Colonization in an abandoned East-Mediterranean vineyard

Abstract. Previous studies on secondary succession in abandoned agricultural land in the Mediterranean area were carried out by the chronosequence method, including data from different sites. A unique opportunity to study secondary succession arose from a situation in which different parts of one homogeneous East-Mediterranean vineyard were abandoned for 5, 8, 15 and 35 yr, and did not suffer from any disturbance subsequently. Most of the perennial species that colonized the abandoned vineyard were fleshy fruited species, which apparently were dispersed by birds from the surrounding maquis into the vineyard. These bird-dispersed species were the first to be established, and were the dominant plant group according to dispersal modes. The abandoned vine plants and their supporting columns provided the birds with perching and feeding sites, enhancing the arrival of bird-dispersed species regardless of their life forms. Under these conditions the most important attribute that affected vegetation dynamics was seed dispersal mode. Trees were among the first to colonize in the vineyard, implying that no facilitation was needed for their establishment. Annual plant species were the only species to disappear during succession. Almost all perennial species which had arrived persisted in the vineyard, and no replacement of perennial species was found. The rate of succession was rapid, as expressed by the short time (8–15 yr) needed for the stabilization of species composition, for growth to average height of late succession trees, and for reaching high cover of the invading perennial species in the abandoned vineyard. The secondary succession described above differs from that in the western Mediterranean by the absence of perennial species replacement and its rapid rate. The possible causes are discussed.     

Biodiversity of soil biota and plants in abandoned arable fields and grasslands under restoration management

The currently widespread abandoning of agricultural land use in Western Europe offers new opportunities for ecological restoration and nature conservation. This is illustrated for abandoned arable fields and for permanent grasslands cut for hay after the cessation of fertilizer application. Although initiated by a sudden reduction of nutrient input to the system, the changing nutrient supply from the soil is considered to be the main driving force of succession. The soil nutrient supply is affected by soil organisms, both directly (root symbionts and herbivores) and indirectly (nutrient mineralization from dead organic matter). It is argued that because of the close association of changes in species diversity with changes in the functioning of ecosystems, biodiversity has to be studied in an ecosystem ecology context.     

Frequency of local, regional, and long-distance dispersal of diploid and tetraploid Saxifraga oppositifolia (Saxifragaceae) to Arctic glacier forelands

? Premise of the Study: Climate change forces many species to migrate. Empirical small-scale data on migration and colonization in the Arctic are scarce. Retreating glaciers provide new territory for cold-adapted plant species, but the genetic consequences depend on dispersal distances and frequencies. We estimated local, regional, and long-distance dispersal frequencies, as well as their effect on levels of genetic diversity, in diploid and tetraploid individuals of Saxifraga oppositifolia. ? Methods: Samples were collected in four aged moraines in each of three glacier forelands, in surrounding areas and reference populations in the Arctic archipelago Svalbard. These samples were analyzed for neutral amplified fragment length polymorphisms (AFLPs, n = 707) and ploidy levels (n = 30). ? Key Results: Genetic clustering and ploidy analyses revealed two distinct genetic groups representing diploids and tetraploids, with few intermediate triploids. The groups were intermixed in most sampled populations. No differences in genetic diversity were found between tetraploids and diploids, or between established and glacier foreland populations. Seeds were dispersed over local, regional, and long distances, with the highest proportions of seeds originating from close sources. A minimum of 4-15 founding individuals from several source populations had initially established in each glacier foreland. ? Conclusions: Our data suggest that S. oppositifolia can rapidly colonize new deglaciated areas without losing genetic diversity. Thus, glacier forelands can be alternative habitats for cold-adapted vascular plants tracking their climatic niche. Our data show no difference in colonization success between diploid and tetraploid individuals.     

Reinvasion of a Riparian Forest Community by an Animal-dispersed Tree Weed Following Control Measures

Patterns of seed dispersal and the effects of mulching upon Celtis sinensis Pers. seedling establishment were investigated following the removal of this tree weed from a riparian forest community. At the commencement of the study there was virtually no representation of C. sinensis in the soil seed bank. However, subsequent rates of seed immigration were high since mature individuals of C. sinensis remained on the boundary of the site. Fruit bats (Pteropus spp.) were the principal dispersal vectors. Seed rain density of C. sinensis was best fitted by an inverse power distribution, with seed densities in excess of 20 m⁻² detected at 70 m from the seed source. Extrapolation from this relationship suggested that a site would have to be more than 350 m from a seed source to reduce the C. sinensis seed rain to less than 1 m⁻². More than 98% of the seed rain occurred below the canopies of the native tree species that remained following the removal of C. sinensis. For these trees, subarboreal C. sinensis seed distributions were not homogeneous, with peak seed densities occurring at different distances from tree trunks in each of the two years that seed distributions were assessed. Mulching with compacted sugar cane trash, corresponding to litter loadings of 6–12 kg m⁻², was imposed early in the study, some weeks before the C. sinensis seed rain commenced. These treatments had no measurable effect upon C. sinensis germination, but substantially reduced seedling survival and had variable effects upon the early growth of seedlings. The potential roles of seed limitation vs establishment limitation are discussed in relation to the management of animal-dispersed invasive species. It is argued that an understanding of the likely levels and patterns of invasion is essential for the formulation of management strategies that can effectively reduce the invasion and impacts of these plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isolation by resistance across a complex coral reef seascape

