Restoring Remote Ecosystems

Indirect effects from climate‐driven changes in ecosystems that are remote from direct human activity pose challenges for ecological restoration. Significant and often indirect impacts on alpine ecosystems, the primary ecosystem under consideration in this article, threaten historical‐reference conditions and the viability of some species. The impetus for restoration is similar to projects involving more direct and proximate impacts, but the issues are more complicated in remote ecosystems. Restoration efforts in remote ecosystems might do more harm than good, and the effort required for effective restoration might be greater than easily justified given the shortfall of resources for restoring more heavily impacted ecosystems. The long duration and integration of impacts on remote landscapes pose a distinct set of challenges to restorationists. Intervening in remote ecosystems makes them less remote by definition (they are now affected by human agency). In this article, we examine scientific, technical, and moral issues and offer an initial model for assessing the appropriateness of restoring remote landscapes.     

Temporal change in the diversity-invasibility relationship in the presence of a disturbance regime

Disturbance can affect both the diversity and invasibility of communities. Many field studies have found correlations between diversity and susceptibility to invasion, but if both factors independently respond to disturbance then spurious non-causal relationships may be observed. Here, we show that disturbance can cause a temporal shift in the diversity-invasibility relationship. In a field experiment using sessile marine communities, disturbance strongly affected both diversity and invasion such that they were highly correlated. Disturbance facilitated initial invasion, creating a negative diversity-invasibility relationship when the invader first arrived. Over time, disturbance hindered the persistence of invaders, creating a positive diversity-invasibility relationship. We suggest that temporal changes in the diversity-invasibility relationship may have contributed to the 'invasion paradox', a term for the contrasting patterns of experimental and observational studies of the diversity-invasibility relationship.     

Abundance of introduced species at home predicts abundance away in herbaceous communities

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.     

Genetic parsimony: a factor in the evolution of complexity, order and emergence

Two conjectures, drawn from Gregory Chaitin's Algorithmic Information Theory, are examined with respect to the relationship between an algorithm and its product; in particular his finding that, where an algorithm is minimal, its length provides a measure of the complexity of the product. Algorithmic complexity is considered from the perspective of the relationship between genotype and phenotype, which Chaitin suggests is analogous to other algorithm-product systems. The first conjecture is that the genome is a minimal set of algorithms for the phenotype. Evidence is presented for a factor, here termed 'genetic parsimony', which is thought to have helped minimize the growth of genome size during evolution. Species that depend on rapid replication, such as prokaryotes which are generally r -selected are more likely to have small genomes, while the K -strategists accumulate introns and have large genomes. The second conjecture is that genome size could provide a measure of organism complexity. A surrogate index for coding DNA is in agreement with an established phenotypic index (number of cell types), in exhibiting an evolutionary trend of increasing organism complexity over time. Evidence for genetic parsimony indicates that simplicity in coding has been selected, and is responsible for phenotypic order. It is proposed that order evolved because order in the phenotype can be encoded more economically than disorder. Thus order arises due to selection for genetic parsimony, as does the evolution of other 'emergent' properties.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 295–308.     

The C-value enigma in plants and animals: a review of parallels and an appeal for partnership

• Aims Plants and animals represent the first two kingdomsrecognized, and remain the two best-studied groups in termsof nuclear DNA content variation. Unfortunately, the traditionalchasm between botanists and zoologists has done much to preventan integrated approach to resolving the C-value enigma, thelong-standing puzzle surrounding the evolution of genome size.This grand division is both unnecessary and counterproductive,and the present review aims to illustrate the numerous linksbetween the patterns and processes found in plants and animalsso that a stronger unity can be developed in the future. • Scope This review discusses the numerous parallels thatexist in genome size evolution between plants and animals, including(i) the construction of large databases, (ii) the patterns ofDNA content variation among taxa, (iii) the cytological, morphological,physiological and evolutionary impacts of genome size, (iv)the mechanisms by which genomes change in size, and (v) thedevelopment of new methodologies for estimating DNA contents. • Conclusions The fundamental questions of the C-valueenigma clearly transcend taxonomic boundaries, and increasedcommunication is therefore urged among those who study genomesize evolution, whether in plants, animals or other organisms.     

