Population genetic diversity influences colonization success

Much thought has been given to the individual‐level traits that may make a species a successful colonizer. However, these traits have proven to be weak predictors of colonization success. Here, we test whether population‐level characteristics, specifically genetic diversity and population density, can influence colonization ability on a short‐term ecological timescale, independent of longer‐term effects on adaptive potential. Within experimentally manipulated populations of the weedy herb Arabidopsis thaliana, we found that increased genetic diversity increased colonization success measured as population‐level seedling emergence rates, biomass production, flowering duration, and reproduction. Additive and non‐additive effects contributed to these responses, suggesting that both individual genotypes (sampling effect) and positive interactions among genotypes (complementarity) contributed to increased colonization success. In contrast, manipulation of plant density had no effect on colonization success. The heightened ability of relatively genetically rich populations to colonize novel habitats, if a general phenomenon, may have important implications for predicting and controlling biological invasions.     

The role of preadaptation,propagule pressure and competition in the colonization of new habitats

To successfully colonize new habitats, organisms not only need to gain access to it, they also need to cope with the selective pressures imposed by the local biotic and abiotic conditions. The number of immigrants, the preadaptation to the local habitat and the presence of competitors are important factors determining the success of colonization. Here, using two experimental set-ups, we studied the effect of interspecific competition in combination with propagule pressure and preadaptation on the colonization success of new habitats. Our model system consisted of tomato plants (the novel habitat), the two-spotted spider mite Tetranychus urticae as our focal species and the red spider mite Tetranychus evansi as a competitor. Our results show that propagule pressure and preadaptation positively affect colonization success. More successful populations reach larger final population sizes either by having higher per capita growth rates (due to preadaptation effects) or by starting a population with a larger number of individuals. Although populations are more successful colonizing non-competitive environments than competitive ones, propagule pressure and preadaptation counteract the negative effects of competition, promoting colonization success. Our study shows the importance of propagule pressure and preadaptation for successful colonization of new habitats by providing the ability to cope with both the exigencies of new environments and the community context.     

Population‐level traits that affect,and do not affect,invasion success

What allows some species to successfully colonize a novel environment while others fail? Numerous studies in invasion biology have sought to answer this question, but those studies have tended to focus on traits of species or individuals (e.g. body size, seed size, seed number), and these traits have largely been found to be weak predictors of invasion success. However, characteristics of colonizing populations (e.g. genetic diversity, density, age structure) might also be important for successful establishment, as the authors of a study published in this issue of Molecular Ecology show ( Crawford & Whitney 2010 ). By experimentally manipulating the density and genetic diversity of colonizing populations of Arabidopsis thaliana, the authors found that genetic diversity, but not population density, increased colonization success. Importantly, the effects of genetic diversity on colonization success were both additive and non‐additive, suggesting that traits associated with particular genotypes and complimentarity among genotypes contribute to colonization success. This research highlights the importance of considering within‐species variation and characteristics of entire populations in predicting colonization success.     

Sugarbeet culture and mormon economic development in the Intermountain West

Beta vulgaris L. played an important economic role in Mormon settlements from 1852 to 1979. The introduction of the sugarbeet from Europe supplied not only a source of sugar and income, but also a sense of dignity and independence to early Mormon pioneers seeking refuge from intense religious persecution. As the major cash crop in early Mormon settlements, cultivation of sugarbeet directly provided security for farmers, and indirectly the economic foundation for workers in many other areas. However, in the last three decades, changes in world and U.S. sugar prices have rendered sugarbeet cultivation in some areas of the Intermountain West economically untenable, and the crop has been commercially abandoned.     

