Aim  We compare the influence of contemporary geography and historical influences on butterfly diversity for islands in the Aegean archipelago. Location  The Aegean archipelago (Greece) and two islands (Cyprus and Megisti) in the Levantine Sea. Methods  Thirty‐one islands were examined. Data are taken from own surveys (Coutsis and Olivier) and from the literature. Stepwise multiple regression is used to determine relationships between species richness, frequency, rarity and endemicity against potential geographical predictors. Stepwise logit regression is used to determine geographical predictors of species incidence on islands. Inter‐island and inter‐species associations have been examined using multivariate ordination and clustering techniques. Results  The Aegean butterfly fauna is characterized by decreasing diversity and rarity, and increasing homogeneity, from the periphery to the present geographical centre of the archipelago (Cyclades). Diversity and rarity are shown to relate closely to species richness, and species richness, in turn, is largely explained by contemporary geography, particularly the degree of isolation from the nearest mainland sources of Greece or Turkey, and island dimensions. Islands towards the centre of the archipelago are characterized by a group of mobile species (n ≥ 20 species) with extensive ranges across Europe; species that would have recolonized Santorini (Thira) following the VI6 eruption there c. 1630 bc. Endemic components, indicative of autochthonous evolutionary events, are few (5% of species are endemic) compared to known sedentary organisms (molluscs and isopods), but exceed those for more mobile animals (i.e. birds); their distribution is mainly confined to large isolated islands along the Aegean arc (i.e. Kriti) and in the Dodecanese group. Main conclusions  Contemporary geography, i.e. processes currently operating in ecological time, dominates butterfly diversity gradients (species richness, frequency, rarity and incidence) in the archipelago. Two reasons are suggested to account for the lack of endemism and the pattern of decreasing diversity into the Cyclades. First, relict butterfly elements may have become extinct on all but a few larger islands, particularly from environmental changes since the Neolithic (fire and overgrazing). Second, colonization from the continental landmasses is ongoing with more mobile species transferring even to the most isolated islands.

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Land use affects the carbon sequestration potential of soils across landscapes. Tree-based intercropping (TBI) systems where annual crops are grown between established tree rows are expected to exhibit spatial heterogeneity in the soil organic carbon (SOC) content due to differences in carbon input and decomposition rates of litter from trees and herbaceous plants. This study aimed to quantify variability in the SOC of TBI systems, compare the SOC content of TBI and nearby conventional agroecosystems, and determine if SOC was related to soil fertility. The TBI research sites were established 4 years (St. Paulin and St. Edouard, Quebec, Canada), 8 years (St. Remi, Quebec, Canada) and 21 years (Guelph, Ontario, Canada) before soil samples were collected for this study. The SOC content was greater within 0.75 m of the tree row than in the intercropped space at the St. Edouard and St. Remi sites. At the Guelph site, the SOC was spatially heterogeneous in plots with Norway spruce (Picea abies L.) but not hybrid poplar (Populus deltoides 9 P. nigra clone DN-177), probably due to litterfall distribution. Formerly a tree plantation, the TBI system at St. Remi contained 77% more SOC than a nearby conventional agroecosystem, while there was 12% more SOC in the TBI system than the conventional agroecosystem at Guelph. There was no difference in the SOC content of 4-year old TBI sites and nearby conventional agroecosystems. However, an increase in SOC at all TBI sites was positively related to the plant-available N concentrations, indicating the benefit of temperate TBI systems for soil fertility.

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Cell surface interactions between sorghum roots and the parasitic weed Striga hermonthica were investigated using light and electron microscopy. An exoglucanase–gold complex was used to study the distribution of cellulose in host tissues of resistant and susceptible cultivars. In the susceptible cultivar, intrusive cells of S. hermonthica could reach xylem elements, whereas in the resistant cultivar, development occurred mainly in the outer cortex. Invasion of the susceptible cultivar was accompanied by wall alterations and by the release of cellulose-rich fragments likely detached from host walls through the action of lytic enzymes. The occurrence of wall alterations at a short distance from the point of parasite penetration provided indirect evidence for extracellular diffusion of cellulolytic enzymes. Tylose formation and accumulation of coating material along secondary thickenings of some xylem vessels were late responses observed in the susceptible cultivar. In the resistant cultivar, heavy deposition of successive layers of cellulosic material occurred in outer tissues. Accumulation of this material may constitute a defense reaction against penetration. Electron-dense coating material was noticeable in cortical cells and occasionally in xylem vessels. Defense reactions observed in both sorghum cultivars upon parasite attack differed in their temporal and spatial distribution. Key words: Striga, sorghum, haustorium, root anatomy, gold cytochemistry, cellulose, resistance.

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