Based on both ecological and phytochemical measures, we have identified bottom-up forces (host plant quality) as a relatively weak force in determining what plant-eating insects occur where in the landscape. As an alternative, we have examined the potential for top-down influences (natural enemies) to directly exclude herbivore species from given sites, but found this force insufficient, too. Rather than external influences, we have therefore proposed spatially structured population processes within species as the driver of patterns observed at the landscape level. We have supported this conclusion by mathematical models built on simple assumptions regarding the behaviour of individual insects in patchy landscapes. Such models are able to explain a significant part of empirically observed patterns of occurrence and colonization. In the next phase of the project, we extended current models of single species to spatial models of the full herbivore community.
Work in the oak system has largely centered on two PhD projects exploring different aspects of multitrophic interactions. Then-student Ayco Tack examined the extent to which local horizontal interactions on the one hand and spatial processes on the other will structure local communities of oak-specific herbivores. Through a series of field experiments, he quantified both direct and indirect competition among leaf-mining herbivores, and dispersal in ten different species co-occurring on Q. robur. Ayco continues with oak work, see here.
In her thesis, Riikka Kaartinen focused on effects of landscape structure on top-down interactions. Ambitiously, she constructed quantitative food webs for over 30 individual oak trees of varying isolation, thereby exploring the extent to which spatial connectivity (and hence habitat fragmentation) may affect the structure of local communities.
In 2016, we conducted a citizen survey of oak-associated insect communities in Sweden. More information (in Swedish) available here.
For more information on our main study site, click here. Very much of this work has been conducted in collaboration with Dr Sofia Gripenberg, (a former graduate from our group), Dr Juha-Pekka Salminen at the University of Turku and Prof Otso Ovaskainen (MRG).