El riesgo de depredación y la competencia intraespecífica alteran el comportamiento de dispersión de semillas por parte de roedores

Los roedores tienen un importante papel como dispersores/depredadores de bellotas en los bosques Mediterráneos de Quercus spp. Existe abundante información del efecto de factores intrínsecos de las semillas (tamaño, composición) en la selección de las bellotas por estos animales, mientras que la influencia de otros procesos como el riesgo de depredación o la competencia intraespecífica han estado mucho menos estudiados. En un bosque mixto de encina y roble en el Parque Natural de Collserola, se ha investigado el patrón de dispersión/depredación de bellotas por parte del ratón de campo (Apodemus sylvaticus) en función del riesgo de depredación por parte de jineta (Genetta genetta) y la competencia intraespecífica (mediante un experimento en el que estos factores se simulaban a partir de olores). Un censo previo determinó que la población de roedores presente en el área de estudio estaba formada principalmente por Apodemys sylvaticus. Éstos respondieron al tratamiento de olor pues se observó un retraso significativo en la manipulación de bellotas de jineta respecto a los otros dos tratamientos. Asimismo, respecto a la distancia de dispersión se observó que las bellotas del tratamiento con olor a ratón eran dispersadas a menor distancia, a una distancia intermedia las de jineta y a mayor distancia las del tratamiento control. En todos los tratamientos, las bellotas dispersadas a zonas de microhábitat abierto fueron menos depredadas. Este trabajo sugiere que el patrón espacio temporal de dipersión/depredación de bellotas en bosques de encina y roble puede tener una elevada complejidad, a la vez que subraya el interés de mantener la integridad de las redes tróficas por sus efectos directos e indirectos sobre las poblaciones de organismos situados a diferentes niveles.

The role of climatic tolerances and seed traits in reduced extinction rates of temperate polygonaceae.

The latitudinal diversity gradient (LDG) is one of the most striking and consistent biodiversity patterns across taxonomic groups. We investigate the species richness gradient in the buckwheat family, Polygonaceae, which exhibits a reverse LDG and is, thus, decoupled from dominant gradients of energy and environmental stability that increase toward the tropics and confound mechanistic interpretations. We test competing age and evolutionary diversification hypotheses, which may explain the diversification of this plant family over the past 70 million years. Our analyses show that the age hypothesis, which posits that clade richness is positively correlated with the ecological and evolutionary time since clade origin, fails to explain the richness gradient observed in Polygonaceae. However, an evolutionary diversification hypothesis is highly supported, with diversification rates being 3.5 times higher in temperate clades compared to tropical clades. We demonstrate that differences in rates of speciation, migration, and molecular evolution insufficiently explain the observed patterns of differential diversification rates. We suggest that reduced extinction rates in temperate clades may be associated with adaptive responses to selection, through which seed morphology and climatic tolerances potentially act to minimize risk in temporally variable environments. Further study is needed to understand causal pathways among these traits and factors correlated with latitude.

Estimating sex-specific dispersal rates with autosomal markers in hierarchically structured populations.

A recent study suggests that sex-specific dispersal rates can be quantitatively estimated on the basis of sex- and state-specific (pre- vs. postdispersal) F-statistics. In the present paper, we extend this approach to account for the hierarchical structure of natural populations, and we validate it through individual-based simulations. The model is applied to an empirical data set consisting of 536 individuals (males, females, and predispersal juveniles) of greater white-toothed shrews (Crocidura russula), sampled according to a hierarchical design and typed for seven autosomal microsatellite loci. From this dataset, dispersal is significantly female biased at the local scale (breeding-group level), but not at the larger scale (among local populations). We argue that selective pressures on dispersal are likely to depend on the spatial scale considered, and that short-distance dispersal should mainly respond to kin interactions (inbreeding or kin competition avoidance), which exert differential pressure on males and females.

Predicting future distributions of mountain plants under climate change: does dispersal capacity matter?