Neutral and adaptive drivers of genomic change in introduced brook trout (Salvelinus fontinalis) populations revealed by pooled sequencing

Understanding the drivers of successful species invasions is important for conserving native biodiversity and for mitigating the economic impacts of introduced species. However, whole‐genome resolution investigations of the underlying contributions of neutral and adaptive genetic variation in successful introductions are rare. Increased propagule pressure should result in greater neutral genetic variation, while environmental differences should elicit selective pressures on introduced populations, leading to adaptive differentiation. We investigated neutral and adaptive variation among nine introduced brook trout (Salvelinus fontinalis) populations using whole‐genome pooled sequencing. The populations inhabit isolated alpine lakes in western Canada and descend from a common source, with an average of ~19 (range of 7–41) generations since introduction. We found some evidence of bottlenecks without recovery, no strong evidence of purifying selection, and little support that varying propagule pressure or differences in local environments shaped observed neutral genetic variation differences. Putative adaptive loci analysis revealed nonconvergent patterns of adaptive differentiation among lakes with minimal putatively adaptive loci (0.001%–0.15%) that did not correspond with tested environmental variables. Our results suggest that (i) introduction success is not always strongly influenced by genetic load; (ii) observed differentiation among introduced populations can be idiosyncratic, population‐specific, or stochastic; and (iii) conservatively, in some introduced species, colonization barriers may be overcome by support through one aspect of propagule pressure or benign environmental conditions.     

Roads,speculators, and colonization in the Ecuadorian Amazon

In view of the generally disappointing performance of colonization projects in the Amazon basin, unusual projects merit close scrutiny because they may suggest a more effective organizational form for the colonization of humid lowlands. With this end in mind, this article examines those aspects of the Upano-Palora project in southeastern Ecuador that are attributable to the project's unusual plan of establishing settlements first and building the roads afterwards. It concludes that the “settlements first, roads second” developmental sequence reduced the costs of the project, produced an egalitarian pattern of landownership, and contributed to a pattern of land use that had potentially damaging ecological effects. These findings suggest that variations in the timing of road building have an important impact on outcomes in new land settlement schemes.     

Habitat use by Nonnative Rainbow Trout, Oncorhynchus mykiss, and Native Little Colorado spinedace, Lepidomeda vittata

We evaluated overlap in microhabitat use between nonnative rainbow trout, Oncorhynchus mykiss, and native Little Colorado spinedace, Lepidomeda vittata, a federally threatened cyprinid, in natural and experimental settings. In natural settings, we also examined occurrence and microhabitat use of two other native fishes, speckled dace, Rhinichthys osculus, and bluehead sucker, Catostomus discobolus. Native species co-occurred, as did rainbow trout and bluehead sucker. However, occurrences of Little Colorado spinedace and speckled dace were not significantly correlated with occurrence of rainbow trout. Total lengths of all three native species were significantly smaller at allopatric sites than at sites sympatric with rainbow trout. Microhabitat characteristics at sites with rainbow trout did not differ from those where the other three species were found, but did differ among the native species. In laboratory experiments with Little Colorado spinedace and rainbow trout, rainbow trout used the lower depth zone most, and spinedace increased use of the lower depth zone upon addition of rainbow trout. In addition, species tended to co-occur in zones, but used cover independently of one-another, suggesting a low level of agonistic interactions. However, after addition of a high density of rainbow trout, spinedace tended to use cover less than before. We suggest that the species can coexist at low rainbow trout densities. Potential negative effects of rainbow trout on Little Colorado spinedace likely increase with increasing densities of rainbow trout, and rainbow trout likely affect smaller size classes of Little Colorado spinedace more than larger ones.     

Fine-scale genetic structure, estuarine colonization and incipient speciation in the marine silverside fish Odontesthes argentinensis

The identification of incipient ecological species represents an opportunity to investigate current evolutionary process where adaptive divergence and reproductive isolation are associated. In this study we analysed the genetic structure of marine and estuarine populations of the silverside fish Odontesthes argentinensis using nine microsatellite loci and 396 bp of the mitochondrial DNA (mtDNA) control region. Our main objective was to investigate the relationship among estuarine colonization, divergent selection and speciation in silversides. Significant genetic structure was detected among all marine and estuarine populations. Despite the low phylogeographic structure in mtDNA haplotypes, there was clear signal of local radiations of haplotypes in more ancient populations. Divergence among marine populations was interpreted as a combined result of homing behaviour, isolation by distance and drift. On the other hand, ecological shifts due to the colonization of estuarine habitats seem to have promoted rapid adaptive divergence and reproductive isolation in estuarine populations, which were considered as incipient ecological species. This conclusion is supported by the existence of a set of environmental factors required for successful reproduction of estuarine ecotypes. The pattern of genetic structure indicates that phenotypic and reproductive divergence evolved in the face of potential gene flow between populations. We suggest that the 'divergence-with-gene-flow' model of speciation may account for the diversification of estuarine populations. The approach used can potentially identify 'incipient estuarine species', being relevant to the investigation of the evolutionary relationships of silversides in several coastal regions of the world.     

