Can increased niche opportunities and release from enemies explain the success of introduced Yellowhammer populations in New Zealand?

Some introduced species succeed spectacularly, becoming far more abundant in their introduced than in their native range. 'Increased niche opportunities' and 'release from enemy regulation' are two hypotheses that have been advanced to explain the enhanced performance of introduced species in their new environments. Using an introduced bird species, the Yellowhammer Emberiza citrinella , which was first released in New Zealand in 1862, as a model, we tested some predictions based on these hypotheses. By quantifying habitat availability and quality, and measuring nest predation rates, we investigated whether increased niche opportunities or release from nest predation could explain the higher density of the Yellowhammer in New Zealand farmland, compared to farmland in their native Britain. Yellowhammer territory densities were over three times higher in New Zealand (0.40 territories per ha) than in comparable British farmland (0.12 territories per ha), and Yellowhammer densities remained significantly higher in New Zealand, after accounting for differences in habitat availability. The density and diversity of invertebrates, a key food resource for nestling Yellowhammers, was significantly lower in New Zealand than in Britain. Hence, these aspects of niche availability and quality cannot explain the higher density of Yellowhammers in New Zealand. Nest predation rates in New Zealand were similar to those in Britain, suggesting that release from nest predation also could not account for the higher density of Yellowhammers in New Zealand. Differences in winter survival, due to differences in winter food supply or the severity of the winter climate, along with release from other types of 'enemy' regulation are possible alternative explanations.     

Are New Zealand's Nothofagus species in equilibrium with their environment?

Abstract. Past explanations of the large disjunctions in the distribution of New Zealand's four Nothofagus species have emphasized displacement during glacial cycles followed by slow re-occupation of suitable sites, or the effects of plate tectonics coupled with ecological and/or environmental limitations to further spread. In this study the degree of equilibrium between Nothofagus distribution and environment was compared with that of other widespread tree species by statistical analysis. Generalized additive regression models were used to relate species distribution data to estimates of temperature, solar radiation, soil water deficit, atmospheric humidity, lithology and drainage. For each species, the amount of spatial patterning remaining unexplained by environment was assessed by adding a variable describing species presence/absence on adjacent plots. Results indicate that Nothofagus species occur more frequently in environments suboptimal for tree growth, i.e. having various combinations of cool temperatures, low winter solar radiation, high root-zone water deficit, low humidity, and infertile granitic substrates. Despite these demonstrated preferences, they exhibit substantially more spatial clustering which is unexplained by environment, than most other widespread tree species. Predictions formed from regressions using environment alone confirm that several major Nothofagus disjunctions are not explicable in terms of the environmental factors used in this analysis, but more likely reflect the effects of historic displacement coupled with slowness to invade forest dominated by more rapidly dispersing endomycorrhizal species. The technique used in this study for detecting residual spatial autocorrelation after fitting explanatory variables has potentially wide application in other studies where either regression or ordination techniques are used for analysis of compositional data.     

Could bacterial associations determine the success of weevil species?

The weevil superfamily Curculionoidea is the largest insect group and so the largest animal group on earth. This taxon includes species which represent an important threat to many economically important crops and, therefore, pose a risk to agriculture and food security. Insect–bacteria associations have been recognised to provide the insect host with many benefits, such as ensuring the acquisition of essential nutrients or protecting the host from natural enemies. The role of bacteria associations within the weevil superfamily remains nonetheless understudied in comparison with other insect taxa. This review draws together existing knowledge on the influence of bacteria associated with weevils known to be agricultural pest species. The implications of these weevil–bacterial associations in determining pest status and their relevance to targeted pest management interventions are discussed. Specific consideration is given to the role of bacteria in cuticle formation, flight activity, reproduction manipulation and adaptation to different environments and food sources.     

Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?

A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously been used to support both hypotheses for the direction of causality. All our predictions are falsified. This study reaffirms that the conventional paradigm in invasion biology is indeed the correct one for New Zealand passerine bird introductions, for which numbers released determine establishment success. Our predictions are not restricted to this fauna, however, and we keenly anticipate their application to other suitable datasets.     

Inside the guts of wood-eating catfishes: can they digest wood?