Many studies have investigated the impacts that climate change could potentially have on the distribution of plant species, but few have attempted to constrain projections through plant dispersal limitations. Instead, most studies published so far have been using the simplification of considering dispersal as either unlimited or null. However, depending on a species' dispersal capacity, landscape fragmentation, and the rate of climatic change, these assumptions can lead to serious over- or underestimation of a species' future distribution. To quantify the discrepancies between unlimited, realistic, and no dispersal scenarios, we carried out projections of future distribution over the 21st century for 287 mountain plant species in a study area of the Western Swiss Alps. For each species, simulations were run for four dispersal scenarios (unlimited dispersal, no dispersal, realistic dispersal and realistic dispersal with long-distance dispersal events) and under four climate change scenarios. Although simulations accounting for realistic dispersal limitations did significantly differ from those considering dispersal as unlimited or null in terms of projected future distribution, using the unlimited dispersal simplification nevertheless provided good approximations for species extinctions under more moderate climate change scenarios. Overall, simulations accounting for dispersal limitations produced, for our mountainous study area, results that were significantly closer to unlimited dispersal than to no dispersal. Finally, analyzing the temporal pattern of species extinctions over the entire 21st century showed that, due to the possibility of a large number of species shifting their distribution to higher elevation, important species extinctions for our study area might not occur before the 2080-2100 time periods.

Ursinia nana (Anthemideae, Asteraceae), and adventive from South Africa which is becoming naturalized in the Iberian Peninsula. Observations about its reproductive biology and fruit dispersal mechanism.

The presence of Ursinia nana, an Anthemideae of South-African origin which has been introduced into the NE Iberian Peninsula, is reported for the fi rst time in Europe. The data offered cover its precise location, morphology, chromosome number, ecology and a population census, as well as its life cycle, fl oral structure, reproductive biology and fruit dispersal mechanisms. Of special note are the clear predominance of autogamy (geitonogamy) over xenogamy as a reproductive system and the large number of fruits produced with high and immediate germinative capacity. These characteristics permit rapid colonization by the introduced species, which can become invasive. However, fruit predation by the ant Messor barbarus points to a natural mechanism that helps regulate population growth and makes biological control possible. Finally its possibilities of expansion in the colonized area and of naturalization in the NE Iberian Peninsula are assessed.

Building wood debris piles benefits avian seed dispersers in burned and logged Mediterranean pine forests

Salvage logging is a common practice carried out in burned forests worldwide, and intended to mitigate the economic losses caused by wildfires. Logging implies an additional disturbance occurring shortly after fire, although its ecological effects can be somewhat mitigated by leaving wood debris on site. The composition of the bird community and its capacity to provide ecosystem services such as seed dispersal offleshy-fruited plants have been shown to be affected by postfire logging. We assessedthe effects of the habitat structure resulting from different postfire management practices on the bird community, in three burned pine forests in Catalonia (western Mediterranean). For this purpose, we focused on the group of species that is responsible for seed dispersal, a process which takes place primarily during the winter in theMediterranean basin. In addition, we assessed microhabitat selection by seed disperser birds in such environments in relation to management practices. Our results showed a significant, positive relationship between the density of wood debris piles and the abundance of seed disperser birds. Furthermore, such piles were the preferredmicrohabitat of these species. This reveals an important effect of forest management on seed disperser birds, which is likely to affect the dynamics of bird-dependent seed dispersal. Thus, building wood debris piles can be a useful practice for the conservation of both the species and their ecosystem services, while also being compatible with timber harvesting

Phenology, fruit set and dispersal of Cordia multispicata Cham., an important weed shrub of abandoned pastures in eastern Amazonia