Radiotelemetry reveals differences in individual movement patterns between outbreak and non-outbreak Mormon cricket populations

Abstract.  1. Outbreaks of insect pest populations are common and can have devastating effects on natural communities and on agriculture. Little is known about the causes of these outbreaks or the causes of en masse migrations during outbreaks.
2. Flightless Mormon crickets ( Anabrus simplex ) were the focus of this study. They are a katydid species that forms large, dense, mobile groups (migratory bands) during outbreak periods, eating vegetation in their path.
3. Radiotelemetric methods were used to measure differences in movement rate and directionality in outbreak and non-outbreak populations, testing the hypothesis that these populations differ in their travel rate and consistency of direction.
4. Daily individual movement in outbreak populations differs substantially from non-outbreak populations that are at much lower density. In addition to large differences in distances travelled (1.6 km as compared with 1 m) and rates of travel, there is evidence for collective movement among individual Mormon crickets travelling in migratory bands.
5. These data suggest that the direction of group movement may be influenced by local environmental conditions such as wind direction and movement of nearby band members. This work forms the basis for ongoing work testing hypotheses about mass migrations in outbreak populations.     

How Do Real Indians Fish? Neoliberal Multiculturalism and Contested Indigeneities in the Colorado Delta

ABSTRACT   There has been a growing interest in anthropology regarding how certain political conditions set the stage for "articulations" between indigenous movements and environmental actors and discourses. However, relatively little attention has been paid to how these same conditions can suppress demands for indigenous rights. In this article, I argue that the pairing of neoliberalism and multiculturalism in contemporary Mexico has created political fields in which ethnic difference has been foregrounded as a way of denying certain rights to marginalized groups. Drawing on ethnographic fieldwork conducted in northern Mexico, I analyze how the arguments of a group of Cucapá for fishing rights in the Colorado Delta have been constrained within these political circumstances. I argue that cultural difference has been leveraged by the Mexican federal government and local NGOs to prevent the redistribution of environmental resources among vulnerable groups such as the Cucapá.     

A quantitative life history of endangered humpback chub that spawn in the Little Colorado River: variation in movement,growth, and survival

While the ecology and evolution of partial migratory systems (defined broadly to include skip spawning) have been well studied, we are only beginning to understand how partial migratory populations are responding to ongoing environmental change. Environmental change can lead to differences in the fitness of residents and migrants, which could eventually lead to changes in the frequency of the strategies in the overall population. Here, we address questions concerning the life history of the endangered Gila cypha (humpback chub) in the regulated Colorado River and the unregulated tributary and primary spawning area, the Little Colorado River. We develop eight multistate models for the population based on three movement hypotheses, in which states are defined in terms of fish size classes and river locations. We fit these models to mark–recapture data collected in 2009–2012. We compare survival and growth estimates between the Colorado River and Little Colorado River and calculate abundances for all size classes. The best model supports the hypotheses that larger adults spawn more frequently than smaller adults, that there are residents in the spawning grounds, and that juveniles move out of the Little Colorado River in large numbers during the monsoon season (July–September). Monthly survival rates for G. cypha in the Colorado River are higher than in the Little Colorado River in all size classes; however, growth is slower. While the hypothetical life histories of life‐long residents in the Little Colorado River and partial migrants spending most of its time in the Colorado River are very different, they lead to roughly similar fitness expectations when we used expected number of spawns as a proxy. However, more research is needed because our study period covers a period of years when conditions in the Colorado River for G. cypha are likely to have been better than has been typical over the last few decades.     