To better understand the structure and function of the gastrointestinal (GI) tracts of wood-eating catfishes, the gross morphology, length, and microvilli surface area (MVSA) of the intestines of wild-caught Panaque nocturnus, P. cf. nigrolineatus “Marañon”, and Hypostomus pyrineusi were measured, and contrasted against these same metrics of a closely related detritivore, Pterygoplichthys disjunctivus. All four species had anatomically unspecialized intestines with no kinks, valves, or ceca of any kind. The wood-eating catfishes had body size-corrected intestinal lengths that were 35% shorter than the detritivore. The MVSA of all four species decreased distally in the intestine, indicating that nutrient absorption preferentially takes place in the proximal and mid-intestine, consistent with digestive enzyme activity and luminal carbohydrate profiles for these same species. Wild-caught Pt. disjunctivus, and P. nigrolineatus obtained via the aquarium trade, poorly digested wood cellulose (<33% digestibility) in laboratory feeding trials, lost weight when consuming wood, and passed stained wood through their digestive tracts in less than 4 h. Furthermore, no selective retention of small particles was observed in either species in any region of the gut. Collectively, these results corroborate digestive enzyme activity profiles and gastrointestinal fermentation levels in the fishes’ GI tracts, suggesting that the wood-eating catfishes are not true xylivores such as beavers and termites, but rather, are detritivores like so many other fishes from the family Loricariidae.     

Invasions and niche width: does niche width of an introduced crayfish differ from a native crayfish?

1. Human activities have promoted the spread of species worldwide. Several crayfish species have been introduced into new areas, posing a threat to native crayfish and other biota. Invader success may depend on the ability to utilise a wide variety of habitats and resources. Successful invaders are generally expected to have broader niches and to be more plastic than non-invasive species.
2. Using stable isotope ratios of carbon and nitrogen we compared the niche widths of native noble crayfish and introduced signal crayfish, a successful invader of Swedish streams. The calculation of niche width took account of between-site differences in basal resource isotope signature ranges. We also assessed whether population density, prey biomass or prey diversity affected niche width.
3. At the species level, signal crayfish had twice the niche width of noble crayfish. However, individual populations of noble crayfish and signal crayfish in Swedish streams had similar niche widths. This suggests that signal crayfish has greater plasticity with respect to habitat utilisation and feeding than noble crayfish. Niche width in both species correlated positively with benthic invertebrate biomass and diversity, indicating that animal food sources are important for crayfish.
4. We find that assessing niche width in relation to invader success can be a useful tool trying to predict the impact of invasions on different scales. The findings in this study suggest that invaders and natives will have a similar impact on the stream scale whereas the invader will have a larger impact on the regional scale due to the ability to utilise a wider range of streams.     

Challenges of the utilization of wood polymers: how can they be overcome?

Diminishing fossil fuel resources as well as growing environmental and energy security concerns, in parallel with growing demands on raw materials and energy, have intensified global efforts to utilize wood biopolymers as a renewable resource to produce biofuels and biomaterials. Wood is one of the most abundant biopolymer composites on earth that can be converted into biofuels as well as used as a platform to produce bio-based materials. The major biopolymers in wood are cellulose, hemicelluloses, and lignin which account for >90% of dry weight. These polymers are generally associated with each other in wood cell walls resulting in an intricate and dynamic cell wall structure. This mini-review provides an overview of major wood biopolymers, their structure, and recent developments in their utilization to develop biofuels. Advances in genetic modifications to overcome the recalcitrance of woody biomass for biofuels are discussed and point to a promising future.     

Can a breakdown in competition–colonization tradeoffs help explain the success of exotic species in the California flora?