ABSTRACT - (Phenology, fruit set and dispersal of Cordia multispicata Cham., an important weed shrub of abandoned pastures in eastern Amazonia). The reproductive ecology of the distylous tropical shrub Cordia multispicata was studied in an abandoned pasture in Paragominas County , Pará state, Brazil. It is a common species in the Amazon basin where it occurs as a weed in open and disturbed habitats. C. multispicata has many flowers per inflorescence (85 ± 12) but 84% abort before fertilization. Flowering occurs throughout the year. Fruits are small, with a red fleshy pericarp (skin-pulp) attractive to birds. Fruit set is lower during the dry season (less than 30%) and higher during the rainy season when there are many visits of insects to the flowers. Fruiting has a peak between the end of the dry season and the middle of the rainy season. Nineteen bird species were observed foraging for the fruits of C. multispicata, and 79% of those species can be considered as potential dispersal agents. The efficient seed dispersal and aggregated spatial distribution associated with some characteristics of the dispersors greatly contributed to the success of this species in abandoned pastures of eastern Amazonia.

The seed coat as a modulator of seed-environment relationships in Fabaceae

The seed coat is one of the main determinants of seed germination, vigor and longevity potentials. It is also intimately associated with temporal and spatial dispersion of seed germination in a large number of plant species. The understanding of its properties and characteristics may explain, anticipate or even allow the modification of seed performance under certain environmental conditions. There is a growing volume of evidence associating seed coat characteristics to specific seed problems. For example, susceptibility to mechanical damage is related to lignin content of the seed coat, while seed longevity and tolerance to field weathering depends on seed coat integrity. Seed performance in many legumes has been associated with certain seed coat structures, such as the hilum, strophiole and micropyle. In soybean, permeability is also related with porosity, color, and cerosity, that affect seed vigor, storage potential, resistance to shrinking and fungi infection, and to susceptibility to imbibition damage. The understanding of these associations is necessary before genetic alterations through breeding for desirable characteristics and is fundamental for the development and improvement of seed pre-sowing treatments, production, handling and quality evaluation procedures, which may ultimately result in reduction of seed quality losses and increase the efficiency of agricultural production systems.

Harvesting of Protium heptaphyllum (Aubl.) March. seeds (Burseraceae) by the leaf-cutting ant Atta sexdens L. promotes seed aggregation and seedling mortality

The role played by leaf-cutting ants as seed dispersers of non-myrmecochorous plants remains poorly understood. Here we document the harvesting of Protium heptaphyllum (Aubl.) March. seeds (Burseraceae) by the leaf-cutting ant Atta sexdens L. and its consequences for (1) seed deposition pattern; (2) seed germination; and (3) seedling mortality. The study was carried out at Dois Irmãos, a 390 ha reserve of Atlantic forest, northeast Brazil. Ant-seed harvesting on the ground was detected in 18.5% of all fruiting trees and ants harvested 41.1% ± 19.7% of the seed crop (mean ± s). In average, ants piled seeds 3.4 ± 2.2 m away from the trunk of parent trees and seed density in these piles reached 128.8 ± 138.8 seeds 0.25 m² during the peak of seed discarding by ants. During a 13 month period, mean seedling mortality varied from 0.54% up to 10.6% in ant-made seed piles vs. 0.05-4.2% in control samples, what resulted in a total seedling mortality of 97.7% vs. 81%. Ants systematically cut seedling epicotyls, accounting for 55% of seedling mortality in seed piles, whereas only 14 seedlings (4.2%) were cut by ants in the control samples. Our results suggest that seed harvesting by A. sexdens (1) affects approximately 20% of fruiting P. heptaphyllum trees and their seed crops; (2) promotes short-distance seed dispersal and high levels of seed aggregation; and (3) reduces seedling survival beneath parents.

Identification of Albizia lebbeck seed coat chitin-binding vicilins (7S globulins) with high toxicity to the larvae of the bruchid Callosobruchus maculatus

Seed coat is a specialized maternal tissue that interfaces the embryo and the external environment during embryogenesis, dormancy and germination. In addition, it is the first defensive barrier against penetration by pathogens and herbivores. Here we show that Albizia lebbeck seed coat dramatically compromises the oviposition, eclosion and development of the bruchid Callosobruchus maculatus. Dietary supplementation of bruchid larvae with A. lebbeck seed coat flour causes severe weight loss and reduces survival. By means of protein purification, mass spectrometry and bioinformatic analyses, we show that chitin-binding vicilins are the main source of A. lebbeck tegumental toxicity to C. maculatus. At concentrations as low as 0.1%, A. lebbeck vicilins reduce larval mass from 8.1 ± 1.7 (mass of control larvae) to 1.8 ± 0.5 mg, which corresponds to a decrease of 78%. Seed coat toxicity constitutes an efficient defense mechanism, hindering insect predation and preventing embryo damage. We hypothesize that A. lebbeck vicilins are good candidates for the genetic transformation of crop legumes to enhance resistance to bruchid predation.

