Steps towards food web management on farms

F.W. Smeding

Research output: Thesisinternal PhD, WU

Abstract

<p>This paper is the report of four years of research on the functional group composition of the animal community in relation to farm and ecological infrastructure (E.I.) management on organic arable farms. The results are mainly based on abundance data of ground dwelling arthropods obtained by pitfall trapping, density data of vegetation dwelling arthropods by vacuum sampling and density data of insectivorous birds by territory mapping. Arthropods were collected in wheat crops (representing the crop area) and on the adjacent canal bank (representing the E.I.); the bird, farm and E.I. variables were measured at the farm level. Study areas included in total 18 farms with varying extents of organic duration, crop rotation intensity, and quantity and quality of E.I.</p><p>The hypothesis of the research was that the food web structure of an organic arable farm with long organic duration as well as with an improved E.I. ( <em>i.e.</em> enlarged, late mown), would show a higher abundance of meso- and macrofauna of both herbivorous and detritivorous functional groups. These enhanced primary groups were expected to carry a high predator abundance at both secondary ( <em>i.e.</em> invertebrates) as well as tertiary ( <em>i.e.</em> birds) levels. With regard to the crop areas it was found, in contradiction to the hypothesis, that herbivores were most abundant in crop areas of recently converted farms and of organic farms with intensive crop rotation; this herbivore abundance was associated with invertebrate predator abundance and species diversity. In accordance with the hypothesis, some evidence was found for increased detritivore and related epigeic predator abundance related to extensive crop management on the farms of long organic duration. Whilst studying the E.I., an increased abundance of vegetation dwelling predators and also detritivores was found in improved E.I. However K-herbivore numbers did not increase in the improved E.I. when they were compared to the traditionally managed E.I. The summer abundance of epigeic predators was also not related to an improved E.I. Field studies provided some evidence for the dispersal of functional groups, abundant in the E.I., towards the crop area. However, the effects of crop conditions on the arthropod abundance in the crop area were observed to offset the influence of the E.I. Bird studies at the farm level revealed positive correlation between bird functional groups and a combination of crop area and E.I. characteristics. Bird density was found to be positively associated with high arthropod abundance in the E.I. vegetation canopy. Observations also suggested positive correlation to an increased herbivory in the crop area of the long duration organic farms that had an intensive crop rotation.</p><p>A proposal for a descriptive or topological farm food web is drawn from field observations as well as from references in literature. Predictions are made for four different farm food web structures that express four extremes of two environmental gradients, which correspond to the length of organic duration and the amount/quality of the E.I. With reference to field observations important themes in the food web theory are discussed, including the indirect effects of subsidised detrital food chains on herbivore abundance and consequently on bird abundance, as well as the possible effects of intra guild predation on arthropod functional group composition.</p><p>The implications of the study are that organic duration and the amount/quality of the E.I. may contribute to improving ecosystem services and to aims based on nature conservation. However an optimisation of the farm food web with regard to ecosystem services may not necessarily improve nature conservation values. It is argued that increased understanding of the farm food web and its management is likely to support the development of multi-species agroecosystems that integrate improved ecosystem services and nature conservation goals.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Goewie, E.A., Promotor
  • van Bruggen, A.H.C., Promotor
  • Joenje, W., Promotor, External person
Award date6 Jun 2001
Place of PublicationS.l.
Print ISBNs9789058084149
Publication statusPublished - 2001

Keywords

  • ecology
  • landscape ecology
  • farms
  • farming systems
  • biodiversity
  • predator prey relationships
  • organic farming
  • ecological balance
  • plant ecological groups
  • pest management
  • agroecology

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