Thomas Merckx

Urbanization drives community shifts towards thermophilic and dispersive species at local and landscape scales

The increasing conversion of agricultural and natural areas to human-dominated urban landscapes is predicted to lead to a major decline in biodiversity worldwide. Two conditions that typically differ between urban environments and the surrounding landscape are increased temperature, and high patch isolation and habitat turnover rates. However, the extent and spatial scale at which these altered conditions shape biotic communities through selection and/or filtering on species traits are currently poorly understood. We sampled carabid beetles at 81 sites in Belgium using a hierarchically nested sampling design wherein three local-scale (200xa0×xa0200xa0m) urbanization levels were repeatedly sampled across three landscape-scale (3xa0×xa03xa0km) urbanization levels. First, we showed that communities sampled in the most urbanized locations and landscapes displayed a distinct species composition at both local and landscape scale. Second, we related community means of species-specific thermal preferences and dispersal capacity (based on European distribution and wing morphology, respectively) to the urbanization gradients. We showed that urban communities consisted on average of species with a preference for higher temperatures and with better dispersal capacities compared to rural communities. These shifts were caused by an increased number of species tolerating higher temperatures, a decreased richness of species with low thermal preference, and an almost complete depletion of species with very low-dispersal capacity in the most urbanized localities. Effects of urbanization were most clearly detected at the local scale, although more subtle effects could also be found at the scale of entire landscapes. Our results demonstrate that urbanization may fundamentally and consistently alter species composition by exerting a strong filtering effect on species dispersal characteristics and favouring replacement by warm-dwelling species.

The Urban Heat Island and its spatial scale dependent impact on survival and development in butterflies of different thermal sensitivity

Abstract Climate alteration is one of the most cited ecological consequences of urbanization. However, the magnitude of this impact is likely to vary with spatial scale. We investigated how this alteration affects the biological fitness of insects, which are especially sensitive to ambient conditions and well‐suited organisms to study urbanization‐related changes in phenotypic traits. We monitored temperature and relative air humidity in wooded sites characterized by different levels of urbanization in the surroundings. Using a split‐brood design experiment, we investigated the effect of urbanization at the local (i.e., 200 × 200 m) and landscape (i.e., 3 × 3 km) scale on two key traits of biological fitness in two closely related butterfly species that differ in thermal sensitivity. In line with the Urban Heat Island concept, urbanization led to a 1°C increase in daytime temperature and an 8% decrease in daytime relative humidity at the local scale. The thermophilous species Lasiommata megera responded at the local scale: larval survival increased twofold in urban compared to rural sites. Urbanized sites tended to produce bigger adults, although this was the case for males only. In the woodland species Pararge aegeria, which has recently expanded its ecological niche, we did not observe such a response, neither at the local, nor at the landscape scale. These results demonstrate interspecific differences in urbanization‐related phenotypic plasticity and larval survival. We discuss larval pre‐adaptations in species of different ecological profiles to urban conditions. Our results also highlight the significance of considering fine‐grained spatial scales in urban ecology.

Body-size shifts in aquatic and terrestrial urban communities

Body size is intrinsically linked to metabolic rate and life-history traits, and is a crucial determinant of food webs and community dynamics1,2. The increased temperatures associated with the urban-heat-island effect result in increased metabolic costs and are expected to drive shifts to smaller body sizes3. Urban environments are, however, also characterized by substantial habitat fragmentation4, which favours mobile species. Here, using a replicated, spatially nested sampling design across ten animal taxonomic groups, we show that urban communities generally consist of smaller species. In addition, although we show urban warming for three habitat types and associated reduced community-weighted mean body sizes for four taxa, three taxa display a shift to larger species along the urbanization gradients. Our results show that the general trend towards smaller-sized species is overruled by filtering for larger species when there is positive covariation between size and dispersal, a process that can mitigate the low connectivity of ecological resources in urban settings5. We thus demonstrate that the urban-heat-island effect and urban habitat fragmentation are associated with contrasting community-level shifts in body size that critically depend on the association between body size and dispersal. Because body size determines the structure and dynamics of ecological networks1, such shifts may affect urban ecosystem function.The urban-heat-island effect drives community-level shifts towards smaller body sizes; however, habitat fragmentation caused by urbanization favours larger body sizes in species with positive size–dispersal links.