Determining combinations of functional traits that allow a species to colonize new habitats has been central in the development of invasion ecology. Species able to establish in new communities harbor abilities or traits that allow them to use resources or tolerate stress in ways that native species cannot. Tradeoffs among species functional traits along the competition–colonization (CC) continuum, where competitive ability is a decreasing function of dispersal capacity, may allow invasive species to establish themselves in new habitats. The California flora offers a well‐characterized model system to examine whether native and exotic species differ in the distribution of functional traits and to examine whether a breakdown of the CC tradeoff is present. We used a random subset of 1000 plants and examined seed traits and life form characteristics along with their seed size and adult height using the Jepson Manual of the plants of California. To test the hypothesis that active dispersal strategies aid in the success of exotic species, we classified species into four seed types according to the presence/absence of mechanisms associated with efficient dispersal. In addition, for each species we compiled data on seed size and adult plant height. We conducted all comparisons between native and exotic species within the four most speciose families to control for potential taxonomic non‐independence. Exotic species had smaller seed size but greater plant height than natives of the same families. On the other hand, exotic species also displayed significantly greater proportions of functional traits that enhanced dispersal ability. Additionally, certain sets of functional traits were significantly associated with exotic species, such as annual life histories with small seeds and high dispersal capacity. In the random subset of the California flora examined, exotics of the most speciose plant families show functional trait combinations that appear to violate the tradeoff structures observed in their California counterparts. Our results suggest that taxonomically controlled comparisons of the CC tradeoff structure between natives and exotic species may shed light of the capacity of those exotic species invasive ability to colonize new habitats.     

Are there body size implications for the success of globally introduced land birds?

Verbal models have hypothesized a relation between body size and the successful introduction of animal species. This relation is largely based on studies of intrinsic rate of increase in what have been termed "colonizing" species. From these studies it has been predicted that introduction success should be negatively correlated with body size across taxa but positively correlated within closely related taxa. T examine this relation for globally introduced land birds. Introduced land birds are. on average, larger bodied than extant land bird species. Across species, families, and higher family nodes, global introduction success is significantly related to decreasing body size. However, within taxa there is a significant positive relationship between introduction success and body size. I discuss possible explanations for the observed relations and conclude that an indirect but genuine relationship between the introduction success of land birds and their body size is currently the most plausible.     

Can the enemy release hypothesis explain the success of invasive alien predators and parasitoids?

Biological invasions are ecologically and economically costly. Understanding the major mechanisms that contribute to an alien species becoming invasive is seen as essential for limiting the effects of invasive alien species. However, there are a number of fundamental questions that need addressing such as why some communities are more vulnerable to invasion than others and, indeed, why some alien species become widespread and abundant. The enemy release hypothesis (ERH) is widely evoked to explain the establishment and proliferation of an alien species. ERH predicts that an alien species introduced to a new region should experience a decrease in regulation by natural enemies which will lead to an increase in the distribution and abundance of the alien species. At the centre of this theory is the assumption that natural enemies are important regulators of populations. Additionally, the theory implies that such natural enemies have a stronger regulatory effect on native species than they do on alien species in the introduced range, and this disparity in enemy regulation results in increased population growth of the alien species. However, empirical evidence for the role of the ERH in invasion success is lacking, particularly for invertebrates. Many studies equate a reduction in the number of natural enemies associated with an alien species to release without studying population effects. Further insight is required in relation to the effects of specific natural enemies on alien and native species (particularly their ability to regulate populations). We review the role of ecological models in exploring ERH. We suggest that recent developments in molecular technologies offer considerable promise for investigating ERH in a community context.     

Life-history traits of introduced Iberian pumpkinseed Lepomis gibbosus relative to native populations. Can differences explain colonization success?

To assess the colonization success of pumpkinseed Lepomis gibbosus on the Iberian Peninsula, life-history attributes of pumpkinseed populations from Spanish water bodies were compared to populations in the northern and southern parts of its native range, as well as to those of English water bodies where introduced populations have shown minimal natural range expansion. Discriminate function analysis using five population characteristics [mean age at maturity, mean total length ( L _T) at maturity, gonado-somatic index ( I _G), mean L _T at age 2 years as an indication of juvenile growth rate and relative body condition] strongly differentiated populations from the four regional study areas. Spanish populations were early maturing, showed moderate juvenile growth rate and L _T at maturity and high I _G relative to the other population groups. Spanish populations matured significantly earlier than Canadian and English populations, but not southern U.S.A. populations. Spanish populations, however, had a significantly higher I _G than southern U.S.A. populations, suggesting greater reproductive output. Considering these differences in the context of the Winemiller and Rose triangular life-history strategy model, the pumpkinseed exhibits 'equilibrium' life-history traits that have made other non-native fishes successful invaders in areas where habitat alteration has resulted in more predictable discharge regimes and water levels. Populations in Iberia, however, appear to have achieved their success by adopting a more 'opportunistic' life-history strategy than their native counterparts. High levels of life-history plasticity appear to contribute to the success of this species on the Iberian Peninsula.     