Response of soybean genotypes to the expression of green seed under temperature and water stresses

Soybeans grown under water stress associated with high temperatures during seed maturation and pre-harvest may produce green seed (GS) with expressive reduction in seed quality. The objectives of this study were to evaluate the response of different soybean cultivars grown under these stressful conditions regarding their susceptibility to GS production and to determine the chlorophyll retention levels and the chlorophyllase activity in the seeds. Seeds of four soybean cultivars [BRS 133, CD 206, MG/BR 46 (Conquista) and BRSMG 251 (Robusta)] were grown under greenhouse conditions until R5.5. At R6, the plants were transferred to phytotrons under temperature stress (from 28ºC to 36ºC) and with water stresses of 10% gravimetric moisture, no water and normal supply. Seeds were harvested at R9 when the percentage of GS and weight of 100 seeds were determined. The contents of a, b and total chlorophylls and the chlorophyllase activity were also determined. The expression of GS production under these conditions varied among cultivars: Conquista and Robusta were considered more susceptible to the production of GS compared to 'BRS 133' and 'CD 206'. These cultivars produced lower GS levels, lower chlorophyll retention and higher chlorophyllase activity compared to Robusta and Conquista. Soybean plants submitted to water and temperature stresses produced high levels of GS, which were small, light and had high chlorophyll contents and low chlorophyllase activity. The contents of a, b and total chlorophylls in GS were inversely proportional to the chlorophyllase activity.

Drift dispersal in central Southern Ontario /

Two tills are readily identi-f i able in central Southern Ontario, a very stony, loose deposit o-f variable matrix (Dummer till) and a moderately stony, fissile and compact deposit that is more homogeneous (drumlinized till). The quantity o-f Precambr i an, Paleozoic and Shadow Lake Formation (Paleozoic) rock types were determined and corresponding isopleth maps drawn. The changes in lithology content occurred in the direction o-f transport, there-fore, compositional isopleths o-f till may be considered equipotential lines for the reconstruction of glacier flow paths. Areal gradations of drift lithology indicated that the prime agents of dispersal were ice and glacial meltwaters. The down-ice abundance trend of till components indicated a dispersal pattern showing the concentration of a given lithology type peaking within a few kilometres of the source followed by a rapid decline and thereafter, a more gradual decrease with increasing distance. Within the esker deposits, igneous rocks may form the major component and can extend further onto the limestone plain than in the adjacent till. Evidence is presented that indicates the "style" of dispersal was one in which glacial ice may have been strongly influenced by local bedrock topography and the regional structural trends. The ice tended to follow pre-existing valleys and lows, depositing till composed mainly of local bedrock. Gradations in Paleozoic clast content showed that the local bedrock lithology became the primary till component within 3 km of down-ice transport. Evidence is presented that indicated the last glaciation may have occurred as a relatively thin ice mass, followed by stagnation and recession. No evidence of a lateglacial re-advance was found within the study area. Because of the lack of a contact between the Dummer and drumlinized till, and because of results showing gradation of the Dummer till into the drumlinized till (as indicated by lithology content and grain size), it is suggested that no re-advance occurred.

