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Disentangling associational effects: both resource density and resource frequency affect search behaviour in complex environments
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Number of Authors: 4
2016 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, no 11, 1826-1833 p.Article in journal (Refereed) Published
Abstract [en]

Neighbouring resources have been found to either decrease or increase the likelihood that a consumer organism attacks a focal resource. These phenomena are referred to as associational resistance (AR) and associational susceptibility (AS), respectively. While associational effects have been observed in various field studies, little is known on how resource heterogeneity can cause associational effects. We used a laboratory approach in which we studied the effects of resource density and frequency in the search behaviour of Drosophila melanogaster as a model organism for olfactory-guided behaviour in insects. We first determined whether D.melanogaster could discriminate between odour sources that differ quantitatively. Secondly, we determined what the effect of resource density and frequency was on the search behaviour of D.melanogaster by combining these resources into various patch arrangements. Finally, we used the outcome of our experiments to disentangle the role of resource density and frequency in associational effects. We found that D.melanogaster has the ability to discriminate between quantitatively different resources, but that the attraction to resource density is constrained by an optimum after which attraction decreases. Furthermore, in heterogeneous environments, flies showed a strong preference towards the more apparent resource, leading to AS for the more apparent resources and AR for the less apparent resource. The strength of this interaction increased with a decreasing frequency of the more apparent resource. These results imply that D.melanogaster mainly selects patches at the level of individual resources. Consequently, when a patch contains qualitatively different resources, the more apparent resource will attract a higher number of flies than the less apparent resource irrespective of the frequency of the apparent resource within the patch. Our study shows that associational effects can be explained by determining the hierarchical level at which a consumer selects its resources. When a consumer selects resources at the individual level rather than at the patch level, our results can be used to explain the population dynamics of host plants and their associated consumers under field conditions.

Place, publisher, year, edition, pages
2016. Vol. 30, no 11, 1826-1833 p.
Keyword [en]
associational effects, attraction behaviour, complex environments, Drosophila melanogaster, frequency dependence, insect olfaction, neighbourhood effects, wind tunnel
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-136924DOI: 10.1111/1365-2435.12670ISI: 000387362600010OAI: oai:DiVA.org:su-136924DiVA: diva2:1061671
Available from: 2017-01-03 Created: 2016-12-19 Last updated: 2017-04-27Bibliographically approved
In thesis
1. Searching for food in complex environments: Integrating processes at multiple spatial scales
Open this publication in new window or tab >>Searching for food in complex environments: Integrating processes at multiple spatial scales
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Resources are often unevenly distributed through the environment, resulting in a challenging task for insects to locate food, mates and oviposition sites. Consequently, there is an ongoing need to unravel how insects rely on behavioural and sensory traits while searching for resources in heterogeneous environments. In the first part of this thesis, I addressed this issue by studying how neighbouring resources can affect the likelihood of insects finding their preferred host resources. These effects of neighbouring resources are commonly referred to as associational effects, and are expected to result from limitations in the sensory physiology of insects. Such limitations constrain the insect’s ability to correctly evaluate resource quality at the different steps involved in insect search behaviour. Furthermore, I determined whether the physiological state of an insect, and sensory experiences made during larval stages, can affect host search behaviour in heterogeneous environments.

By comparing the behaviour of Drosophila melanogaster in environments with single and multiple resources, I found that the presence of neighbouring recourses increased the selection rates for attractive resources, while it decreased the selection rates for less attractive resources. These effects are referred to as associational susceptibility and associational resistance respectively. Furthermore, by studying oviposition behaviour, I found that during these small-scale behavioural decisions, associational effects are mainly governed by gustatory mediated selection and less by olfactory mediated selection. The oviposition assay eliminated potential misinterpretations of resource quality along the different steps of search behaviour, hence the results suggested that associational effects rely on distinctive selection behaviour between resource types rather than on sensory constraints.

In the second part of this thesis I determined whether natal experiences can be used by insects as sensory shortcuts to find host resources, and whether this leads to better larval performance on those selected host resources. For this purpose, I studied the interactions between the larval parasitoid Asecodes lucens and the oligophagous leaf beetle Galerucella sagittariae. The results showed that the relationship between oviposition preference and larval performance, of both insect species, depends on an interactive effect between the insects’ natal origin and the quality of the different host resources. Moreover, I found that the natal origin was a better predictor for the adult host preference, rather than for larval performance. This suggests that, aside from the actual quality of the host resources, locating any suitable host might be even more limiting for the female’s fitness. 

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2017. 34 p.
Keyword
Associational effects, Natal experiences, Olfaction, Oviposition
National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-141762 (URN)978-91-7649-784-5 (ISBN)978-91-7649-785-2 (ISBN)
Public defence
2017-06-02, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, 09:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Submitted.

Available from: 2017-05-10 Created: 2017-04-16 Last updated: 2017-05-15Bibliographically approved

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