Know when to run,know when to hide: can behavioral differences explain the divergent invasion success of two sympatric lizards?

Invasive species represent a select subset of organisms that have successfully transitioned through each stage of the introduction process (transportation, establishment, and spread). Although there is a growing realization that behavior plays a critical role in invasion success, few studies have focused on the initial stages of introduction. We examined whether differences in the grouping tendencies and exploratory behavior of two sympatric lizard species could contribute to their divergent invasion success. While the nondirected activity of the two species did not differ, the invasive delicate skink (Lampropholis delicata) was found to be more exploratory than the congeneric noninvasive garden skink (L. guichenoti), which enabled it to more effectively locate novel environments and basking site resources. The delicate skink also exhibited a greater tendency to hide, which may act to enhance its probability of ensnarement in freight and cargo and decrease its likelihood of detection during transit. The grouping tendencies of the two species did not differ. Together, our results suggest that while the two species have an equivalent "opportunity" for unintentional human-assisted transportation, several pre-existing behavioral traits may enhance the success of the delicate skink in negotiating the initial stages of the introduction process, and subsequent post-establishment spread.     

How can the feeding habits of the sand tiger shark influence the success of conservation programs?

The feeding habits of the sand tiger shark Carcharias taurus , one of the most threatened sharks of the world, are poorly known. Sand tiger sharks are critically endangered in the South-west Atlantic. Since 2007, the law requires that all individuals caught in recreational fisheries off Argentina must be released. Using data from a north Patagonian recreational fishery ( n =164 stomachs with contents), we analyzed the diet of sand tiger sharks in relation with size, sex, maturity stage and season; assessed prey consumption patterns and hooking location; and estimated diet overlap with fishery landings. Sand tiger sharks consumed mainly teleosts (55.4% of the total prey number, N ) and elasmobranchs (41.84% N ), and ate more benthic elasmobranchs (batoids and angel sharks) as they become larger. Sharks swallowed prey mostly in one piece (93.7%) and were hooked mainly in internal organs (87.4%, n =175), causing occlusion and perforation of the esophagus and stomach, and lacerations to the pericardium, heart and liver. Sand tiger sharks fed on the most heavily landed species, overlapping almost completely (>90%) with fishery landings. Conservation plans should take into account that releasing hooked sharks could be insufficient to minimize fishing mortality and that competition for food with fisheries is likely to occur.     

Can germination explain the distribution of tree species in a savanna wetland?

The relationship between seed germination and ecological niche is determined by matching germination characteristics with environmental features. In this study, we selected tree species occurring in the largest savanna wetland in South America – the Pantanal. Very few species are endemic or exclusively found in savanna wetlands, and the majority of tree species occurring in the Pantanal are also found in the neighbouring Brazilian Cerrado, a drier vegetation type that does not flood. We investigated the relationship between germination characteristics and occurrence of savanna trees in wetlands testing the hypothesis that such seeds are tolerant to flooding. We also addressed the question of whether seed tolerance to flood, assessed by survival analysis, explains tree distribution along a gradient of flooding intensity. In this flooding gradient, widely distributed species are those that occur in areas subjected to low as well as to high flooding intensity whereas restricted distributed species are those that occur only in areas subjected to a low level of flood. Seeds from tree species occurring in areas subjected to different flooding intensities were collected. Seed tolerance and germination during and after both one and two months of simulated flood were evaluated. Our results show that seeds of most of the studied savanna species tolerated submergence, which helps to explain their occurrence and wide distribution in wetlands. Nevertheless, germination behaviour checked by survival functions (i.e. how germination is distributed over time) partially explained tree species distribution along a flooding gradient. We conclude that seed tolerance to flooding is one of the components of the regeneration niche that determines tree occurrence and distribution at the regional scale, from savanna to wetland, but not at a local scale along a flooding gradient.     

