Showing papers by "Riccardo Bommarco published in 2012"

Insect pollination enhances seed yield, quality, and market value in oilseed rape

Abstract: The relationships between landscape intensification, the abundance and diversity of pollinating insects, and their contributions to crop yield, quality, and market value are poorly studied, despite observed declines in wild and domesticated pollinators. Abundance and species richness of pollinating insects were estimated in ten fields of spring oilseed rape, Brassica napus var. SW Stratos™, located along a gradient of landscape compositions ranging from simple landscapes dominated by arable land to heterogeneous landscapes with extensive cover of semi-natural habitats. In each field, we assessed the contribution of wind and insect pollination to seed yield, seed quality (individual seed weight and oil and chlorophyll contents), and market value in a block experiment with four replicates and two treatments: (1) all flowers were accessible to insects, self and wind pollination, and (2) flowers enclosed in tulle net bags (mesh: 1 × 1 mm) were accessible only to wind and self pollination. Complex landscapes enhanced the overall abundance of wild insects as well as the abundance and species richness of hoverflies. This did not translate to a higher yield, probably due to consistent pollination by honey bees across all fields. However, the pollination experiment showed that insects increased seed weight per plant by 18% and market value by 20%. Seed quality was enhanced by insect pollination, rendering heavier seeds as well as higher oil and lower chlorophyll contents, clearly showing that insect pollination is required to reach high seed yield and quality in oilseed rape. Our study demonstrates considerable and previously underestimated contributions from pollinating insects to both the yield and the market value of oilseed rape.

Drastic historic shifts in bumble-bee community composition in Sweden

Abstract: The species richness of flower-visiting insects has declined in past decades, raising concerns that the ecosystem service they provide by pollinating crops and wild plants is threatened. The relative commonness of different species with shared ecological traits can play a pervasive role in determining ecosystem functioning, but information on changes in abundances of pollinators over time is lacking. We gathered data on relative abundances of bumble-bee species in Swedish red clover fields during three periods in the last 70 years (1940s, 1960s and present), and on clover seed yields since 1921. We found drastic decreases in bumble-bee community evenness, with potential consequences for level and stability of red clover seed yield. The relative abundances of two short-tongued bumble-bees have increased from 40 per cent in the 1940s to entirely dominate present communities with 89 per cent. Average seed yield declined in recent years and variation in yield doubled, suggesting that the current dependence on few species for pollination has been especially detrimental to stability in seed yield. Our results suggest a need to develop management schemes that promote not only species-rich but also more evenly composed communities of service-providing organisms.

Landscape matrix modifies richness of plants and insects in grassland fragments

Abstract: There is an increasing awareness that not only area and isolation, but also the characteristics of the landscape surrounding habitat patches influence population persistence and species diversity i ...

Effect of habitat area and isolation on plant trait distribution in European forests and grasslands

Abstract: A number of studies show contrasting results in how plant species with specific life-history strategies respond to fragmentation, but a general analysis on whether traits affect plant species occurrences in relation to habitat area and isolation has not been performed. We used published data from forests and grasslands in north-central Europe to analyse if there are general patterns of sensitivity to isolation and dependency of area for species using three traits: life-span, clonality, and seed weight. We show that a larger share of all forest species was affected by habitat isolation and area as compared to grassland species. Persistence-related traits, life-span and clonality, were associated to habitat area and the dispersal and recruitment related trait, seed weight, to isolation in both forest and grassland patches. Occurrence of clonal plant species decreased with habitat area, opposite to non-clonal plant species, and long-lived plant species decreased with grassland area. The directions of these responses partly challenge some earlier views, suggesting that further decrease in habitat area will lead to a change in plant species community composition, towards relatively fewer clonal and long-lived plants with large seeds in small forest patches and fewer clonal plants with small seeds in small grassland patches. It is likely that this altered community has been reached in many fragmented European landscapes consisting of small and isolated natural and semi-natural patches, where many non-clonal and short-lived species have already disappeared. Our study based on a large-scale dataset reveals general and useful insights concerning area and isolation effects on plant species composition that can improve the outcome of conservation and restoration efforts of plant communities in rural landscapes.

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

Abstract: 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.

