Effects of nonnative species on the stability of riverine fish communities

ResearchDespite the increasing ubiquity of biological invasions worldwide, little is known about the scale-dependent effects of nonnative species on real-world ecological dynamics. Here, using an extensive time series dataset of riverine fish communities across different biogeographic regions of the world, we assessed the effects of nonnative species on the temporal variability and synchrony in abundance at different organizational levels (population, metapopulation, community and metacommunity) and spatial scales (stream reach and river basin). At the reach scale, we found that populations of nonnative species were more variable over time than native species, and that this effect scaled up to the community level – significantly destabilizing the dynamics of riverine fish communities. Nonnative species not only contributed to reduced community stability, but also increased variability of native populations. By contrast, we found no effect of nonnative species dominance on local interspecific synchrony among native species. At the basin scale, nonnative metapopulations were again more variable than the native ones. However, neither native metapopulations nor metacommunities showed differences in temporal variability or synchrony as nonnative species dominance increased basin-wide. This suggests a ‘dilution effect’ where the contribution to regional stability of local native populations from sites displaying low levels of invasion reduced the destabilizing effects of nonnative species. Overall, our results indicate that accounting for the destabilizing effect of nonnative species is critical to understanding native species persistence and community stabilityinfo:eu-repo/semantics/publishedVersio

Effects of nonnative species on the stability of riverine fish communities

13openInternationalInternational coauthor/editorDespite the increasing ubiquity of biological invasions worldwide, little is known about the scale‐dependent effects of nonnative species on real‐world ecological dynamics. Here, using an extensive time series dataset of riverine fish communities across different biogeographic regions of the world, we assessed the effects of nonnative species on the temporal variability and synchrony in abundance at different organizational levels (population, metapopulation, community and metacommunity) and spatial scales (stream reach and river basin). At the reach scale, we found that populations of nonnative species were more variable over time than native species, and that this effect scaled up to the community level – significantly destabilizing the dynamics of riverine fish communities. Nonnative species not only contributed to reduced community stability, but also increased variability of native populations. By contrast, we found no effect of nonnative species dominance on local interspecific synchrony among native species. At the basin scale, nonnative metapopulations were again more variable than the native ones. However, neither native metapopulations nor metacommunities showed differences in temporal variability or synchrony as nonnative species dominance increased basin‐wide. This suggests a ‘dilution effect’ where the contribution to regional stability of local native populations from sites displaying low levels of invasion reduced the destabilizing effects of nonnative species. Overall, our results indicate that accounting for the destabilizing effect of nonnative species is critical to understanding native species persistence and community stabilityopenErős, T.; Comte, L.; Filipe, A.F.; Ruhi, A.; Tedesco, P.A.; Brose, U.; Fortin, M.J.; Giam, X.; Irving, K.; Jacquet, C.; Larsen, S.; Sharma, S.; Olden, J.D.Erős, T.; Comte, L.; Filipe, A.F.; Ruhi, A.; Tedesco, P.A.; Brose, U.; Fortin, M.J.; Giam, X.; Irving, K.; Jacquet, C.; Larsen, S.; Sharma, S.; Olden, J.D

Nitrogen and sulphur management: challenges for organic sources in temperate agricultural systems

A current global trend towards intensification or specialization of agricultural enterprises has been accompanied by increasing public awareness of associated environmental consequences. Air and water pollution from losses of nutrients, such as nitrogen (N) and sulphur (S), are a major concern. Governments have initiated extensive regulatory frameworks, including various land use policies, in an attempt to control or reduce the losses. This paper presents an overview of critical input and loss processes affecting N and S for temperate climates, and provides some background to the discussion in subsequent papers evaluating specific farming systems. Management effects on potential gaseous and leaching losses, the lack of synchrony between supply of nutrients and plant demand, and options for optimizing the efficiency of N and S use are reviewed. Integration of inorganic and organic fertilizer inputs and the equitable re-distribution of nutrients from manure are discussed. The paper concludes by highlighting a need for innovative research that is also targeted to practical approaches for reducing N and S losses, and improving the overall synchrony between supply and demand

Acceleration effect of coupled oscillator systems

We have developed a curved isochron clock (CIC) by modifying the radial isochron clock to provide a clean example of the acceleration (deceleration) effect. By analyzing a two-body system of coupled CICs, we determined that an unbalanced mutual interaction caused by curved isochron sets is the minimum mechanism needed for generating the acceleration (deceleration) effect in coupled oscillator systems. From this we can see that the Sakaguchi and Kuramoto (SK) model which is a class of non-frustrated mean feild model has an acceleration (deceleration) effect mechanism. To study frustrated coupled oscillator systems, we extended the SK model to two oscillator associative memory models, one with symmetric and one with asymmetric dilution of coupling, which also have the minimum mechanism of the acceleration (deceleration) effect. We theoretically found that the {\it Onsager reaction term} (ORT), which is unique to frustrated systems, plays an important role in the acceleration (de! celeration) effect. These two models are ideal for evaluating the effect of the ORT because, with the exception of the ORT, they have the same order parameter equations. We found that the two models have identical macroscopic properties, except for the acceleration effect caused by the ORT. By comparing the results of the two models, we can extract the effect of the ORT from only the rotation speeds of the oscillators.Comment: 35 pages, 10 figure