Microsatellite DNA analysis shows that greater sage grouse leks are not kin groups

The spectacular social courtship displays of lekking birds are thought to evolve via sexual selection, but this view does not easily explain the participation of many males that apparently fail to mate. One of several proposed solutions to this 'lek skew paradox' is that kin selection favours low-ranking males joining leks to increase the fitness of closely related breeders. We investigated the potential for kin selection to operate in leks of the greater sage grouse, Centrocercus urophasianus, by estimating relatedness between lekking males using microsatellite DNA markers. We also calibrated these estimates using data from known families. Mean relatedness within leks was statistically indistinguishable from zero. We also found no evidence for local clustering of kin during lek display, although males tended to range closer to kin when off the lek. These results make kin selection an unlikely solution to the lek skew paradox in sage grouse. Together with other recent studies, they also raise the question of why kin selection apparently promotes social courtship in some lekking species, but not in others.     

SEXUAL CONFLICT AND THE MAINTENANCE OF MULTIVARIATE GENETIC VARIATION

Mate choice should erode additive genetic variation in sexual displays, yet these traits often harbor substantial genetic variation. Nevertheless, recent developments in quantitative genetics have suggested that multivariate genetic variation in the combinations of traits under selection may still be depleted. Accordingly, the erosion and maintenance of variation may only be detectable by studying whole suites of traits. One potential process favoring the maintenance of genetic variance in multiple trait combinations is the modification of sexual selection via sexually antagonistic interactions between males and females. Here we consider how interlocus sexual conflict can shape the genetic architecture of male sexual traits in the cricket, Teleogryllus commodus. In this species, the ability of each sex to manipulate insemination success significantly alters the selection acting on male courtship call properties. Using a quantitative genetic breeding design we estimated the additive genetic variation in these traits and then predicted the change in variation due to previously documented patterns of sexual selection. Our results indicate that female choice should indeed deplete multivariate genetic variance, but that sexual conflict over insemination success may oppose this loss of variance. We suggest that changes in the direction of selection due to sexually antagonistic interactions will be an important and potentially widespread factor in maintaining multivariate genetic variation.     

Species-Rich Scandinavian Grasslands are Inherently Open to Invasion

Invasion of native habitats by alien or generalist species is recognized worldwide as one of the major causes behind species decline and extinction. One mechanism determining community invasibility, i.e. the susceptibility of a community to invasion, which has been supported by recent experimental studies, is species richness and functional diversity acting as barriers to invasion. We used Scandinavian semi-natural grasslands, exceptionally species-rich at small spatial scales, to examine this mechanism, using three grassland generalists and one alien species as experimental invaders. Removal of two putative functional groups, legumes and dominant non-legume forbs, had no effect on invasibility except a marginally insignificant effect of non-legume forb removal. The amount of removed biomass and original plot species richness had no effect on invasibility. Actually, invasibility was high already in the unmanipulated community, leading us to further examine the relationship between invasion and propagule pressure, i.e. the inflow of seeds into the community. Results from an additional experiment suggested that these species-rich grasslands are effectively open to invasion and that diversity may be immigration driven. Thus, species richness is no barrier to invasion. The high species diversity is probably in itself a result of the community being highly invasible, and species have accumulated at small scales during centuries of grassland management.     

Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types

The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species.     

Maintenance and loss of heterozygosity in a thelytokous lineage of honey bees (Apis mellifera capensis)

An asexual lineage that reproduces by automictic thelytokous parthenogenesis has a problem: rapid loss of heterozygosity resulting in effective inbreeding. Thus, the circumstances under which rare asexual lineages thrive provide insights into the trade-offs that shape the evolution of alternative reproductive strategies across taxa. A socially parasitic lineage of the Cape honey bee, Apis mellifera capensis, provides an example of a thelytokous lineage that has endured for over two decades. It has been proposed that cytological adaptations slow the loss of heterozygosity in this lineage. However, we show that heterozygosity at the complementary sex determining (csd) locus is maintained via selection against homozygous diploid males that arise from recombination. Further, because zygosity is correlated across the genome, it appears that selection against diploid males reduces loss of homozygosity at other loci. Selection against homozygotes at csd results in substantial genetic load, so that if a thelytokous lineage is to endure, unusual ecological circumstances must exist in which asexuality permits such a high degree of fecundity that the genetic load can be tolerated. Without these ecological circumstances, sex will triumph over asexuality. In A. m. capensis, these conditions are provided by the parasitic interaction with its conspecific host, Apis mellifera scutellata.