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Modelling life history/dispersal-strategy interactions to predict and manage linyphiid spider diversity in agricultural landscapes

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  • Self-employed clockmaker
  • Blackshaw Research & Consultancy
... Further development of the model presented here will include meteorological data of wind speeds and directions on different days in the year to estimate the twodimensional area over which linyphiid spiders can range. Further parameterization with species-specific data on other aspects of dispersal behaviour and population dynamics, together with landscape structure, will enable an evaluation of the different levels of risk individual species experience in agricultural landscapes (Thomas et al. 2003). Such a model will have important applications in the management of sustainable agriculture and the survival, persistence and diversity of this important guild of natural predators. ...
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Summary • Dispersal parameters are critical for modelling spatially dynamic populations yet remain among the most difficult to quantify. Linyphiid spider aerial dispersal by ‘ballooning’ on silk threads is dependent on meteorological factors and amenable to analysis and quantification. • Spider aerial activity was measured during consecutive 10-min periods for up to 11 h a day. Aerial density was measured at four heights using sticky traps. The time intervals between successive flights were measured by observing spiders landing and taking-off. • Meteorological measurements (wind speeds and temperatures) were taken simultaneously with the collection of airborne spiders, and used to calculate Richardson numbers to estimate atmospheric turbulence. • Numbers of airborne spiders on any given day, and their vertical density profile on different days, were significantly correlated with Richardson numbers. • Single flight distances were modelled using estimates of ascent and descent rates, the vertical density profile of airborne spiders and the wind speeds they experience aloft. The distributions of single flight distances and the time spent between successive flights were combined in an alternating renewal process to model the number of flights and the total daily dispersal distances of ballooning spiders as a function of available dispersal time. • On a day with, for example, 6 h of suitable weather, linyphiid spiders can potentially disperse a mean distance of approximately 30 km downwind. • Synthesis and applications. We have developed a dispersal model of linyphiid spiders that is central to the further development of spatially dynamic population models of these spiders in agricultural landscapes. It could also be adapted for application to other wind-borne organisms. Such models have a key role in the future management of sustainable agricultural systems where natural predators are seen as major components of pest control.
... Aerial dispersal by ballooning is a key strategy in the life histories of many spiders, especially pioneers of disturbed, patchy habitats exemplified by linyphiids in agricultural landscapes (Thomas et al. 2003a). Quantifying the dispersal power of these species is a necessary prerequisite for accurately modeling spatial population dynamics and developing successful sustainable management strategies. ...
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An unattended trap was designed to sample and retain spiders dispersing from agricultural grassland and crops. Traps comprised a removable bottle-trap fixed to the top of a vertical metal rod or “climbing-stick” that spiders climbed during normal pre-ballooning behavior. Bottle-traps caught over eight times more spiders than sticks treated with insect trapping adhesive. Draping sticks with nets increased the effective area of the traps and increased the catch size threefold. On average, 9.1% of spiders were lost from traps during the daytime sampling period. No difference in average rate of loss of spiders from the bottle-traps was observed between night and daylight hours. The bottle-trap design is economical and simple to construct, erect and operate. Continuous sampling also allows multiple traps to be used simultaneously in various locations.
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