Landscape simplification weakens the association between terrestrial producer and consumer diversity in Europe
(Oral)
Matteo Dainese
, Lorenzo Marini
SEE PEER REVIEW
Land-use change is one of the primary drivers of species loss (1), yet little is known about its effect on other components of biodiversity that may be at risk (2). Here, we ask whether, and to what extent, landscape simplification, measured as the percentage of arable land in the landscape, disrupts the functional and phylogenetic association between primary producers and consumers. Across seven European regions, we inferred the potential associations (functional and phylogenetic) between host plants and butterflies in 561 seminatural grasslands. Local plant diversity showed a strong bottom-up effect on butterfly diversity in the most complex landscapes, but this effect disappeared in simple landscapes. The functional associations between plant and butterflies are, therefore, the results of processes that act not only locally but are also dependent on the surrounding landscape context. Similarly, landscape simplification reduced the phylogenetic congruence among host plants and butterflies indicating that closely related butterflies become more generalist in the resources used. These processes occurred without any detectable change in species richness of plants or butterflies along the gradient of arable land. The structural properties of ecosystems are experiencing substantial erosion, with potentially pervasive effects on ecosystem functions and future evolutionary trajectories. Loss of interacting species might trigger cascading extinction events and reduce the stability of trophic interactions, as well as influence the longer term resilience of ecosystem functions. From an applied perspective, conservation efforts might fail if we do not consider how landscape simplification affects the cross-trophic-level diversity associations in a local community (3). Conservation interventions aimed at restoring consumer diversity by enhancing local plant resources is likely to be more effective in regions where landscape simplification has been less marked. Therefore, we suggest that monitoring of the relationships between the diversities of these taxa can serve as an early warning signal of ecosystem health and conservation status (2). In conclusion, our novel approach reveals that other components of biodiversity are lost well before the species richness variation. Our measures of functional and phylogenetic associations across trophic levels, and how they change in response to landscape simplification, contribute to a growing understanding of the properties that determine ecosystem resilience.
(1) Newbold, T. et al. Global effects of land use on local terrestrial biodiversity. Nature 520, 45-50 (2015).
(2) Valiente-Banuet, A. et al. Beyond species loss: the extinction of ecological interactions in a changing world. Funct. Ecol. 29, 299-307 (2015).
(3) Harvey, E. et al. Bridging ecology and conservation: from ecological networks to ecosystem function. J. Appl. Ecol. 54, 371-379 (2017).
INTRO: The authors explore the effects of land use changes in Europe on ecosystem health, attempting to expand the discussion beyond the most commonly discussed consequences--such as species loss--to other outcomes. They choose to focus on how the conversion of natural landscapes into farmland impacts interactions among trophic levels. By examining interactions among host plants and butterflies in areas differing in their degree of landscape simplification, the authors find that simplification results in changes in the functional and phylogenetic relationships between these two species groups. Notably, these changes depend on the degree of simplification that has already occurred and do not necessarily coincide with changes in species richness (which may arise as landscape simplification progresses). The authors suggest that examining changes in ecological relationships, such as those among butterflies and their host plants, can give conservation biologists important insight into the future consequences of landscape simplification-and signal an opportunity to intervene early, before further damage is done.
MERITS: The authors present a novel approach to evaluating the health of ecosystems - by monitoring changes in functional relationships, rather than the more typical method of measuring species richness. This is especially exciting, as the authors observe that changes in functional relationships may act as an "early warning signal of ecosystem health," preceding the perhaps more irreversible changes in species richness associated with more severe environmental degradation; thus, taking this approach could provide conservation biologists with a chance to intervene earlier and more effectively. The abstract is very thorough and presents a compelling story that makes me want to attend the authors' conference presentation to learn more, particularly about the potential applications of their novel approach.
CRITIQUE: If anything, I would have been interested to hear a bit more detail about the findings of the study and more direct demonstration of how they build up to the authors' conclusions. If length is a concern, perhaps the balance could be shifted slightly more toward the findings and away from the discussion/conclusion section (saving more of that for the presentation). However, I found the abstract very compelling as is and felt encouraged to attend the conference presentation to learn more.
DISCUSSION: Again, I found the authors' approach to evaluating ecosystem health to be novel and promising, with great potential to serve as an effective tool to help conservation biologists decide when to intervene in a landscape. The authors focus on the interactions between the two trophic levels of primary producers and consumers. I would also be curious whether they have considered any effects on interactions within these levels. Specifically, they mention that "closely related butterflies become more generalist in the resources" they use in simplified landscapes. Perhaps it is beyond the scope of the current research, but I would be interested to learn how this might alter interactions among butterflies (e.g. through changes in competitive interactions, etc.) and how changes in interactions within a trophic level could further feed into the cascade of ecological degradation seen in simplified landscapes.