Traits related to species persistence and dispersal explain changes in plant communities subjected to habitat loss

Abstract: Aim Habitat fragmentation is a major driver of biodiversity loss but it is insufficiently known how much its effects vary among species with different life-history traits; especially in plant communities, the understanding of the role of traits related to species persistence and dispersal in determining dynamics of species communities in fragmented landscapes is still limited. The primary aim of this study was to test how plant traits related to persistence and dispersal and their interactions modify plant species vulnerability to decreasing habitat area and increasing isolation. Location Five regions distributed over four countries in Central and Northern Europe. Methods Our dataset was composed of primary data from studies on the distribution of plant communities in 300 grassland fragments in five regions. The regional datasets were consolidated by standardizing nomenclature and species life-history traits and by recalculating standardized landscape measures from the original geographical data. We assessed the responses of plant species richness to habitat area, connectivity, plant life-history traits and their interactions using linear mixed models. Results We found that the negative effect of habitat loss on plant species richness was pervasive across different regions, whereas the effect of habitat isolation on species richness was not evident. This area effect was, however, not equal for all the species, and life-history traits related to both species persistence and dispersal modified plant sensitivity to habitat loss, indicating that both landscape and local processes determined large-scale dynamics of plant communities. High competitive ability for light, annual life cycle and animal dispersal emerged as traits enabling species to cope with habitat loss. Main conclusions In highly fragmented rural landscapes in NW Europe, mitigating the spatial isolation of remaining grasslands should be accompanied by restoration measures aimed at improving habitat quality for low competitors, abiotically dispersed and perennial, clonal species.

Towards Integrated Pest Management in Red Clover Seed Production

Abstract: The development of integrated pest management is hampered by lack of information on how insect pest abundances relate to yield losses, and how pests are affected by control measures. In this study, we develop integrated pest management tactics for Apion spp. weevils (Coleoptera: Brentidae) in seed production of red clover, Trifolium pratense L. We tested a method to forecast pest damage, quantified the relationship between pest abundance and yield, and evaluated chemical and biological pest control in 29 Swedish red clover fields in 2008 and 2011. Pest inflorescence abundance, which had a highly negative effect on yield, could be predicted with pan trap catches of adult pests. In 2008, chemical control with typically one application of pyrethroids was ineffective both in decreasing pest abundances and in increasing yields. In 2011, when chemical control included applications of the neonicotinoid thiacloprid, pest abundances decreased and yields increased considerably in treated field zones. A post hoc analysis indicated that using pyrethroids in addition to thiacloprid was largely redundant. Infestation rates by parasitoids was higher and reached average levels of around 40% in insecticide treated field zones in 2011, which is a level of interest for biological pest control. Based on the data presented, an economic threshold for chemical control is developed, and guidelines are provided on minimum effective chemical pest control.

High mobility reduces beta-diversity among orthopteran communities – implications for conservation

Abstract: . 1. The analysis of β-diversity, i.e. species turnover, across space is central to a wide array of ecological and evolutionary topics, also providing critical information to conservation planning. Although dispersal limitation has been demonstrated to play an important role in determining insect community structure, very little research has been done to test whether mobility might affect the diversity distribution of species across multiple spatial scales. 2. We considered orthopterans (Ensifera and Caelifera) inhabiting hay meadows to test whether species mobility modifies β-diversity patterns across three nested spatial scales (1-m2 plots within meadow, 1000-m2 meadows within landscape, and 19.6-km2 landscapes within a region) and along a gradient of management intensity. 3. Orthopteran community composition varied most significantly over broader spatial scales. Larger proportion of regional γ-diversity was mainly composed of β-diversity at the landscape scale, whereas this proportion was smaller at the plot and meadow scale. 4. Mobility, but not management, strongly modified β-diversity patterns. Sedentary species contributed to a greater proportion of β-diversity across all the investigated scales compared with mobile species. 5. Measures currently included in most agri-environment schemes have only focused on the extensive management at the field scale. Our results imply that orthopteran diversity would benefit from maintaining extensively managed meadows scattered throughout the whole region, as the loss of species-rich isolated grassland patches due to abandonment or eutrophication might cause severe reductions of the regional species pool. Increasing connectivity might be also considered as a complementary measure to increase species occupancy and population persistence, particularly for sedentary species.

