Markus Franzén

The landscape matrix modifies the effect of habitat fragmentation in grassland butterflies

The landscape matrix is suggested to influence the effect of habitat fragmentation on species richness, but the generality of this prediction has not been tested. Here, we used data from 10 independent studies on butterfly species richness, where the matrix surrounding grassland patches was dominated by either forest or arable land to test if matrix land use influenced the response of species richness to patch area and connectivity. To account for the possibility that some of the observed species use the matrix as their main or complementary habitat, we analysed the effects on total species richness and on the richness of grassland specialist and non-specialist (generalists and specialists on other habitat types) butterflies separately. Specialists and non-specialists were defined separately for each dataset. Total species richness and the richness of grassland specialist butterflies were positively related to patch area and forest cover in the matrix, and negatively to patch isolation. The strength of the species-area relationship was modified by matrix land use and had a slope that decreased with increasing forest cover in the matrix. Potential mechanisms for the weaker effect of grassland fragmentation in forest-dominated landscapes are (1) that the forest matrix is more heterogeneous and contains more resources, (2) that small grassland patches in a matrix dominated by arable land suffer more from negative edge effects or (3) that the arable matrix constitutes a stronger barrier to dispersal between populations. Regardless of the mechanisms, our results show that there are general effects of matrix land use across landscapes and regions, and that landscape management that increases matrix quality can be a complement to habitat restoration and re-creation in fragmented landscapes.

Both population size and patch quality affect local extinctions and colonizations

Currently, the habitat of many species is fragmented, resulting in small local populations with individuals occasionally dispersing between the remaining habitat patches. In a solitary bee metapopulation, extinction probability was related to both local bee population sizes and pollen resources measured as host plant population size. Patch size, on the other hand, had no additional predictive power. The turnover rate of local bee populations in 63 habitat patches over 4 years was high, with 72 extinction events and 31 colonization events, but the pollen plant population was stable with no extinctions or colonizations. Both pollen resources and bee populations had strong and independent effects on extinction probability, but connectivity was not of importance. Colonizations occurred more frequently within larger host plant populations. For metapopulation survival of the bee, large pollen plant populations are essential, independent of current bee population size.

Long-term land-use changes and extinction of specialised butterflies

Abstract.  1 Land‐use change in 450 ha in southern Sweden between 1814 and 2004 was recorded. Butterflies and burnet moths were surveyed in 1904–1913 and 2001–2005. 2 We explore if local extinctions were related to land‐use changes and species attributes. 3 Land use changed drastically over the 190‐year period, and the largest relative change occurred for hay meadows with late harvest, which decreased from 28% to 0%. The area changed from grasslands and grazed forests to being dominated by timber forests. Previous open grazed mixed woodlands changed to spruce plantations with clear‐cuts. 4 Of the 48 resident butterfly and burnet moths found a century ago, 44% have become extinct. The extinct Aporia cratægi, Colias palaeno, and Leptidea sinapis were abundant 100 years ago and had their highest densities in flower‐rich glades in forest, a habitat which no longer exists. 5 The butterfly extinctions could be predicted from species‐specific attributes as a short flight length period (P < 0.02), narrow habitat breadth (P < 0.02), small distribution area in Europe (P = 0.033) and possibly larvae food plant nitrogen class (P < 0.06). In a multiple logistic regression, the flight length period was the only significant variable because the independent variables were intercorrelated. 6 We conclude that the most important factor explaining the high extinction rate is that flower‐rich habitats have disappeared from both woodlands as well as from open farmlands. The most sensitive species are specialised species with a short summer flight which have gone extinct. Only the most unspecialised species still persist in the current landscape.

With that diet, you will go far : trait-based analysis reveals a link between rapid range expansion and a nitrogen-favoured diet.

Recent global change has had a substantial influence on the distribution of organisms, and many species are currently expanding their ranges. To evaluate the underlying processes, long-term data with good geographic resolution are essential. One important but generally overlooked data source is offered by the taxon-specific national catalogues of first provincial records that are kept in many countries. Here, we use such data to quantify trait-based influences on range expansion in Swedish butterflies and moths between 1973 and 2010. Of 282 species meeting pre-defined quality criteria, 170 expanded their northern range margin, with a mean expansion rate of 2.7 km per year. The analyses demonstrate that habitat and diet generalists, forest species and species active during warm conditions have expanded their ranges more rapidly than other species. Notably, range expansion in diet specialists was positively related to a nitrogen-favoured larval diet, an effect not found among oligo- or polyphagous species. In contrast to the general view, this shows that specialist species can undergo rapid range expansion. We suggest that increased areas of nitrogen-rich habitat, and increased availability of a nitrogen-favoured diet, are among the most important drivers of range expansions, potentially having far-reaching consequences for a wide variety of organisms.

Species-Area Relationships Are Controlled by Species Traits

The species-area relationship (SAR) is one of the most thoroughly investigated empirical relationships in ecology. Two theories have been proposed to explain SARs: classical island biogeography theory and niche theory. Classical island biogeography theory considers the processes of persistence, extinction, and colonization, whereas niche theory focuses on species requirements, such as habitat and resource use. Recent studies have called for the unification of these two theories to better explain the underlying mechanisms that generates SARs. In this context, species traits that can be related to each theory seem promising. Here we analyzed the SARs of butterfly and moth assemblages on islands differing in size and isolation. We tested whether species traits modify the SAR and the response to isolation. In addition to the expected overall effects on the area, traits related to each of the two theories increased the model fit, from 69% up to 90%. Steeper slopes have been shown to have a particularly higher sensitivity to area, which was indicated by species with restricted range (slope  = 0.82), narrow dietary niche (slope  = 0.59), low abundance (slope  = 0.52), and low reproductive potential (slope  = 0.51). We concluded that considering species traits by analyzing SARs yields considerable potential for unifying island biogeography theory and niche theory, and that the systematic and predictable effects observed when considering traits can help to guide conservation and management actions.

