our results clearly demonstrate that routine rat control reduced local populations of non-target small mammals. This may limit the food supply of some specialist predators. Most importantly, this demonstrates a significant route of exposure of predators and scavengers of small mammals to secondary poisoning. Rodenticides are applied on farms and game estates across the UK. Hence the results of this study are indicative of non-target rodenticide exposure nationally. Mitigation requires a shift from the current reliance on rodenticides to ecologically based rodent management, involving improvements in site management and the adoption of good farming practice.

Exposure of non‐target small mammals to rodenticides: short‐term effects, recovery and implications for secondary poisoning

We investigated the role of host sex in parasite transmission and questioned: ‘Is host sex important in influencing the dynamics of infection in free living animal populations?’ We experimentally reduced the helminth community of either males or females in a yellownecked mice (Apodemus flavicollis) population using an anthelmintic, in replicated trapping areas, and subsequently monitored the prevalence and intensity of macroparasites in the untreated sex. We focussed on the dominant parasite Heligmosomoides polygyrus and found that reducing parasites in males caused a consistent reduction of parasitic intensity in females, estimated through faecal egg counts, but the removal of parasites in females had no significant influence on the parasites in males. This finding suggests that males are responsible for driving the parasite infection in the host population and females may play a relatively trivial role. The possible mechanisms promoting such patterns are discussed.

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The role of host sex in parasite dynamics: field experiments on the yellow‐necked mouse Apodemus flavicollis

In this paper we summarize for the first time the effects of agriculture expansion and intensification on animal diversity in the Pampas of Argentina and discuss research needs for biodiversity conservation in the area. The Pampas experienced little human intervention until the last decades of the 19th century. Agriculture expanded quickly during the 20th century, transforming grasslands into cropland and pasture lands and converting the landscape into a mosaic of natural fragments, agricultural fields, and linear habitats. In the 1980s, agriculture intensification and replacement of cattle grazing-cropping systems by continuous cropping promoted a renewed homogenisation of the most productive areas. Birds and carnivores were more strongly affected than rodents and insects, but responses varied within groups: (a) the geographic ranges and/or abundances of many native species were reduced, including those of carnivores, herbivores, and specialist species (grassland-adapted birds and rodents, and probably specialized pollinators), sometimes leading to regional extinction (birds and large carnivores), (b) other native species were unaffected (birds) or benefited (bird, rodent and possibly generalist pollinator and crop-associated insect species), (c) novel species were introduced, thus increasing species richness of most groups (26% of non-rodent mammals, 11.1% of rodents, 6.2% of birds, 0.8% of pollinators). Much taxonomic and ecological work is still needed to understand Pampean animal biodiversity, to understand how agriculturization is affecting it, and to identify appropriate conservation actions. Networks of Important Bird Areas and Valuable Grassland Areas harbor a balanced representation of Pampean biodiversity and, if adequately protected, may provide valuable research sites, but complementary work should be carried out on agriculturized areas.

Effects of agriculture expansion and intensification on the vertebrate and invertebrate diversity in the Pampas of Argentina

Forty-eight wood mice Apodemus sylvaticus were radio-tracked over an estimated 1500 h yielding 9000 fixes. The mice were living in three contiguous arable fields, and showed that they respond to weedy microhabitat patches within superficially homogeneous crops. Plant species' abundance and the composition of the seed bank were assessed in quadrats taken in areas in which (a) mice foraged, (b) through which mice travelled, or (c) at random within each home range. Wood mice avoided foraging in areas with a high abundance of bare earth, and selected areas with a high abundance of Alopecurus myosuroides, Stellaria media, Avena fatua, Galium aparine or Bromus sterilis. The food plants apparently selected by wood mice differed markedly between months and between sexes. This may relate to the energetic and nutritional demands incurred by the contrasting reproductive tactics of male and female wood mice. There were no differences between seed bank samples taken from quadrats where the mice foraged, travelled through, or which were selected at random. Our study, the first large-scale analysis of wood mouse microhabitat preference using radio-tracking, reveals that whereas the mice do not react to heterogeneity on the scale of the mosaic of crop fields, they are greatly influenced by the dispersion of food plants within the superficially homogeneous crop itself.

Arable habitat use by wood mice (Apodemus sylvaticus). 2. Microhabitat

We investigated the effects of crop type on numbers and movements of wood mice Apodemus sylvaticus in field edges and in arable fields containing either winter wheat, winter barley or oil-seed rape, grown on a 3-year rotation. We also investigated the effect of habitat (field centre vs edge), and of season and year. This was done at the individual level using radio-tracking, and at the population level using live-trapping. Wood mouse population size (estimated as minimum number alive) was significantly affected by season. Wood mouse numbers also differed between crop types. Rape field centres and edges had significantly lower numbers than did barley or wheat field centres and edges. Populations were largest from April to July, when the crop was tall. In winter, significantly more mice were found in field edges compared with field centres. The patterns of movement of individual mice also showed differences between habitats and between seasons. Mice were found to move more quickly when they were tracked through rape compared with the other crops. When the crop was growing, they moved faster through field edges bordered with hedgerow than they did through wood. This pattern was reversed later in the year when the crop was tall. The distances moved during a session of tracking showed differences which paralleled those for speed of movement. Also, males tended to move faster than females. Differences between the sexes in movement patterns were affected by season; when the crop was down (in winter) females moved further than males during a session of tracking, but when the crop was growing and tall, this was reversed.

Arable habitat use by wood mice (Apodemus sylvaticus). 3. A farm-scale experiment on the effects of crop rotation

Rat movements and control on an Oxfordshire farm

The effects of trap spacing on population estimation of small mammals

We investigated the responses of the wood mouse ( Apodemus sylvaticus ) and bank vole ( Clethrionomys glareolus ) to odor in traps by examining the capture rate of live-traps with respect to their immediate trapping, and therefore semiochemical, history. Both bank voles and wood mice preferred traps previously occupied by conspecifics. However, bank voles showed no sexual bias to this preference, whereas wood mice exhibited a significant preference for traps that had been occupied by members of the opposite sex. In accordance with current theories on their breeding system, wood mice showed sexual differences, both in their reaction to the odor of members of the same sex and in the temporal nature of their reaction to conspecific odor. Wood mice also avoided traps that had previously held bank voles. The results indicate that live-trapping data may reveal important semiochemical interactions between both heterospecific and conspecific animals and highlight the need for caution, both in the deployment of traps and the analysis of data, when using such techniques for the enumeration of populations.

T. E. Tew

Papers

Arable habitat use by wood mice (Apodemus sylvaticus). 2. Microhabitat

Arable habitat use by wood mice (Apodemus sylvaticus). 3. A farm-scale experiment on the effects of crop rotation

Rat movements and control on an Oxfordshire farm

The effects of trap spacing on population estimation of small mammals

Temporal changes in olfactory preference in murid rodents revealed by live-trapping