Saproxylic species are linked to the amount and isolation of dead wood across spatial scales in a beech forest

ContextDead wood is a key habitat for saproxylicspecies, which are often used as indicators of habitatquality in forests. Understanding how the amount andspatial distribution of dead wood in the landscapeaffects saproxylic communities is therefore importantfor maintaining high forest biodiversity.ObjectivesWe investigated effects of the amountand isolation of dead wood on the alpha and betadiversity of four saproxylic species groups, with afocus on how the spatial scale influences results.MethodsWe inventoried saproxylic beetles, wood-inhabiting fungi, and epixylic bryophytes and lichenson 62 plots in the Sihlwald forest reserve in Switzer-land. We used GLMs to relate plot-level speciesrichness to dead wood amount and isolation on spatialscales of 20–200 m radius. Further, we used GDMs todetermine how dead wood amount and isolationaffected beta diversity.ResultsA larger amount of dead wood increasedbeetle richness on all spatial scales, while isolation hadno effect. For fungi, bryophytes and lichens this wasonly true on small spatial scales. On larger scales ofour study, dead wood amount had no effect, whilegreater isolation decreased species richness. Further,we found no strong consistent patterns explaining betadiversity

Ambient and substrate energy influence decomposer diversity differentially across trophic levels

The species-energy hypothesis predicts increasing biodiversity with increasing energy in ecosystems. Proxies for energy availability are often grouped into ambient energy (i.e., solar radiation) and substrate energy (i.e., non-structural carbohydrates or nutritional content). The relative importance of substrate energy is thought to decrease with increasing trophic level from primary consumers to predators, with reciprocal effects of ambient energy. Yet, empirical tests are lacking. We compiled data on 332,557 deadwood-inhabiting beetles of 901 species reared from wood of 49 tree species across Europe. Using host-phylogeny-controlled models, we show that the relative importance of substrate energy versus ambient energy decreases with increasing trophic levels: the diversity of zoophagous and mycetophagous beetles was determined by ambient energy, while non-structural carbohydrate content in woody tissues determined that of xylophagous beetles. Our study thus overall supports the species-energy hypothesis and specifies that the relative importance of ambient temperature increases with increasing trophic level with opposite effects for substrate energy

Ambient and substrate energy influence decomposer diversity differentially across trophic levels.

The species-energy hypothesis predicts increasing biodiversity with increasing energy in ecosystems. Proxies for energy availability are often grouped into ambient energy (i.e., solar radiation) and substrate energy (i.e., non-structural carbohydrates or nutritional content). The relative importance of substrate energy is thought to decrease with increasing trophic level from primary consumers to predators, with reciprocal effects of ambient energy. Yet, empirical tests are lacking. We compiled data on 332,557 deadwood-inhabiting beetles of 901 species reared from wood of 49 tree species across Europe. Using host-phylogeny-controlled models, we show that the relative importance of substrate energy versus ambient energy decreases with increasing trophic levels: the diversity of zoophagous and mycetophagous beetles was determined by ambient energy, while non-structural carbohydrate content in woody tissues determined that of xylophagous beetles. Our study thus overall supports the species-energy hypothesis and specifies that the relative importance of ambient temperature increases with increasing trophic level with opposite effects for substrate energy

Dormancy induction in female meadow brown butterflies Maniola nurag and M. jurtina

