Transcript sfloresmejia 2014 ESAx

Temperature responses of a plant-herbivore-parasitoid system using a
‘Tri-trophic food-web performance ratio’ approach
Sandra
1Département
1
Flores-Mejia ,
Valérie
de Biologie, Université Laval
2
Fournier ,
Conrad
2Département
1.
Cloutier
de Phytologie, Université Laval
•
INTRODUCTION
Each component of a multi-trophic food web has its own thermal window1. Climate change is
believed to have a higher impact in higher trophic levels of the food web, because they depend
on the capacity of adaptation of the lower levels and because they have a smaller thermal
window2, 3.
One limitation when studying a food web is lack of a measure of performance that can be
used to directly compare its components, including the host plant, which has a different biology
than insect herbivores and carnivores. The product of rm * biomass has been suggested as a
parameter to evaluate the performance of herbivores with respect of a plant4,5,6. Here we
propose the “Tri-trophic food-web performance ratio” (φ), as a common measure to evaluate a
plant base food web as affected by temperature.
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OBJECTIVES
Determine the temperature profile of a tri-trophic food web and determine which trophic level
is more likely to outperform the others under a wide range of different thermal conditions.
RESULTS
Biomass accumulation can be a useful to evaluate the performance of a food web, both for
individual components and as a whole. Each level of our experimental food web has a different
temperature profile, and thus they maximize biomass accumulation rate at different
temperatures (Figure 1):
• Plants (Figure 1A): have the widest temperature range, going above 28°C. In spite of the
different temperature preferences between peppers and potatoes, both perform better at midtemperatures
• Herbivore (Figure 1B): perform better at lower temperatures, with no growth above 28°C.
Aphid productivity will depend on the host plant it is exploiting.
• Parasitoid (Figure 1C): has the smallest temperature range, having very low performance at
both low and high temperatures. It is capable to similarly exploit aphids raised on different
host plants, showing its generalistic nature. Only sex ratio is significant for the parasitoid’s
biomass accumulation. As females are bigger than males (data not shown), a 40♂:60♀ sex
ratio will have a higher overall biomass than a 60♂:40♀.
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Develop a single parameter that can be used to evaluate the performance of a tri-trophic food
web under different temperature conditions.
MATERIALS AND METHODS
The food web model tested was formed by: three different host plants, one cultivar of potato
(S. tuberosum cv. “Norland”), and two cultivars of bell pepper (C. annuum cv. “Fascinato”© and
“Crosby”©). The herbivore was the potato aphid (Macrosiphum euphorbiae Thomas), biotype
POT; and finally the parasitoid wasp Aphidius ervi Halliday.
The experimental temperatures were: 8, 12, 16, 20, 24, 28, 32, and 36°C, with 65% R.H. and
16D:8N photoperiod. We obtained the mean relative growth rate (mRGR)7of the three plants,
when infested with 0, 10, 40 L1 aphids per plant type and per temperature. We obtained the net
reproduction rate (Ro)8 and the adult biomass of both aphids and parasitoids, for each
combination of host plant-aphid biotype per temperature. We then calculated a Net Generational
Productivity (NGP)9 parameter for aphids and parasitoids, as the product of Ro*average adult
biomass. The “Tri-trophic food-web performance ratio” (φ3) parameter was finally calculated
using the formula:
NGPh - NGPp
φ3' 
mRGR * L
Where NGPh NGPp stand for the net generational productivity of the herbivore (aphid) and
carnivore (parasitoid) , respectively. The mRGR is the average relative growth rate of the plant,
and L is a fixed time, chosen to be the average aphid lifetime (in days) for which the NGPh was
calculated.
Click here to enlarge figure
Figure 1: Individual models for each of the components of the “Tri-trophic food web ratio”: A) mRGR of the
three host plants; B) NGP of the herbivore, the potato aphid, (M. euphorbiae) and C) NGP of the parasitoid, the
wasp A. ervi. All three components were tested at eight constant temperatures between 8 and 36°C.
Click here to enlarge figure
Figure 2: Tri-trophic food web ratio at six constant temperatures
Temperature response of the tri trophic food web ratio, summarized in Figure 2, showed that:
• At low temperatures (below 15˚C), the herbivores outperform both plants and parasitoids
(positive values of φ3).
• At mid-temperatures, the parasitoids have the advantage above the other two components
(negative values), especially when the sex ratio is more female oriented.
• At high temperature (30˚C or above), it is the plant that has a slight competitive advantage
over both herbivores and parasitoids (φ3 values between -1 and 1).
This is the first attempt to evaluate a food web performance with a single parameter allowing
direct quantitative comparison of different levels. This parameter can be used to evaluate the
food web under different scenarios, such as those of climate change.
REFERENCES
1. Dixon, A.F.G., Honěk, A., Keil, P., Kotela, M.A.A., Šizling, A.L., & Jarošík, V. (2009) Relationship between the minimum and maximum temperature
thresholds for development in insects. Functional Ecology, 23, 257-264.
2. Jeffs, C.T. & Lewis, O.T. (2013) Effects of climate warming on host–parasitoid interactions. Ecological Entomology, 38, 209-218.
3. Van Baaren, J., Le Lann, C., & van Alphen, J. (2010). Consequences of climate change for aphid-based multi-trophic systems. In Aphid Biodiversity
Under Environmental Change. Patterns and Processes (ed. by P. Kindlmann, A.F.G. Dixon & J.P. Michaud), pp. 55-68. Springer Science & Business
Media.
4. Fenchel, T. (1974) Intrinsic rate of natural increase: The relationship with body size. Oecologia, 14, 317-326.
5. Lamb, R.J., MacKay, P.A., & Migui, S.M. (2009) Measuring the performance of aphids: fecundity versus biomass. The Canadian Entomologist, 141, 401405.
6.Van Impe, G. & Hance, T. (1991) Étude comparative de la biomasse des populations d'Aphis fabae SCOPOLI (Homoptera: Aphididae) et de Tetranychus
urticae KOCH (Acari:Tetranychidae). In 43rd International Symosium of Crop Protection, Vol. 56, pp. 343-354. Mededelingen van de Faculteit
Landbouwwetenschappe, Gent.
7.Penaloza P, Palma B & Silva C (1996) Plant growth and reproductive development of Capsicum annuum L. Phyton-International Journal of Experimental
Botany 59: 187-195.
8. Birch LC (1948) The intrinsic rate of natural increase of an insect population. Journal of Animal Ecology 17: 15-26.
9. Flores-Mejia, S., Fournier, V., & Cloutier, C. 2014 Temperature responses of a plant-insect system using a food-web performance approach.
Entomologia Experimentalis et Applicata.
ACKNOWLEDGMENTS
We thank RZH Canada Ltd and Syngenta seeds for graciously providing us with the bell pepper seeds. We also thank J.F.Guay, A. Auger, Y. Gobeil, E.
Morin and E. Lemaire for their assistance in experimental work, Funding for this project was provided by: NSERC-Strategic and Discovery Grants, Centre
SÈVE, and Ministère de l’Éducation, du Loisir et du Sport du Québec.
Figure 1: Individual models for each of the components of the “Tri-trophic food web ratio”: A) mRGR of the three host plants; B)
NGP of the herbivore, the potato aphid, (M. euphorbiae) and C) NGP of the parasitoid, the wasp A. ervi. All three components
were tested at eight constant temperatures between 8 and 36°C.
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Figure 2: Tri-trophic food web ratio at six constant temperatures
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