Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. SPIDER DISTRIBUTION IN AGROECOSYSTEMS IN CANTERBURY, NEW ZEALAND A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University by A.R. G. McLachlan Lincoln University 2000 This thesis is dedicated to the memory of Ellen Annie Tricker 20.i.1922 - 22.ix.1996 Nana ... naturalist ... hardcase and Josephus Joannes Schepers 17.ii.1931 - 21.i.2000 friend page 11 I am glad I did it, partly because it was well worth it, and chiefly because I shall never have to do it again. Mark Twain Intriguing paradoxes define the spider persona as presently understood. The spider is food limited, yet does not compete for prey. Thus spiders do not consume enough prey to lower the prey availability substantially for other spiders. This suggests that spiders do not limit population densities of their prey. Furthermore, the foraging behavior of spiders and their life history characteristics lead to the prediction that spiders should not regulate prey populations, i.e. should not inflict pronounced density­ dependent mortality on their prey. Thus individual species of spiders should not be good biocontrol agents in agroecosystems. Indirect evidence, based on estimates of energy flow through the entire community, and direct evidence from field experiments contradict these expectations. However, experimental studies are too few in number to support firm generalizations about the role of spiders in limiting insect numbers. Results so far lead to an enigmatic portrait of the spider persona; its role is clear in some scenes, but only dimly perceived in other acts. Many scripts it follows are still obscure. David Wise, 1993. Spiders in ecological webs. Cambridge University Press. p. 262. page iii Abstract The spider assemblage from four shelterbelts and their adjacent grazed pastures in South Island, New Zealand was suction sampled from August 1994 to July 1995 and from March 1996 to March 1997. Spider density decreased rapidly with distance from the field margin (mean 2411m2) to 72.5/m2 at 2.5 m and 10.3/m2 at 5 m into the pasture. Fenced shelterbelts had 6.7 times more spiders and 3-10 more species than did the adjacent pasture. The most common pasture species was the European linyphiid Lepthyphantes tenuis (Blackwall) (37% of individuals) but, in shelterbelts, L. tenuis was equally common at 26% with an unidentified endemic theridiid species at 25%. Eleven shelterbelts were suction sampled in November 1995 and had spider 2 2 densities ranging from 621m to 369/m , and species richness ranging from 6 to 12 from a 1 m2 sample area at each site. Twenty-three species were recorded; three were introduced European linyphiids, the rest were native or endemic to New Zealand. Spider density was compared in three pasture types (cocksfoot and clovers, lucerne, and rye grass and clovers) both in open and agroforestry pasture (between rows of Pinus radiata trees). There were no differences between either open and agroforestry pasture, or the three pasture types. Spider density was not correlated with vegetation height or cover, although L. tenuis density was positively correlated with vegetation height characteristics in open pasture. Mowing ungrazed pasture plots reduced both spider density and species richness. Unmown plots had a fauna and density similar to those of shelterbelts, but mown plots had a density similar to those in grazed pasture. Field cage experiments in a lucerne (Medicago sativa L.) crop and in broad bean (Vicia/aba L.) plots to investigate the effects of spider density on pea aphid (Acyrthosiphon pisum (Harris)) abundance, showed that a large number of replicates (46 or more) were needed to detect differences in aphid abundance between spider density treatments. Aphid densities reached unnaturally high levels due to the sheltered cage conditions. The results are discussed in the context of the effects of pastoral agricultural practices in New Zealand on spider density, distribution, species composition, and potential in pest management. page iv Contents Abstract.................................................................................................................. iv Contents.................................................................................................................. v List of Tables .....................................................................................................viii List of Fig u res ...................................................................................................... x Chapter 1 : General introduction .............................................................. 1 Research objectives of this thesis ..................................................................... 6 Chapter 2 : Sampling methods .................................................................. 7 Introduction ........................................................................................................... 7 Methods .................................................................................................................. 7 Standard Vortis sample ................................................•..........•......................... 7 Efficiency test 1 .................................................................................................. 8 Efficiency test 2 ..................................................................................•............... 9 Effect of sample duration ......................................•.................•....................... 10 Results .................................................................................................................. 10 Efficiency Test 1 ............................................................................................... 10 Efficiency Test 2 ............................................................................................... 11 Effect of duration ............................................................................................. 12 Discussion ........................................................................................................... 13 Test 1 ................................................................................................................. 13 Test 2 ................................................................................................................. 14 Effect of duration ............................................................................................. 15 Conclusions ...................................................................................................... 16 Chapter 3 : Field-margin and pasture spider communities in Canterbury, New Zealand ................................................................ 17 Abstract ................................................................................................................ 17 Introduction ..................................................................•...................................... 17 Methods .........................................................•...................................................... 19 Spider densities in relation to distance from field margin .................•......... 19 Spider densities in four pastures and shelterbelts ........................................ 19 Site descriptions ............•.•................ ~ .......................•....•................•.............•... 19 Sampling procedures .......•............................................•.................................. 20 Results .................................................................................................................• 21 Spider densities in relation to distance from field margin ........................... 21 Spider densities in four pastures and shelterbelts ........................................ 23 Discussion ........................................................................................................... 27 Acknowledgments ............................................................................................. 29 Chapter 4 : Spider fauna and abundance in fenced-off shelterbelts ............................................................................................. 30 Introduction .................................................................•..............................•........ 30 Methods ................................................................................................................ 30 Site descriptions ............................................................................................... 30 Results .................................................................................................................. 32 Discussion ........................................................................................................... 32 Contents Chapter 5 : Spider faunal composition and densities in pasture in the Lincoln University Agroforestry Experiment