Disrupting spring colonization of Colorado potato beetle to nonrotated potato fields

Overwintering Colorado potato beetles (Leptinotarsa decemlineata (Say)) were concentrated primarily within woody borders, and mortality was lower in borders than in potato fields. After overwintering, only 15–44% of live beetles were in the potato fields. In experiments with small plots, colonization of fields from woody borders was reduced ∼60% by a trap crop, either treated with adulticide or with beetles collected daily. Such trap crops, or simply pitfall traps to prevent colonization from woody borders, could significantly reduce early-season adult numbers and subsequent larval populations. However, success is dependent on the local densities of overwintered beetles, and the prevalence of arrestment behavior in the case of trap crops.     

Community monopolization: local adaptation enhances priority effects in an evolving metacommunity

The diversity and composition of biological communities might often depend on colonization history because early colonists can exclude future colonists through a priority effect. These priority effects, which have been observed across a wide variety of ecosystems, often arise because early colonists have sufficient time to use available resources efficiently and subsequently withhold them from invaders. Here, we explore the extent to which rapid local adaptive evolution contributes to the pervasiveness of these priority effects. Using an individual-based simulation, we show that early colonization allows the descendants of colonists to adapt to novel conditions and reduce the establishment success of an initially ecologically equivalent competing species. Our model predicts that slight differences in colonization timing and adaptive capacity between species can substantially alter the dynamics and diversity of communities. We also show that priority effects and gene flow can generate a novel mechanism for the expansion and retraction of species distributions in a metacommunity. Our results suggest that local adaptation combined with stochastic colonization events can obscure direct relationships between species distributions and environmental gradients. Given the increasing recognition of rapid, microgeographic evolution in natural populations, we expect that evolutionary priority effects could affect the structure and dynamics of many natural metacommunities.     

The social and ecological consequences of early cattle ranching in the Little Colorado River Basin

Commercial cattle ranching began in east central Arizona during the late 1880s when thousands of head of cattle were introduced onto the previously unexploited grasslands of the Little Colorado River Basin. Most of these animals were imported from western Texas where serious overgrazing had resulted in both catastrophic cattle losses and widespread range deterioration. By the turn of the century, the Texas experience had been repeated in Arizona, because Texas cattlemen continued to follow the same destructive stocking practices in this new region. This paper examines: (1) the early development of cattle ranching in the Little Colorado River Basin; (2) the various factors which contributed to overgrazing in the region; and (3) the consequences that commercial cattle ranching had on the local environment and on the pre-existing farming communities of the region.     

Research in Turbulent Environments: Slums in Chennai,India and the Impact of the December 2004 Tsunami on an Ecohealth Project

On December 26, 2004, a tsunami struck coastal areas in the Bay of Bengal. Among the communities affected were Pallavan Nagar and Anju Kudasai slums in Chennai India. These communities have been collaborating, with some success, on a project to manage the urban environment for human health that employs an adaptive ecosystem approach framework, and is heavily influenced by participatory action research methodology. The tsunami resulted in loss of life, shelter, property and livelihoods in these communities. This profile presents an overview of the project, the two settlements, and the impact of the tsunami on the communities. This article also discusses the impact of the disaster on the direction and nature of the ecohealth project.     

Growth and Arbuscular Mycorrhizal Fungal Colonization of Two Prairie Grasses Grown in Soil from Restorations of Three Ages

I compared growth and arbuscular mycorrhizal fungal (AMF) colonization of two prairie grasses (Wild rye [Elymus canadensis] and Little bluestem [Schizachyrium scoparium]), an early‐ and a late‐dominating species in prairie restorations, respectively, grown in soil from restored prairies of differing age, soil characteristics, and site history. There were no consistent patterns between restoration age and soil inorganic nutrients or organic matter. The oldest restoration site had higher soil mycorrhizal inoculum potential (MIP) than 2‐ and 12‐year‐old restorations. However, MIP did not translate into actual colonization for two species grown in soils from the three restorations, nor did MIP relate to phosphorus availability. There were significant differences in root mass and colonization among Wild rye plants but not among Little bluestem plants grown in soils from the three restorations. Wild rye grown in 2‐year‐old restoration soil had significantly higher AMF colonization than when it was grown in soils from the 12‐ and 17‐year‐old restorations. Wild rye grown in 2‐year‐old restoration soil also had higher colonization than Little bluestem grown in 2‐ and 12‐year‐old restoration soils. Little bluestem had no significant correlations between shoot biomass, root biomass or colonization, and concentrations of soil P, total N, or N:P. However, for Wild rye, total soil N was positively correlated with root mass and negatively correlated with colonization, suggesting that in this species, mycorrhizae may affect N availability. Collectively, these results suggest that soil properties unrelated to restoration age were important in determining differences in growth and AMF colonization of two species of prairie grasses.     

