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1 Egg laying on patchy resources and the importance of spatial scale. By Marc Hasenbank, Stephen Hartley School of Biological Sciences, VUW.

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Presentation on theme: "1 Egg laying on patchy resources and the importance of spatial scale. By Marc Hasenbank, Stephen Hartley School of Biological Sciences, VUW."— Presentation transcript:

1 1 Egg laying on patchy resources and the importance of spatial scale. By Marc Hasenbank, Stephen Hartley School of Biological Sciences, VUW

2 2 Overview Background Aim Hypothesis Experimental setup Results Summer06 Distribution of cabbage white eggs measured at different spatial scales Marc Hasenbank Ecology Conference 2006 - Wellington

3 3 Background – the basic Question Marc Hasenbank Ecology Conference 2006 - Wellington = Cabbage plant Cabbage white (Pieris rapae) How are the eggs distributed?

4 4 Resource concentration hypothesis : specialized herbivorous insects are more likely to find and stay in more dense and less diverse patches of their host plants (Root, 1973, Ecol. Monog. ). Background – Key Hypothesis Marc Hasenbank Ecology Conference 2006 - Wellington

5 5 Resource dilution hypothesis : insects are likely to locate diffused resource patches more often than expected (e.g. Yamamura, 2002, Pop. Ecol.). Background – Key Hypothesis Marc Hasenbank Ecology Conference 2006 - Wellington

6 6 Examples for resource concentration : - cinnabar moth, Tyria jacobaea, utilising ragwort (Harrison, 1995; Kunin, 1999) - chrysomelid beetle, Trirhabda virgata (Long, 2003) Examples for resource dillution : - seed-head fly, Botanophila seneciella, utilising ragwort (Crawley, 1988) - Pieris rapae butterflies ovipositing on Brassicaceae (Root, 1984) Background – Species dependent response Marc Hasenbank Ecology Conference 2006 - Wellington

7 7 Background Marc Hasenbank Ecology Conference 2006 - Wellington = Cabbage plant Cabbage white (Pieris rapae) How are the eggs distributed? But it is already documented, that cabbage white females tend to spread their eggs among plants in low density stands. But how is low and high density defined?

8 8 By changing the scale of observation, different areas of low or high resource density may be identified. Background Small scale Marc Hasenbank Ecology Conference 2006 - Wellington

9 9 By changing the scale of observation, different areas of low or high resource density may be identified. Background Medium scale Marc Hasenbank Ecology Conference 2006 - Wellington

10 10 By changing the scale of observation, different areas of low or high resource density may be identified. Background Coarse scale Marc Hasenbank Ecology Conference 2006 - Wellington

11 11 What at small scale seemed to be dense cluster might become an area of low resource density at coarse scale. Background High Low Medium Marc Hasenbank Ecology Conference 2006 - Wellington

12 12 We want to test whether it is possible to simultaneously observe resource concentration or resource dilution responses to patch density, simply by changing the scale of analysis. In particular… Do female cabbage white butterflies ( CW ), Pieris rapae, show scale- dependent responses to host plant density? Aim To answer these questions we measured the distribution of CW eggs among cabbage plants. Marc Hasenbank Ecology Conference 2006 - Wellington

13 13 Hypothesis – Plant densities H 0 Eggs are evenly distributed among different plant densities H A More eggs are found on plants in low density stands Marc Hasenbank Ecology Conference 2006 - Wellington

14 14 Hypothesis – Measurement at different spatial scales H 0 There is no difference between fine, medium and coarse scale measurements H A The observed response varies between different scales of measurement Marc Hasenbank Ecology Conference 2006 - Wellington

15 15 Experimental setup 100m 150m 36m P E F G H Number of Plants in Patches: P:180 E-H: 61

16 16 Experimental setup 100m 150m 36m 18m 14 4016 44 4 44 40 36m

17 17 Experimental setup 36m 18m 1 36m 18m 4 4016 44 4 44 40 4114 1 16 11 1111 1114 6m

18 18 Experimental setup Plant densities at different scales of measurement: 1x1m: 1416 6x6m: 141640 36x36m:61180

19 19 Results – Number of eggs/plant [mean+/-sem] vs plant densities at different scales for experiment Levin2 Marc Hasenbank Ecology Conference 2006 - Wellington

20 20 Results – Number of eggs/plant [mean+/-sem] vs plant densities at different scales for experiment Levin2 Marc Hasenbank Ecology Conference 2006 - Wellington

21 21 Conclusion Marc Hasenbank Ecology Conference 2006 - Wellington H 0 Eggs are evenly distributed among different plant densities H A More eggs are found on plants in low density stands

22 22 Conclusion Marc Hasenbank Ecology Conference 2006 - Wellington H 0 There is no difference between fine, medium and coarse scale measurements H A The observed response varies between different scales of measurement

23 23 Thanks to… Marc Hasenbank Ecology Conference 2006 - Wellington Stephen Hartley Jim Barrit Shirley Pledger Bug Group Special thanks to John Clark and the staff of Woodhaven Farm (Levin)


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