Effects of preservation by ethanol on δ13 C and δ15 N of three tissues of the critically endangered European eel Anguilla anguilla.

The temporal effects of ethanol preservation on the δ13 C and δ15 N values of tissues excised from European eel Anguilla anguilla were assessed. Preservation significantly enriched 13 C values of fin and mucus but not dorsal muscle. The 13 C enrichment occurred in the initial 15 days of preservation and was independent of initial eel mass. Tissue preservation effects on δ15 N values were negligible. These tissue-specific isotopic shifts should be considered when ethanol-preserved eel samples are used.

Contemporary perspectives on the ecological impacts of invasive freshwater fishes.

Introductions of non-native freshwater fish continue to increase globally, although only a small proportion of these introductions will result in an invasion. These invasive populations can cause ecological impacts in the receiving ecosystem through processes including increased competition and predation pressure, genetic introgression and the transmission of non-native pathogens. Definitions of ecological impact emphasize that shifts in the strength of these processes are insufficient for characterizing impact alone and, instead, must be associated with a quantifiable decline of biological and/or genetic diversity and lead to a measurable loss of diversity or change in ecosystem functioning. Assessments of ecological impact should thus consider the multiple processes and effects that potentially occur from invasive fish populations where, for example, impacts of invasive common carp Cyprinus carpio populations are through a combination of bottom-up and top-down processes that, in entirety, cause shifts in lake stable states and decreased species richness and/or abundances in the biotic communities. Such far-reaching ecological impacts also align to contemporary definitions of ecosystem collapse, given they involve substantial and persistent declines in biodiversity and ecosystem functions that cannot be recovered unaided. Thus, while not all introduced freshwater fishes will become invasive, those species that do develop invasive populations can cause substantial ecological impacts, where some of the impacts on biodiversity and ecosystem functioning might be sufficiently harmful to be considered as contributing to ecosystem collapse.

Native drivers of fish life history traits are lost during the invasion process.

Rapid adaptation to global change can counter vulnerability of species to population declines and extinction. Theoretically, under such circumstances both genetic variation and phenotypic plasticity can maintain population fitness, but empirical support for this is currently limited. Here, we aim to characterize the role of environmental and genetic diversity, and their prior evolutionary history (via haplogroup profiles) in shaping patterns of life history traits during biological invasion. Data were derived from both genetic and life history traits including a morphological analysis of 29 native and invasive populations of topmouth gudgeon Pseudorasbora parva coupled with climatic variables from each location. General additive models were constructed to explain distribution of somatic growth rate (SGR) data across native and invasive ranges, with model selection performed using Akaike's information criteria. Genetic and environmental drivers that structured the life history of populations in their native range were less influential in their invasive populations. For some vertebrates at least, fitness-related trait shifts do not seem to be dependent on the level of genetic diversity or haplogroup makeup of the initial introduced propagule, nor of the availability of local environmental conditions being similar to those experienced in their native range. As long as local conditions are not beyond the species physiological threshold, its local establishment and invasive potential are likely to be determined by local drivers, such as density-dependent effects linked to resource availability or to local biotic resistance.

Phenotypic responses of invasive species to removals affect ecosystem functioning and restoration.

Reducing the abundances of invasive species by removals aims to minimize their ecological impacts and enable ecosystem recovery. Removal methods are usually selective, modifying phenotypic traits in the managed populations. However, there is little empirical evidence of how removal-driven changes in multiple phenotypic traits of surviving individuals of invasive species can affect ecosystem functioning and recovery. Overcoming this knowledge gap is highly relevant because individuals are the elemental units of ecological processes and so integrating individual-level responses into the management of biological invasions could improve their efficiency. Here we provide novel demonstration that removals by trapping, angling and biocontrol from lakes of the globally invasive crayfish Procambarus clarkii induced substantial changes in multiple phenotypic traits. A mesocosm experiment then revealed that these changes in phenotypic traits constrain recovery of basic ecosystem functions (decomposition of organic matter, benthic primary production) by acting in the opposite direction than the effects of reduced invader abundance. However, only minor ecological impacts of invader abundance and phenotypic traits variation remained a year after its complete eradication. Our study provides quantitative evidence to an original idea that removal-driven trait changes can dampen recovery of invaded ecosystems even when the abundance of invasive species is substantially reduced. We suggest that the phenotypic responses of invaders to the removal programme have strong effects on ecosystem recovery and should be considered within the management of biological invasions, particularly when complete eradication is not achievable.

How many founders for a biological invasion? Predicting introduction outcomes from propagule pressure.

Ecological theory on biological invasions attempts to characterize the predictors of invasion success and the relative importance of the different drivers of population establishment. An outstanding question is how propagule pressure determines the probability of population establishment, where propagule pressure is the number of individuals of a species introduced into a specific location (propagule size) and their frequency of introduction (propagule number). Here, we used large-scale replicated mesocosm ponds over three reproductive seasons to identify how propagule size and number predict the probability of establishment of one of world's most invasive fish, Pseudorasbora parva, as well as its effect on the somatic growth of individuals during establishment. We demonstrated that, although a threshold of 11 introduced pairs of fish (a pair is 1 male, 1 female) was required for establishment probability to exceed 95%, establishment also occurred at low propagule size (1-5 pairs). Although single introduction events were as effective as multiple events at enabling establishment, the propagule sizes used in the multiple introductions were above the detected threshold for establishment. After three reproductive seasons, population abundance was also a function of propagule size, with rapid increases in abundance only apparent when propagule size exceeded 25 pairs. This was initially assisted by adapted biological traits, including rapid individual somatic growth that helped to overcome demographic bottlenecks.

Management implications of the response of two tilapiine cichlids to long-term changes in lake level, allodiversity and exploitation in an equatorial lake.

The tilapiine cichlids Oreochromis leucostictus and Tilapia zillii were introduced into Lake Naivasha, Kenya, in 1956. Previous studies on data collected to 1987 revealed they were persistent following establishment, despite environmental variability and exploitation. Recent data, however, suggest this persistence is under threat as data indicate some significant declines in aspects of their abundance since 1999. The influence of changes in lake level, allodiversity and fishing effort on this decline was tested and showed that a decline in lake level was a significant causal factor. The recent change in allodiversity, with the establishment and dominance of Cyprinus carpio in the fishery, was not significant on the catch per unit effort of O. leucostictus but was on T. zillii. Since 1999, catches of tilapiines in the fishery have been independent of fishing effort, contrary to between 1975 and 1987, suggesting their management through application of fishery models may no longer be applicable. As it was anthropogenic-mediated lake level changes that were mainly responsible for their decline, then lake management should focus on sustainable water utilization that maximizes lake levels in accordance with the basin-wide water balance.