Life-history variation and adaptation in the historically mobile plant Arabidopsis thaliana (Brassicaceae) in North America

We used field-collected seeds of Arabidopsis thaliana (Brassicaceae) to simulate a colonization event of plants from diverse locations into a common environment to compare regionally "local" and "foreign" populations of this historically mobile species. Life history varied among regional groups, but most variation was found among populations within regions. While we found significant differences among populations and regional groups for important life-history characters, we did not find significant differences in performance of plants from different populations or regional groups. Rather, we found evidence that differences in life history contributed to the ability of plants from foreign regions to perform comparably to local Kentucky plants. Had plants from different regions not differed in the timing and size of reproduction, we would have seen that Kentucky (local) plants had higher total fitness via greater reproductive success of individuals that survived to reproduce and that Michigan plants would have had the lowest fitness. The populations are comparably adapted to the environment in Kentucky but through different combinations of life-history characters. Therefore, the life-history variation in this mobile species appears to contribute not to fitness differences among populations but rather to success in colonizing new locations.     

Colonization,abundance, and geographic range size of gravestone lichens

Macroecological studies often find that species with large geographic range sizes are also locally abundant. Superior colonization ability of species with large ranges is a possible/plausible explanation for this pattern, yet direct measures of colonization ability are difficult, and thus the relationship between colonization ability and range size is rarely investigated directly. Using a data set of gravestone lichens spanning more than 300 years, we investigated relationships among colonization ability, abundance, and geographic range size. Pairwise correlations were used to compare colonization ability and local abundance with area of occupancy (a measure of range size) and spore size within England, Scotland, and Wales on two different types of gravestones. Indices of colonization ability and abundance were positively correlated with area of occupancy. Colonization ability was significantly positively correlated with local abundance, but it was not at all related to propagule size. When lichen species were grouped categorically by colonization ability, the strongest area-occupancy relationships were observed within the subset of species that were the best colonizers. Significant differences among genera were found in spore size but not for other variables. Lichen species that occupy the largest geographic area were the best colonizers: they were the first species present on newly erected stones. These results complement the more commonly observed macroecological pattern that widespread species are also locally abundant.     

Quantitative genetic approach for assessing invasiveness: geographic and genetic variation in life-history traits

Predicting the spread of invasive species is a challenge for modern ecology. Although many invasive species undergo genetic bottlenecks during introduction to new areas resulting in a loss of genetic diversity, successful invaders manage to flourish in novel environments either because of pre-adaptations or because important traits contain adaptive variation enabling rapid adaptation to changing conditions. To predict and understand invasion success, it is crucial to analyse these features. We assessed the potential of a well-known invader, the Colorado potato beetle (Leptinotarsa decemlineata), to expand north of its current range in Europe. A short growing season and harsh overwintering conditions are apparent limiting factors for this species’ range. By rearing full-sib families from four geographically distinct populations (Russia, Estonia, Poland, Italy) at two fluctuating temperature regimes, we investigated (a) possible differences in survival, development time, and body size among populations and (b) the amount of adaptive variation within populations in these traits. All populations were able to complete their development in cooler conditions than in their current range. A significant genotype–environment interaction for development time and body size suggests the presence of adaptive genetic variation, indicating potential to adapt to cooler conditions. The northernmost population had the highest survival rates and fastest development times on both temperature regimes, suggesting pre-adaptation to cooler temperatures. Other populations had minor differences in development times. Interestingly, this species lacks the classical trade-off between body size and development time which could have contributed to its invasion potential. This study demonstrates the importance of considering both ecological and evolutionary aspects when assessing invasion risk.