Buffering and trophic mismatch in spring-feeding forest caterpillars

Across temperate environments, climate warming is leading to a general advancement of spring phenology in a wide range of ecologically and taxonomically diverse species. For taxa that depend on interactions with other species—predators and prey, pollinators, parasites and hosts—widespread phenological changes may cause severe problems. Divergent phenological responses to spring temperature changes among taxa could result in these crucial biotic interactions becoming mistimed. This may cause significant negative fitness effects that could ripple through a population, across trophic levels, and perhaps entire ecosystems. This concept, formalised as the match-mismatch hypothesis (MMH) has become the subject of intense speculation and debate in recent decades. Much of our understanding of the occurrence and significance of ‘phenological mismatch’ (negative fitness consequences brought about by mistiming between interacting species) due to climate change comes from the trophic interactions in the classic temperate woodland tree/caterpillar/bird food-chain. This work, however, suffers from many limitations. Spring-feeding caterpillars, forming the central link in this food-chain, are particularly important in that fluctuations in their populations can affect both higher and lower trophic levels. In the tree/caterpillar link, previous literature focuses largely on a single host and caterpillar species pairing: oak (Quercus robur) and the winter moth (Operophtera brumata). It has been argued that these caterpillars could respond more strongly than their host-plants to climate warming in terms of shifting their phenology, and that even slight mistiming between the two trophic levels has significant negative fitness effects for them. Caterpillars that hatch before bud-burst on their host tree will likely starve, and those that hatch too late are forced to feed on less palatable mature foliage. This rather narrow view, however, overlooks the fact that these caterpillars may be resilient to mistiming in many instances, and that the oak/winter moth trophic interaction may not necessarily be representative of the many other caterpillar species, or alternative host-plant species. In this thesis, I attempt to expand our knowledge and understanding of the operation of the MMH in this system by specifically addressing some of these key caveats. First, in Chapter 2, in order to address the role of different plant species in the diet of the winter moth and the relative importance of oak as a host-plant species, I consider the effects of host-plant species on survival, growth, and development of the caterpillars, across four British populations. I find that winter moth caterpillar fitness varies substantially across host-plant species, but that there are also strong population-specific responses consistent with genetic divergence. In contrast to the assumptions typically made in the literature that oak is the “primary”, “principal”, or most significant host-plant species in the field, I find that caterpillar performance on this species is consistently poor relative to other abundant and widespread host-plant species. Reconciling this apparent inconsistency represents an obvious avenue for future research. A taxonomically broad diet may serve to buffer winter moth caterpillars against the effects of mismatch on any one host-plant species—phenology varies across hosts and, averaged across a population, this might ensure there are always some food resources available for individuals to exploit. Next, in Chapters 3 and 4, to determine whether the impacts of mismatch generalise across caterpillar and host-plant species, I directly test the effects of mistiming across a range of British spring-feeding caterpillar species, including the winter moth. In Chapter 3, I consider the effects of late-hatching asynchrony on performance (and fitness in the winter moth) of up to 65 days. I find that the effects of asynchrony on performance are contingent on the particular caterpillar/host-plant species pairing in question. Depending on the host-plant species, some caterpillar species show little to no decline in performance across a period of several months (e.g. vapourer Orgyia antiqua on birch Betula pendula or sycamore Acer pseudoplatanus), while others show precipitous declines in a matter of days (e.g. fitness in winter moth on sycamore or sallow Salix caprea). This highlights the danger of extrapolating from a single caterpillar/host-plant species pairing. Indeed, in both cases, the winter moth and oak appear to be exceptional—performance of the former typically showing a steeper than average decline with increasing asynchrony, and the latter being a generally poor host for most spring-feeding caterpillar species, on which performance declines at a greater rate than other host-plants with asynchrony. Overall, I find that, in contrast to the prevailing view in the literature, synchrony is important for caterpillar fitness, but within fairly broad bounds (at a scale of weeks and months, rather than days), though this varies across hosts and species. In Chapter 4, I consider asynchrony in the opposite direction, and investigate the ability of spring-feeding caterpillars to cope with hatching too early, before bud-burst on their natal tree. Early hatching caterpillars can simply tolerate a lack of food and wait until it becomes available, or they may be able to exploit the unopened buds of their host-plants as a food source in the intervening period. I found that across five spring-feeding caterpillar species, there is often a considerable ability to tolerate starvation, ranging from several days in the winter moth and mottled umber Erannis defoliaria, to over thirty in the black arches Lymantria monacha. Increased temperatures, however, significantly reduced the time which caterpillars could survive without food, often by a substantial margin (e.g. by twenty days in the black arches moth at temperatures of 21°C versus 5°C). In the winter moth, I show experimentally for the first time that caterpillars are indeed able to feed on the unopened and opening buds of a range of their host-plant species. However, the likelihood of establishment on buds is initially low and increases steeply as buds mature and softer tissue becomes more exposed. Nonetheless, this clearly demonstrates that many spring-feeding caterpillar species have at least some ability to tolerate early hatching on their host tree. In Chapter 5, I consider in more detail the widely-held assumption that foliage becomes unsuitable for caterpillar consumption very soon after bud-burst. In contrast to Chapter 3, I reared caterpillars on frozen foliage collected from a sample of trees across a two week period after bud-burst, to determine the effects of any changes in their structure and secondary chemistry across this period on palatability. Specifically, I focussed here on the effects of caterpillar asynchrony on growth rate and rate of survival across time, both of which have distinct fitness implications versus overall mass attained or survival probability (cf. Chapter 3). I find no consistent effects of leaf age on rates of mortality across time, suggesting that leaf maturation occurring within the first two weeks after bud-burst generally has little effect on caterpillar performance. There are, however, significant effects of host-plant species and age on growth rates—on older oak foliage, growth rates are higher, the implications of which are unclear. Additionally, I find that there is substantial variation in caterpillar performance between individual trees and broods. Taken together, these findings may indicate that phenological variation between individual trees could serve to ameliorate mismatch, buffering against it at the population level. Finally, in Chapter 6, I discuss the concept of ‘buffering’ in detail—a phrase widely used but little considered. I argue that buffering is related to concepts of stability in living systems, and that it represents the means by which stability is maintained, via a range of ‘buffering mechanisms’. I define buffering as “the amelioration of any fitness effects resulting from an environmental change”. I explore the concept specifically within the spring-feeding caterpillar system, and argue that the very unpredictability and uncertainty that is an inherent part of their niche has driven the evolution of many of the buffering mechanisms by which that variation can be tolerated. By extension, I propose that a predisposition to tolerating environmental uncertainty may mean these species will be buffered against at least some of the negative effects of future climate change, such as an increased incidence of asynchrony. Taken together, my analyses suggest that the overwhelming focus placed on the winter moth/oak interaction in literature on the MMH is likely to be misleading—these taxa are not necessarily representative of other species at these trophic levels in the woodland food web, and the effects of asynchrony on caterpillar performance and fitness is highly contingent on both taxa involved. It is therefore difficult and perhaps unwise to make excessively broad generalisations about the effects of climate change on the broader spring-feeding caterpillar guild, and any cascading effects to other species with which they interact. Contrary to the widespread view in the literature, the caterpillars of a range of moth species seem able to cope with at least some degree of both early- and late-hatching asynchrony: by feeding on a range of host-plant species; by tolerating more mature foliage; by tolerating starvation when food is unavailable; and, by utilising the young, unopened buds of their host-plants as food. These traits may equally well buffer caterpillars against potential mismatch resulting from divergent phenological responses to future climatic change relative to their host-plants. More broadly, this particular instance highlights the potential general importance of buffering as a phenomenon in other groups of organisms, where it could play a key role in ameliorating some of the negative effects of climate change

