The principal aims of this work were to investigate dispersal activity of spiders
commonly found in agricultural crops, and to study the influence of both crop type and
farm operations on spider assemblages and populations. Work was also conducted to
develop and test an improved trapping method for samplmg aerially dispersing
(ballooning) spiders. Objectives were to determine whether common farmland species
exhibited species-specific differences in dispersal activity. Behavioural data from wind
chamber studies were also related to field data to establish i f seasonality in dispersal
was related to seasonal changes in dispersal motivation or variation in ground
population densities. Ground population data were used to determine if field-scale
differences in spider assemblage were related to crop type, and if crop-specific
management was associated with variable impacts on spider populations.
The improved trapping method ('stick and bottle' trap) was observed to increase catch
sizes significantly (F(i,i8) = 30.11, P < .0001) compared to climbing-sticks with trapping
adhesive. Total catch size over an eleven day period was 564 spiders. The use of an
'interception net' increased catch sizes threefold. Average loss of spiders from the traps
was 9.1% ± 7.7% for daylight hours between 09:00 and 17:00.
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The common Imyphiid spiders Engom atra, Oedothorax fuscus and Tenuiphantes
tenuis were observed to display different patterns of dispersal over time. Patterns were
similar for closely related species. Under wind chamber conditions, ballooning related
activity in E atra comprised almost one third of total activity time yet was vitually
absent in O. fuscus. Erigone atra was observed to balloon more frequently than O.
fuscus m the field - it is suggested that factors influencing the tendency to balloon are
different for these species. Ground populations related positively to balloonmg activity
for Oedothorax spp. females and dentipalpis males. For other species the high
efficiency of the trapping method may have reduced applicability to local ground
populations Seasonal differences in ballooning motivation observed in E atra females
in the wind chamber were likely related to differences in seasonal temperature affecting
activity and not ballooning motivation
Variation in spider assemblage composition was observed for fields under different
management and crop production. Correspondence analysis suggested vegetation
structure may mfluence the abundance of some species Set-aside was observed to have
a higher proportion of non-lmyphiid species than other fields Oedothorax fuscus was
dominant in almost all crops which could relate to its affinity for grass leys which
predommate m the landscape.
Harvesting m cereals and grass were seen to negatively impact spider populations with
declmes of 96% and 83% observed respectively withm nme days of harvestmg Post
harvest emigration was thought to contribute to these reductions Harvesting in maize
however had a neglible impact on spider populations with relative high densities of
adults overwmtering in maize stubble
Date of Award | 2009 |
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Original language | English |
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Awarding Institution | |
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ESTIMATING POPULATION CHANGE AND DISPERSAL ACTIVITY OF SPIDERS IN AN AGRICULTURAL LANDSCAPE
WOOLLEY, C. (Author). 2009
Student thesis: PhD