Building wood debris piles benefits avian seed dispersers in burned and logged Mediterranean pine forests

Salvage logging is a common practice carried out in burned forests worldwide, and intended to mitigate the economic losses caused by wildfires. Logging implies an additional disturbance occurring shortly after fire, although its ecological effects can be somewhat mitigated by leaving wood debris on site. The composition of the bird community and its capacity to provide ecosystem services such as seed dispersal of fleshy-fruited plants have been shown to be affected by postfire logging. We assessed the effects of the habitat structure resulting from different postfire management practices on the bird community, in three burned pine forests in Catalonia (western Mediterranean). For this purpose, we focused on the group of species that is responsible for seed dispersal, a process which takes place primarily during the winter in the Mediterranean basin. In addition, we assessed microhabitat selection by seed disperser birds in such environments in relation to management practices. Our results showed a significant, positive relationship between the density of wood debris piles and the abundance of seed disperser birds. Furthermore, such piles were the preferred microhabitat of these species. This reveals an important effect of forest management on seed disperser birds, which is likely to affect the dynamics of bird-dependent seed dispersal. Thus, building wood debris piles can be a useful practice for the conservation of both the species and their ecosystem services, while also being compatible with timber harvesting

Efectes de la invasió de la formiga argentina, Linepithema humile (Mayr), sobre el procés de dispersió de llavors de plantes mediterrànies

La formiga invasora Linepithema humile (Mayr), també coneguda com la formiga argentina, és una espècie present a la península Ibèrica. En aquesta tesi s'ha estudiat com afecta la presència d'aquesta espècie plaga a la comunitat de formigues autòctones y al procés de dispersió de llavors de plantes mediterrànies. L'estudi es va dur a terme en una àrea de sureda i brolla d'estepes i bruc boal situada al nord-est peninsular, prop de la línia de costa mediterrània. Un dels primers y més notables efectes de la invasió a les nostres àrees d'estudi és la dramàtica alteració de la comunitat de formigues, en forma de una reducció de la riquesa específica i de la homogeneïtat d'abundàncies. A més, a les zones envaïdes no hi queda cap espècie de formiga autòctona dispersant de llavors. A causa de la gran abundància d'obreres de la formiga argentina a les zones envaïdes, i del seu elevat ritme d'activitat, aquesta espècie efectua un intens rastreig del sòl, la qual cosa li permet localitzar els recursos en un temps menor que les formigues autòctones de les zones no envaïdes. No obstant, la obertura mandibular de la comunitat de formigues esdevé molt disminuïda a les zones envaïdes a causa de la desaparició de les espècies autòctones, la majoria d'elles de mida més grossa que la formiga argentina, la qual cosa podria limitar la capacitat de manipulació de l'entorn que té la comunitat de formigues a les zones envaïdes, i podria explicar la falta de reemplaçament d'alguns dels rols que duien a terme les espècies de formigues autòctones abans de la invasió. La formiga argentina es mostra atreta per les llavors de les nou espècies vegetals estudiades (dues euforbiàcies: Euphorbia biumbellata i E. characias; dues compostes: Cirsium vulgare i Galactites tomentosa; i cinc papilionàcies: Genista linifolia, G. monspessulana, G. triflora, Sarothamnus arboreus i Ulex parviflorus), arribant a transportar i fins i tot introduir al niu algunes llavors, però amb probabilitats inferiors a les realitzades per les formigues autòctones de les zones no envaïdes. No obstant, el seu comportament davant les nou espècies de llavors és variable, de manera que sembla que el seu efecte sobre la dispersió de llavors podria ser diferent per a cada espècie vegetal. L'alteració del procés de dispersió no sembla alterar l'èxit reproductiu d'una espècie concreta, Euphorbia characias, a les zones envaïdes; ni el seu reclutament, ni la distribució espacial, ni la supervivència de les plàntules són significativament diferents a les zones envaïdes que a les no envaïdes. La desaparició de les espècies de formigues granívores de les zones envaïdes pot afectar la dinàmica de les llavors de plantes no mirmecòcores. Així, les llavors de tres papilionàcies (Calicotome spinosa, Psoralea bituminosa i Spartium junceum) resulten amb un menor nivell de transports (i probablement menor depredació) a les zones envaïdes per la formiga argentina.