Environmental Drivers of Morphological and Physiological Adaptation in an Invasive Defoliator, Lymantria Dispar

Climatic gradients result in life-history tradeoffs across diverse taxa. Studying range-expanding invasive species can offer insight to environmental conditions that drive adaptive responses. Insects, which have rapid generations and high fecundity, can adapt rapidly to novel or changing environmental conditions, making them ideal model organisms for studying evolution in situ. European gypsy moth was introduced to North America in 1869 near Boston, Massachusetts, USA, and has since expanded its range to occupy 12 ̊ of latitude and diverse thermal regimes. I investigated environmental drivers of adaptation across the latitudinal-climatic range of gypsy moth in North America. I linked variation in wing length, a proxy for body size, of pheromone-trapped males to metrics of habitat quality including forest composition, phenology, and population density. I found support for previously reported seasonal phenology-linked decline in wing length in both endemic and outbreaking gypsy moth populations. Furthermore, I found significant differences in wing length between males from forests of different quality by using discrete forest quality estimates, but not using continuous metrics of forest quality. Mean wing length of males from outbreak populations was smaller on than those from endemic populations. Male flight capacity is an important aspect of fitness, and has important implications for mate- finding and establishment success during range expansion. Using fixed-arm flight mills, I found that body size is the most important predictor for total flight distance and maximum speed, and forewing aspect and relative thorax mass also had a significant effect on flight capacity. Using a reciprocal transplant study, I found evidence for adaptive shifts in hatch timing occurring in populations from across the latitudinal range of gypsy moth, which may serve to reduce asynchrony with budburst of preferred host tree species at latitudinal range margins. I demonstrated that fitness costs of hatching ahead of or behind red oak budburst may provide sufficient selective pressures to drive the change observed in natural populations. The results herein may inform current gypsy moth management priorities, and identify knowledge gaps where future research can improve our understanding of the barriers to range expansion in gypsy moth and perhaps other invasive species