Mobility is related to species traits in noctuid moths

1. Mobility is important for the understanding of how species survive in fragmented landscapes and cope with increasing rates of habitat and climate change. However, mobility is a difficult trait to explore and is poorly known in most taxa. Species traits have been studied in relation to range shifts, extinction risks, and responses to habitat area and isolation, and have also been suggested as good estimators of mobility. Here we explore the relation between mobility and species traits in noctuid moths.

How threatened are alpine environments? a cross taxonomic study

Cold-adapted ecosystems are often considered to be stable, species poor, and well protected. However, such ecosystems have been identified as being especially sensitive to threats from global warming. Despite this, recent studies have found low proportions of Red Listed species in these systems. In this study we explored the number of alpine species (dependent on alpine habitats for their survival) and their Red List status in Sweden. We determined the proportion of Red Listed species and explored discrepancies among different groups of organisms in terms of the proportion of Red Listed species and the criteria used for Red Listing. We found a total of 389 alpine species in twelve analyzed species groups. The overall proportion of Red Listed species was 29%, with 15% regarded as threatened. There were substantial differences among taxonomic groups with respect to the proportion of Red Listed species. Among mammals 75% of the species are Red Listed, along with 63% of butterflies and 50% of birds. In addition the single alpine dragonfly species and all three alpine stinging wasp species are also Red Listed. Although beetles, bumblebees and grasshoppers are represented by a total of 17 alpine species, none are Red Listed. In contrast to previous studies, our results show that the proportion of Red Listed species is high in alpine environments, indicating that ecosystems found above the tree line are indeed threatened. No species in Sweden have been Red Listed on the basis of the IUCN criterion E (unfavorable quantitative analysis), this is surprising since entire cold-adapted ecosystems are likely to disappear in the future. We highlight the need for a better and more coordinated application of the IUCN criteria, as well as a more stringent strategy to assess the extinction risks for alpine species, thus maintaining reliable Red Lists.

High population variability and source–sink dynamics in a solitary bee species

Although solitary bees are considered to play key roles in ecosystem functions, surprisingly few studies have explored their population dynamics. We investigated the population dynamics of a rare, declining, solitary bee (Andrena humilis) in a landscape of 80 km2 in southern Sweden from 2003 to 2011. Only one population was persistent throughout all years studied; most likely this population supplied the surrounding landscape with 11 smaller, temporary local populations. Despite stable pollen availability, the size of the persistent population fluctuated dramatically in a two-year cycle over the nine years, with 490-1230 nests in odd-numbered years and 21-48 nests in even-numbered years. These fluctuations were not significantly related to climatic variables or pollen availability. Nineteen colonization and 14 extinction events were recorded. Occupancy decreased with distance from the persistent population and increased with increasing resource (pollen) availability. There were significant positive correlations between the size of the persistent population and patch occupancy and colonization. Colonizations were generally more common in patches closer to the persistent population, whereas extinctions were independent of distance from the persistent population. Our results highlight the complex population dynamics that exist for this solitary bee species, which could be due to source-sink dynamics, a prolonged diapause, or can represent a bet-hedging strategy to avoid natural enemies and survive in small habitat patches. If large fluctuations in solitary bee populations prove to be widespread, it will have important implications for interpreting ecological relationships, bee conservation, and pollination.

Functional traits help to explain half-century long shifts in pollinator distributions

Changes in climate and land use can have important impacts on biodiversity. Species respond to such environmental modifications by adapting to new conditions or by shifting their geographic distributions towards more suitable areas. The latter might be constrained by species’ functional traits that influence their ability to move, reproduce or establish. Here, we show that functional traits related to dispersal, reproduction, habitat use and diet have influenced how three pollinator groups (bees, butterflies and hoverflies) responded to changes in climate and land-use in the Netherlands since 1950. Across the three pollinator groups, we found pronounced areal range expansions (>53%) and modelled range shifts towards the north (all taxa: 17–22 km), west (bees: 14 km) and east (butterflies: 11 km). The importance of specific functional traits for explaining distributional changes varied among pollinator groups. Larval diet preferences (i.e. carnivorous vs. herbivorous/detritivorous and nitrogen values of host plants, respectively) were important for hoverflies and butterflies, adult body size for hoverflies, and flight period length for all groups. Moreover, interactions among multiple traits were important to explain species’ geographic range shifts, suggesting that taxon-specific multi-trait analyses are needed to predict how global change will affect biodiversity and ecosystem services.

Variable coloration is associated with dampened population fluctuations in noctuid moths

Theory and recent reviews state that greater genetic and phenotypic variation should be beneficial for population abundance and stability. Experimental evaluations of this prediction are rare, of short duration and conducted under controlled environmental settings. The question whether greater diversity in functionally important traits stabilizes populations under more complex ecological conditions in the wild has not been systematically evaluated. Moths are mainly nocturnal, with a large variation in colour patterns among species, and constitute an important food source for many types of organisms. Here, we report the results of a long-term (2003–2013) monitoring study of 115 100 noctuid moths from 246 species. Analysis of time-series data provide rare evidence that species with higher levels of inter-individual variation in colour pattern have higher average abundances and undergo smaller between-year fluctuations compared with species having less variable colour patterns. The signature of interspecific temporal synchronization of abundance fluctuations was weak, suggesting that the dynamics were driven by species-specific biotic interactions rather than by some common, density-independent factor(s). We conclude that individual variation in colour patterns dampens population abundance fluctuations, and suggest that this may partly reflect that colour pattern polymorphism provides protection from visually oriented predators and parasitoids.