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Interaction between invasive plant leaf litter and NaCl on two model amphibians

DOI:10.1007/s10530-018-1836-7
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Devin Gottardo Digiacopo at Binghamton University
Devin Gottardo Digiacopo
George A Meindl at University of Wisconsin–Madison
George A Meindl
Sean Ryan
Sean Ryan
Sean Ryan
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Jared Jaeger
Jared Jaeger
Jared Jaeger
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Abstract and Figures

Human activities are rapidly changing natural environments, often with harmful consequences for native communities. The introduction of invasive species is particularly damaging to native communities, especially when invasive species alter the chemical environment and create novel, stressful conditions. These abiotic conditions are predicted to favor other stress-tolerant organisms, potentially shifting community abundance and diversity over time. However, few environments are free of other anthropogenic stressors (i.e., chemical contaminants), which can also influence patterns of abundance and diversity. Therefore, to understand the impacts of invasive species, we need to consider their potential interactions with other anthropogenic stressors. Towards this goal, we tested how leachates from invasive plants and road salt impacted a model amphibian that is native to the U.S. (northern leopard frog, Lithobates pipiens) and a model amphibian that is non-native to the U.S. and considered invasive in some localities (African clawed frog, Xenopus laevis). We examined the effects of native and invasive leaf litter leachate and sublethal NaCl concentrations on amphibian development, size, and tolerance to a lethal concentration of NaCl. Exposure to invasive leaf litter and sublethal NaCl both accelerated hatching time in leopard frogs, but neither affected hatching time in Xenopus. Exposure to invasive leaf litter also led to reduced mass and tolerance to lethal NaCl concentrations in the leopard frog, but had no effect on mass and led to increased tolerance to lethal NaCl concentrations in Xenopus. These findings suggest that invasive leaf litter leachate impacts these amphibian species differently, being more stressful to the leopard frog than Xenopus. Further, we demonstrate that the presence of a pollutant may augment the effect of invasive leaf litter on amphibians, highlighting the need to consider concurrent stressors in invasive species management.
Developmental stages of Lithobates pipiens (leopard frog) and Xenopus laevis (African clawed frog). We defined hatching in the TTH experiment when the individual emerged from the egg case (Gosner stage 20 for leopard frogs and N&F stage 41 for Xenopus)
Developmental stages of Lithobates pipiens (leopard frog) and Xenopus laevis (African clawed frog). We defined hatching in the TTH experiment when the individual emerged from the egg case (Gosner stage 20 for leopard frogs and N&F stage 41 for Xenopus)
… 
Plant leaf litter treatment groupings based on factor and cluster analyses. Native plants (steeple bush—StB, cattail—Cat, huckleberry—Hkb) are grouped within the solid circle and invasive plants (common reed—CRe, purple loosestrife—Plo, autumn olive—AOl) by dotted line
Plant leaf litter treatment groupings based on factor and cluster analyses. Native plants (steeple bush—StB, cattail—Cat, huckleberry—Hkb) are grouped within the solid circle and invasive plants (common reed—CRe, purple loosestrife—Plo, autumn olive—AOl) by dotted line
… 
Abiotic variables in native versus invasive leaf litter treat. a Water quality measures (dissolved oxygen, turbidity, and pH) in native versus invasive leaf litter treatments. b ICPMS metal concentrations (alkali, alkaline, and transition metals) and general hardness (a combined measure of magnesium and calcium [see appendix for calculation]; mg L⁻¹) in native versus invasive leaf litter treatments. The * symbol represents treatments that differ significantly (p < 0.05)
Abiotic variables in native versus invasive leaf litter treat. a Water quality measures (dissolved oxygen, turbidity, and pH) in native versus invasive leaf litter treatments. b ICPMS metal concentrations (alkali, alkaline, and transition metals) and general hardness (a combined measure of magnesium and calcium [see appendix for calculation]; mg L⁻¹) in native versus invasive leaf litter treatments. The * symbol represents treatments that differ significantly (p < 0.05)
… 
Time to hatching for leopard frogs and Xenopus reared in native or invasive leaf litter. The * symbol represents treatments that differ significantly (p < 0.05)
Time to hatching for leopard frogs and Xenopus reared in native or invasive leaf litter. The * symbol represents treatments that differ significantly (p < 0.05)
… 
Time to death following exposure to a lethal concentration of NaCl (10 g L⁻¹) for leopard frogs and Xenopus tadpoles that were pre-exposed to 0 or 1 g L⁻¹ of NaCl and reared in native versus invasive leaf litter as embryos and hatchlings. The * symbol represents treatments that differ significantly (p < 0.05)
+1
Time to death following exposure to a lethal concentration of NaCl (10 g L⁻¹) for leopard frogs and Xenopus tadpoles that were pre-exposed to 0 or 1 g L⁻¹ of NaCl and reared in native versus invasive leaf litter as embryos and hatchlings. The * symbol represents treatments that differ significantly (p < 0.05)
… 
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ORIGINAL PAPER
Interaction between invasive plant leaf litter and NaCl
on two model amphibians
Devin G. DiGiacopo .George A. Meindl .Sean Ryan .Jared Jaeger .