Rewilding : Pitfalls and Opportunities for Moths and Butterflies

Small organisms provide the bulk of biodiversity. Here, we look at rewilding from their perspective. As an umbrella group for other terrestrial invertebrates, we focus on the diverse group of Lepidoptera. More specifically, we set out to explore their response to farmland abandonment. So far, studies have warned against farmland abandonment, which is for instance listed as one of the key threats to European butterfly diversity. Here, partly based on a case study within the Peneda mountain range, we argue (i) that the majority of Lepidoptera is to a greater or lesser extent forest-dependent, (ii) that effects on species composition should be considered at regional rather than smaller scales, and (iii) that habitat resource heterogeneity at multiple spatial scales is key. As such, we believe that rewilding does offer opportunities to Lepidoptera. However, we recommend rewilding not to be equalled to a hands-off approach, but rather to a goal-driven conservation management approach. It should monitor, and where necessary intervene to provide habitat heterogeneity at multiple spatial scales, in order to cater for the whole gradient of sedentary to mobile species. Given that sufficient levels of habitat heterogeneity are maintained, Lepidoptera are one of probably many taxa that are likely to benefit from rewilding processes on European marginal farmland. The resulting improved species composition will help achieve European species conservation targets. It may also lead to more viable populations of moths, butterflies and other invertebrates, which will foster more resilient food-webs and increased ecosystem functioning.

Anthropogenic host plant expansion leads a nettle-feeding butterfly out of the forest: consequences for larval survival and developmental plasticity in adult morphology

Recent anthropogenic eutrophication has meant that host plants of nettle‐feeding insects became quasi‐omnipresent in fertile regions of Western Europe. However, host plant resource quality – in terms of microclimate and nutritional value – may vary considerably between the ‘original’ forest habitat and ‘recent’ agricultural habitat. Here, we compared development in both environmental settings using a split‐brood design, so as to explore to what extent larval survival and adult morphology in the nettle‐feeding butterfly Aglais urticae are influenced by the anthropogenic environment. Nettles along field margins had higher C/N ratios and provided warmer microclimates to larvae. Larvae developed 20% faster and tended to improve their survival rates, on the agricultural land compared to woodland. Our split‐brood approach indicated plastic responses within families, but also family effects in the phenotypic responses. Adult males and females had darker wing pigmentation in the drier and warmer agricultural environment, which contrasts with the thermal melanism hypothesis. Developmental plasticity in response to this microclimatically different and more variable habitat was associated with a broader phenotypic parameter space for the species. Both habitat expansion and developmental plasticity are likely contributors to the ecological and evolutionary success of these nettle‐feeding insects in anthropogenic environments under high nitrogen load.

High impact journals in ecology cover proportionally more statistically significant findings

Unbiased scientific reporting is crucial for data and research synthesis. Previous studies suggest that statistically significant results are more likely to be published and more likely to be submitted to high impact journals. However, the most recent research on statistical significance in relation to journal impact factors in ecological research was published more than two decades ago or addressed a small subset of the literature. Here, we extract p-values from all articles published in 11 journals in 2012 and 2014 across a wide range of impact factors with six journals sampled in both years. Our results indicate that the proportion of statistically significant results increases with rising impact factor. Such a trend can have important consequences for syntheses of ecological data and it highlights the importance of covering a wide range of impact factors when identifying published studies for data syntheses. This trend can also lead to a biased understanding of the probability of true effects in ecology and conservation. We caution against the possible downplaying of non-significant results by either journals or authors.