Where can introduced populations learn their tricks? Searching for the geographical source of a species introduction to the Galápagos archipelago

We seek to understand the potential genetic impact of introduced species in an ecosystem where conservation efforts and pressure from development co-occur: the Galápagos Archipelago. To date, the introduced weevil Galapaganus h. howdenae is found only in Santa Cruz Island; however it has recently expanded its range beyond the Agricultural Zone into the highlands. We are focusing on comparisons between continental and introduced populations to clarify whether the current genetic patterns in introduced populations can reflect recovery from a past bottleneck and predict its invasive potential. A second objective is to narrow down the geographic source of the introduction and confirm their origin from a single introduction pulse. We found comparable microsatellite genetic diversity featuring many island-specific alleles, but reduced mitochondrial haplotype diversity in the islands. Additionally, both markers showed signals of population expansion and homogeneously distributed variation in the introduced range, in contrast to structured continental populations. The addition of mitochondrial sequences to the microsatellite dataset in the Approximate Bayesian Computation analyses (Diyabc) favors a single introduction pulse from the Northern Manabí area; a scenario that is in agreement with the haplotype network. An origin from higher elevation habitats provides clues about the environmental amplitude of the naturalized populations. However, given that a large percentage of the microsatellite variation in island populations is due to new island alleles, the answer to the question “where can introduced populations learn their tricks?” could be: right at their new location.     

UV-induced changes in the skin: can they be repaired?

The damaging effects of UVB light have been described previously and include a number of changes to multiple cell types. At previous meetings of this society, we have shown that Langerhans' cells are the most susceptible to UVB induced damage which can be shown as ultrastructural changes in dendrites, nucleus and cytoplasm by transmission electron microscopy. We have also shown that their patterns of migration from skin to regional lymph node and their ability to present antigens to autologous T cells have been profoundly altered by UVB irradiation. The aim of this work was to establish if it was possible to reverse any of the damage done to Langerhans' cells by UVB exposure by topical application of a DNA repair enzyme such as T4N5 endonuclease. These experiments were undertaken in a sheep model that allowed collection of cells as they migrate from the skin. This allowed for a direct examination of the migration characteristics and ultrastructural features of all Langerhans' cells before, during, and for 2 weeks after exposure to a single dose of UVB. Results obtained from this project indicate that treatment by topical application of DNA repair enzyme immediately after UVB irradiation may restore a number of normal immune parameters associated with the structure and function of migrating Langerhans' cells. It appears that there is a dose related correction of the increased tempo of cell migration and some improvements in the number of ultrastructurally damaged Langerhans' cells have also been associated with application of higher doses of DNA repair enzyme. These preliminary findings indicate that some potential therapeutic benefits are associated with the use of such agents in reversing the immunological damage caused by exposure to erythemal doses of UVB light.     

Can transgenerational plasticity contribute to the invasion success of annual plant species?

Adaptive transgenerational plasticity (TGP), i.e., significantly higher fitness when maternal and offspring conditions match, might contribute to the population growth of non-native species in highly variable environments. However, comparative studies that directly test this hypothesis are lacking. Therefore, we performed a reciprocal split-brood experiment to compare TGP in response to N and water availability in single populations of two invasive (Amaranthus retroflexus, Galinsoga parviflora) and two congeneric non-invasive introduced species (Amaranthus albus, Galinsoga ciliata). We hypothesized that the transgenerational effect is adaptive: (1) in invasive species compared with non-invasive adventives, and (2) in stressful conditions compared with resource-rich environments. The phenotypic variation among offspring was generated, in large part, by our experimental treatments in the maternal generation; therefore, we demonstrated a direct TGP effect on the offspring’s adult fitness. We found evidence, for the first time, that invasive and non-invasive adventive species differ regarding the expression of TGP in the adult stage, as adaptive responses were found exclusively in the invasive species. The manifestation of TGP was more explicit under resource-rich conditions; therefore, it might contribute to the population dynamics of non-native species in resource-rich sites rather than to their ecological tolerance spectra.