Auf Sardinien machen die Weibchen der beiden Schmetterlingsarten Maniola nurag und M. jurtina eine Sommerruhe. Sie legen erst im Herbst ihre Eier ab, da das Gras, von dem sich die Larven ernähren, während der Sommermonate vertrocknet ist. Die zwei Arten unterscheiden sich stark in ihrer Verbreitung: M. nurag ist endemisch auf Sardinien, M. jurtina kommt dagegen europaweit vor und Populationen aus kühleren Regionen durchlaufen normalerweise keine Dormanz im Sommer. Für univoltine Arten, zu denen auch M. nurag und M. jurtina gehören, ist es überlebenswichtig, den richtigen Zeitpunkt für die Eiablage zu finden. In dieser Studie wurde der Einfluss der Tageslänge und der Verfügbarkeit von frischem Gras als Futterquelle für die Raupen auf die Dormanz und das Eiablageverhalten untersucht. Ich erwartete, dass Langtag und das Fehlen von Gras (= Sommerbedingungen) eine Sommerruhe fördern und die Eiablage verzögern. Für das Experiment wurden 150 Weibchen aus Sardinien (M. nurag + M. jurtina) und Österreich (M. jurtina) gesammelt und in Klimaschränken unter drei verschiedenen Bedingungen gehalten: Langtag (LD = L16:D8) mit Gras, Langtag ohne Gras sowie Kurztag (SD = L11:D13) mit Gras. Langtag-Bedingungen hatten einen verlängernden Effekt auf die Dormanz der sardischen Weibchen: 72 Tage (LD) im Vergleich zu 24 (SD). Auch lebten sie länger: 117 Tage (LD) gegen 56 (SD), ein Weibchen lebte sogar acht Monate lang. Frisches Gras hatte keinen Effekt auf die Dormanz. Die österreichischen Schmetterlinge (M. jurtina) reagierten nicht auf die veränderten Bedingungen (Lebensdauer: 54 Tage, Dormanz: 16 Tage): sie verhielten sich wie sardische Kurztag-Weibchen. Ich folgere daher, dass die Sommerruhe der Maniola-Weibchen aus dem Mittelmeergebiet durch die Tageslänge induziert wird, während die Photoperiode keinen Effekt auf das Eiablageverhalten mitteleuropäischer Individuen hat.In Sardinia, adult females of the two butterfly species Maniola nurag and M. jurtina perform a reproductive summer dormancy, i.e. they do not oviposit before autumn. With this strategy they survive summer-drought during which grass, the caterpillar’s food resource, is scarce. While M. nurag is endemic on the island, M. jurtina is widespread over Europe and populations of climatically cooler regions usually do not perform an aestivation. In this study I investigate the influence of day length and the availability of fresh grass as a food resource for the offspring on dormancy induction and egg-laying strategy. I expected that long daylength and the lack of grass (=summer conditions) would promote aestivation and therefore delay egg deposition. For the experiment, 150 females were collected from Sardinia (M. nurag + M. jurtina) and Austria (M. jurtina) and kept under three controlled conditions: long-day (LD = L16:D8) with fresh grass, long-day without grass, and short-day (SD = L11:D13) with fresh grass. The long-day treatment prolonged dormancy of Sardinian females from a mean of 24d (SD) to 72d (LD). Concomitantly, average adult lifespan was extended from 56d (SD) to 117d (LD); one female butterfly actually lived for eight months. Fresh grass had no effect on reproductive dormancy. M. jurtina from Austria did not show a reaction to the different treatments (average lifespan: 54d, days until oviposition: 16d), they behaved similar to short-day females from Sardinia. I conclude that reproductive summer dormancy in Mediterranean Maniola butterflies is induced by long-day, while day length has no effect on the timing of egg-laying of Central European individuals

What prolongs a butterfly's life? Trade-offs between dormancy, fecundity and body size

<p>Egg laying-data of M. nurag and M. jurtina</p

Boxplot of size of discoidal cell for each population.

<p>band = median; box = interquartile range (IQR); whiskers = lowest/highest data points within 1.5 IQR; spots = outliers.</p

Boxplots of duration of dormancy (A), total number of eggs (B), life span (C), and reproductive period (D) across species and treatments.

<p>Long day (1) versus short day (2); red = <i>M. nurag</i> (N), green<i> = M. jurtina</i> from Sardinia (JM), blue = <i>M. jurtina</i> from Austria (JA); band = median; box = interquartile range (IQR); whiskers = lowest/highest data points within 1.5 IQR; spots = outliers.</p

Dead wood distributed in different-sized habitat patches enhances diversity of saproxylic beetles in a landscape experiment

1. Human intervention often alters the availability of habitat for biodiversity. The conservation of biodiversity therefore requires an optimized habitat management. In forests, dead wood represents one of the most important habitats and in boreal and temperate regions around 25% of forest species depend on it (= saproxylic species). Increasing the amount of dead wood in managed forests has thus become a policy objective, but there is no consensus on how to best distribute dead wood in space. 2. In a landscape experiment, we exposed freshly cut beech branches in bundles of different sizes (one, three, six and 12 branches) in the forest, representing newly created habitat patches to be colonized by saproxylic beetles. We investigated how species richness in a ‘single large’ branch bundle compares to that in ‘several small’ bundles (SLOSS debate). We further tested the effects of dead wood availability (amount and isolation) in the surrounding landscape (20–200 m) and environmental factors (temperature and light availability) on species richness, abundance and community composition. 3. The species richness of the pooled small bundles (1 + 3 + 6 = 10 branches) was as high as that of the large bundle (12 branches), despite having a smaller total surface, demonstrating the benefit of spatially dispersed habitat patches for total diversity. Also community composition differed and every bundle size yielded some unique species. Dead wood availability in the surrounding landscape had a minor effect in comparison. Our results further highlight the importance of microsite heterogeneity: species richness was related to light availability, and abundance and community composition were related to temperature. 4. Synthesis and applications: Larger amounts of dead wood harbour more saproxylic beetle species and the distribution of dead wood in patches of different sizes within the forest can promote the development of variable species communities. Combined, this results in a higher species diversity. In managed forests, where retained dead wood is often homogeneous in terms of size or tree species, increasing heterogeneity by distributing dead wood in the forest could foster higher diversity of saproxylic species.ISSN:0021-8901ISSN:1365-266

Relationship between life span and the total number of eggs in M. nurag (A) and M. jurtina (B).

<p>Relationship between life span and the total number of eggs in M. nurag (A) and M. jurtina (B).</p

Results of linear models showing the effects of day length, body size and species or population provenance on duration of dormancy and life span.

<p>Note: Sardinian females: N = 95, <i>M. jurtina</i>: N = 86; all values marked in bold remained significant at p<0.05 after application of a table-wide false-discovery rate correction.</p><p>Results of linear models showing the effects of day length, body size and species or population provenance on duration of dormancy and life span.</p