Växtskyddsmedlens påverkan på biologisk mångfald i jordbrukslandskapet

Abstract: Jordbrukslandskapet ar en viktig livsmiljo for ungefar halften av Europas vaxter och djur. Bevarande av biologisk mangfald i odlingslandskapet innebar bland annat att viktiga ekosystemtjansterar bibehalls. Pollinerande insekter och naturliga fiender till skadegorare ar exempel pa organismer som utgor en betydande resurs i jordbruket av stor ekonomisk betydelse. Kunskap om hur jordbruksatgarder, till exempel anvandningen av vaxtskyddsmedel, paverkar de organismer som finns i landskapetderder, ar darfor viktig. I denna rapport sammanstalls befintlig kunskap om hur landlevande biologisk mangfald, framst vaxter, insekter, faglar och daggdjur, paverkas av de tre vanligast typerna av vaxtskyddsmedel (ogras-, insekts- och svampmedel) som anvands i jordbruket i Sverige. Rapporten ar framst grundad pa studier som utforts i Europa och Nordamerika, eftersom det finns mycket lite svensk forskning om detta. Manga lander rapporterar en minskande biologisk mangfald i jordbrukslandskapet vilket huvudsakligen antas bero pa ett alltmer intensivt jordbruk. Anvandningen av kemiska vaxtskyddsmedel anges ofta som en viktig bidragande faktor, men den specifika effekten av vaxtskyddsmedelsanvandning ar i de flesta fall svar att urskilja fran andra forandringar som skett samtidigt, till exempel en forandrad markanvandning. En oversikt av anvandningen av vaxtskyddsmedel visar att det totala antalet hektardoser som anvands i Sverige har sedan slutet av 1990-talet legat pa en relativt konstant niva. Eftersom den odlade ytan av grodor dar vaxtskyddsmedel anvands sjunkit under samma tidsperiod finns det en trend att antalet behandlingar per hektar okat nagot under de senaste 15 aren. Anvandningen ar koncentrerad till Skane och andra slattbygdsomraden, och det ar mycket vanligare med anvandning av vaxtskyddsmedel pa stora an pa sma brukningsenheter. De flesta studierna av vaxtskyddsmedlens paverkan pa icke-malorganismer har undersokt dodliga effekter pa individniva i laboratoriemiljo. Kunskap saknas darfor om icke-dodliga (subletala) effekter pa till exempel individers livslangd och fertilitet. Dessutom saknas kunskap om vaxtskyddsmedlens effekter pa populationsprocesser och organismsamhallen. Befintliga studier indikerar att dagens vaxt har farre direkt dodliga effekter pa icke-malorganismer jamfort med de aldre preparat som de ersatt. Farre daggdjur och faglar forgiftas av vaxtskyddsmedel och det finns inte nagra rapporter om att dagens preparat skulle anrikas i naringskedjan. Det finns daremot dokumenterad paverkan pa icke-malorganismer aven vid anvandning av moderna vaxtskyddsmedel. Ofta ar dessa organismer nara beslaktade med skadegoraren. Exempel pamer detta ar att pollinerande insekter och naturliga fiender till skadegorare paverkas av insektsmedel. Ett annat exempel ar paverkan pa andra vaxter an ogras av ograsmedel. Det finns ocksa pavisade indirekta effekter av vaxtskyddsmedel som gett forandringar i organismsamhallen och en minskad biologisk mangfald. Detta har skett genom en minskad fodotillgang for vaxt- eller insektsatare, eller genom forandrade konkurrensforhallanden mellan arter. Exempel visar ocksa att ekosystemtjansterna biologisk kontroll och pollinering kan paverkas negativt av vaxtskyddsmedelsanvandning. Kombinationer av preparat kan forandra giftigheten for organismen, men konsekvenserna av detta for den biologiska mangfalden ar daligt kanda. Dessutom har det visats att exponering for vaxtskyddsmedel kan oka djurs och vaxters kanslighet for sjukdomar. Det framgar av denna litteraturgenomgang att det finns betydande kunskapsluckor, och att mer forskning behovs pa effekter av vaxtskyddsmedel pa landlevande biologisk mangfald och de tjanster de levererar. Overvakningen av bade biologisk mangfald och av anvandningen av vaxtskyddsmedel i olika delar av Sverige kan forbattras. Forebyggande och alternativa metoder samt teknikutveckling inom vaxtskyddet kan minska de mojliga riskerna for biologisk mangfald. Slutligen kan atgarder som gynnar biologisk mangfald i jordbrukslandskapet buffra for de negativa effekter som anvandningen av vaxtskyddsmedel kan ha.