Matthew Wersebe .Amelia Martin .Seth A. Robinson .Gabrielle Graham .
Adam R. Palmer .Amanda Setteducate .Ian Murray .Kirsten Prior .
Jessica Hua
Received: 2 April 2018 / Accepted: 30 August 2018 / Published online: 10 September 2018
ÓSpringer Nature Switzerland AG 2018
Abstract Human activities are rapidly changing
natural environments, often with harmful conse-
quences for native communities. The introduction of
invasive species is particularly damaging to native
communities, especially when invasive species alter
the chemical environment and create novel, stressful
conditions. These abiotic conditions are predicted to
favor other stress-tolerant organisms, potentially
shifting community abundance and diversity over
time. However, few environments are free of other
anthropogenic stressors (i.e., chemical contaminants),
which can also influence patterns of abundance and
diversity. Therefore, to understand the impacts of
invasive species, we need to consider their potential
interactions with other anthropogenic stressors.
Towards this goal, we tested how leachates from
invasive plants and road salt impacted a model
amphibian that is native to the U.S. (northern leopard
frog, Lithobates pipiens) and a model amphibian that
is non-native to the U.S. and considered invasive in
some localities (African clawed frog, Xenopus laevis).
We examined the effects of native and invasive leaf
litter leachate and sublethal NaCl concentrations on
amphibian development, size, and tolerance to a lethal
concentration of NaCl. Exposure to invasive leaf litter
and sublethal NaCl both accelerated hatching time in
leopard frogs, but neither affected hatching time in
Xenopus. Exposure to invasive leaf litter also led to
reduced mass and tolerance to lethal NaCl concentra-
tions in the leopard frog, but had no effect on mass and
led to increased tolerance to lethal NaCl concentra-
tions in Xenopus. These findings suggest that invasive
leaf litter leachate impacts these amphibian species
differently, being more stressful to the leopard frog
than Xenopus. Further, we demonstrate that the
presence of a pollutant may augment the effect of
invasive leaf litter on amphibians, highlighting the
need to consider concurrent stressors in invasive
species management.
Keywords Xenopus laevis African clawed frog
Lithobates pipiens Northern leopard frog
Contaminant Salt
Devin G. DiGiacopo and George A. Meindl have contributed
equally to this work.
Electronic supplementary material The online version of
this article (https://doi.org/10.1007/s10530-018-1836-7) con-
tains supplementary material, which is available to authorized
users.
D. G. DiGiacopo (&)G. A. Meindl
S. Ryan J. Jaeger M. Wersebe A. Martin
S. A. Robinson G. Graham A. R. Palmer
A. Setteducate I. Murray K. Prior J. Hua
Biological Sciences Department, Binghamton University
(SUNY), 4400 Vestal Parkway East,
PO Box 6000, Binghamton, NY 13902, USA
e-mail: ddigiac1@binghamton.edu
123
Biol Invasions (2019) 21:391–403
https://doi.org/10.1007/s10530-018-1836-7(0123456789().,-volV)(0123456789().,-volV)
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... For example, Waitling et al. [15] found that toads reared in invasive plant extracts experienced higher mortality compared to toads reared in native plant extracts. Similarly, in a recent study, DiGiacopo et al. [16] demonstrated that changes to water chemistry due to leachates from native vs. invasive leaf litter can modify amphibian development and survival. Specifically, when leopard frogs were reared in solutions containing invasive plant leachates vs. native leachates, they hatched earlier and were more susceptible to lethal doses of NaCl as tadpoles. ...
... Given that African clawed frogs have been shown to be more tolerant to invasive species leachates and NaCl relative to leopard frogs [16], we predict that African clawed frogs will be more tolerant to increasing metal concentrations and subsequent exposure to increasing salinity compared to leopard frogs. ...
... Control solutions consisted of UVtreated, filtered well water. Low and high treatment solutions for all elements were created using chloride salts, and concentrations were determined based on previous work reflecting element concentrations in leachate solutions created using several native and invasive wetland plants in New York State [16]. More specifically, the low treatments mimic native plant chemistry, while the high treatments mimic invasive plant chemistry. ...