A detailed understanding of the genetic structure of populations and an accurate interpretation of processes driving contemporary patterns of gene flow are fundamental to successful spatial conservation management. The field of seascape genetics seeks to incorporate environmental variables and processes into analyses of population genetic data to improve our understanding of forces driving genetic divergence in the marine environment. Information about barriers to gene flow (such as ocean currents) is used to define a resistance surface to predict the spatial genetic structure of populations and explain deviations from the widely applied isolation-by-distance model. The majority of seascape approaches to date have been applied to linear coastal systems or at large spatial scales (more than 250 km), with very few applied to complex systems at regional spatial scales (less than 100 km). Here, we apply a seascape genetics approach to a peripheral population of the broadcast-spawning coral Acropora spicifera across the Houtman Abrolhos Islands, a high-latitude complex coral reef system off the central coast of Western Australia. We coupled population genetic data from a panel of microsatellite DNA markers with a biophysical dispersal model to test whether oceanographic processes could explain patterns of genetic divergence. We identified significant variation in allele frequencies over distances of less than 10 km, with significant differentiation occurring between adjacent sites but not between the most geographically distant ones. Recruitment probabilities between sites based on simulated larval dispersal were projected into a measure of resistance to connectivity that was significantly correlated with patterns of genetic divergence, demonstrating that patterns of spatial genetic structure are a function of restrictions to gene flow imposed by oceanographic currents. This study advances our understanding of the role of larval dispersal on the fine-scale genetic structure of coral populations across a complex island system and applies a methodological framework that can be tailored to suit a variety of marine organisms with a range of life-history characteristics.     

Consequences of variable larval dispersal pathways and resulting phenotypic mixtures to the dynamics of marine metapopulations

Larval dispersal can connect distant subpopulations, with important implications for marine population dynamics and persistence, biodiversity conservation and fisheries management. However, different dispersal pathways may affect the final phenotypes, and thus the performance and fitness of individuals that settle into subpopulations. Using otolith microchemical signatures that are indicative of ‘dispersive’ larvae (oceanic signatures) and ‘non-dispersive’ larvae (coastal signatures), we explore the population-level consequences of dispersal-induced variability in phenotypic mixtures for the common triplefin (a small reef fish). We evaluate lipid concentration and otolith microstructure and find that ‘non-dispersive’ larvae (i) have greater and less variable lipid reserves at settlement (and this variability attenuates at a slower rate), (ii) grow faster after settlement, and (iii) experience similar carry-over benefits of lipid reserves on post-settlement growth relative to ‘dispersive’ larvae. We then explore the consequences of phenotypic mixtures in a metapopulation model with two identical subpopulations replenished by variable contributions of ‘dispersive’ and ‘non-dispersive’ larvae and find that the resulting phenotypic mixtures can have profound effects on the size of the metapopulation. We show that, depending upon the patterns of connectivity, phenotypic mixtures can lead to larger metapopulations, suggesting dispersal-induced demographic heterogeneity may facilitate metapopulation persistence.     

Experimental evaluation of sex differences in territory acquisition in a cooperatively breeding bird

In many species, territory ownership is a prerequisite for reproduction;consequently, factors that affect success in territory acquisitioncan have a large impact on fitness. When competing for territories,some individuals may have an advantage if, for example, theyare phenotypically superior or more familiar with the site thanothers. The relative importance of the many factors involvedin territory acquisition is, at present, unclear. We studiedpatterns of natural territory acquisition in a closed and saturatedpopulation of Seychelles warblers. Furthermore, by removingbreeders, we experimentally investigated the relative importance,to territory acquisition, of a range of factors and assessedwhether this differed between the sexes. In both sexes, themain route to natural territory acquisition was to dispersefrom the natal territory to immediately claim a vacant dominantposition. Males were older than females when acquiring a territoryfor the first time. In the removal experiment, for both sexes,the proximity of an individual's natal territory to a vacantdominant position was positively related to the individual'schance of claiming the vacancy. Older males were more likelyto gain an experimental vacant dominant position than were youngmales, whereas age did not affect territory acquisition in females.In the Seychelles warbler, the degree of intrasexual competitionfor territory ownership may be stronger for males than for femalesbecause territory ownership is a prerequisite for male reproduction,whereas females can reproduce on their natal territory. In suchcompetition, young males subsequently lose out to older ones.     

CONFLICTING SELECTION FROM AN ANTAGONIST AND A MUTUALIST ENHANCES PHENOTYPIC VARIATION IN A PLANT

The raw material for evolution is variation. Consequently, identifying the factors that generate, maintain, and erode phenotypic and genetic variation in ecologically important traits within and among populations is important. Although persistent directional or stabilizing selection can deplete variation, spatial variation in conflicting directional selection can enhance variation. Here, we present evidence that phenotypic variation in limber pine (Pinus flexilis) cone structure is enhanced by conflicting selection pressures exerted by its mutualistic seed disperser (Clark's nutcracker Nucifraga columbiana) and an antagonistic seed predator (pine squirrel Tamiasciurus spp.). Phenotypic variation in cone structure was bimodal and about two times greater where both agents of selection co‐occurred than where one (the seed predator) was absent. Within the region where both agents of selection co‐occurred, bimodality in cone structure was pronounced where there appears to be a mosaic of habitats with some persistent habitats supporting only the seed disperser. These results indicate that conflicting selection stemming from spatial variation in community diversity can enhance phenotypic variation in ecologically important traits.