Exposure to metals (Ca, K, Mn) and road salt (NaCl) differentially affect development and survival in two model amphibians
Article
  • Jan 2020
Human activity has led to widespread chemical alteration of natural environments. Aquatic ecosystems are especially susceptible to chemical changes, including those caused by runoff and invasive species. Here, we examined the effects of water chemistry, specifically sodium chloride as well as three metals (Ca, K, and Mn) known to differ between native and invasive wetland plant species’ leaf tissues, on the development of two model amphibians: the native Northern leopard frog, Lithobates pipiens, and the non-native African clawed frog, Xenopus laevis. We exposed frog eggs to metal treatment solutions and measured time to hatching (TTH), and following hatching, we exposed tadpoles to a lethal concentration of sodium chloride and recorded time to death (TTD). We found that increasing metal concentrations generally resulted in acceleration of TTH for Xenopus tadpoles, but had no effect on leopard frogs. However, increasing metal concentrations (Ca, Mn) increased leopard frog tadpole susceptibility to NaCl (decreased TTD), while increasing metal concentrations (Ca, K) generally resulted in decreased Xenopus tadpole susceptibility to NaCl. Overall, our data suggest that invasive amphibians may be more tolerant to chemical changes than native amphibians, including those driven by the introduction of invasive plant species.
View
... Proposed as a mechanism to deter herbivory during periods when fewer native leaves are available to herbivores (Fridley 2012;Borth et al. 2018), this pattern consequently increases leaf toxicity at or near senescence, coinciding with peak periods of deposition into aquatic systems. Larval amphibian and invertebrate communities also exhibit temporally staggered breeding phenologies (Petranka 1998;Dodd 2013) and differ considerably in their responses to secondary compounds of invasive plant species (Martin and Blossey 2013;DiGiacopo et al. 2019;Iglesias-Carrasco et al. 2022). Consequently, the specific timing of senescence in L. maackii, coupled with considerations regarding which species are present and/or vulnerable to exposure, will likely mediate net effects on aquatic communities. ...
Leaves of an invasive shrub induce mass mortality of an amphibian apex predator and its macroinvertebrate prey
Article
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Studies of plant invasions have primarily focused on effects within shared habitats of native and invasive species. However, secondary compounds produced by terrestrial invasive plants can cross terrestrial-aquatic boundaries via senesced leaves, leading to altered patterns of aquatic biodiversity and ecosystem functioning. Impacts of phenolic compounds from senesced leaves have been characterized among relatively lower trophic groups, but effects on keystone species, such as apex predators, should have disproportionately larger effects on aquatic food webs. Using a widespread invasive species (Amur Honeysuckle, Lonicera maackii), we employed experimental mesocosms to examine effects of honeysuckle leaf litter addition on survival of apex predators (larval spotted salamanders, Ambystoma maculatum), their zooplankton and macroinvertebrate prey, indicators of primary productivity and decomposition, and abiotic variables influenced by phenolic compounds. Despite previous laboratory observations suggesting A. maculatum might exhibit resistance to L. maackii leachates, we observed near complete loss of both A. maculatum and benthic macroinvertebrates in experimental mesocosms, while zooplankton abundance was unaffected. Mortality was likely associated with precipitous declines in dissolved oxygen following rapid decomposition of L. maackii leaves, and these conditions facilitated nearly 15-fold increases in larval mosquito abundance. Our results highlight how experimental venue and methodology may alter outcomes of investigations involving senesced leaves of invasive plants. Losses of amphibian predators under quasi-natural invasion conditions indicate important influences on terrestrial-aquatic nutrient exchange, and we highlight phenological patterns of leaf senescence and breeding by aquatic organisms as important avenues for further investigation in characterizing the consequences of plant invasions.
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... As exotic invasive species are a major driver of plant community change (Zedler and Kercher 2004), we examined two pairs of native and invasive plants that share similar habitat preferences (black huckleberry [Gaylussacia baccata-Ericaceae] versus autumn olive [Elaeagnus umbellata-Elaeagnaceae] and swamp loosestrife [Decodon verticillatus-Lythraceae] versus purple loosestrife [Lythrum salicaria-Lythraceae]). We utilized anuran larvae as our focal taxa for this study because previous studies have demonstrated a broad range of direct and indirect effects-ranging from sublethal (e.g., altered growth, development and behavior Brown et al. 2006;Saenz and Adams 2017;DiGiacopo et al. 2018) to lethal (i.e., reduced survival; Adams and Saenz 2012;Milanovich et al. 2016)-of changes in leaf litter composition on anurans. Therefore, in this study, we evaluated the effects of leaf litter type on amphibian ecology, including competitive, predator-prey and host-parasite interactions. ...
The effects of novel leaf litter deposition on competitive, predator–prey and host–parasite interactions of American toad larvae
Article
Full-text available
Wetland plant communities are changing rapidly due to a wide range of human activities. The deposition of leaf litter from novel plant communities can alter both the chemical and physical habitat of aquatic ecosystems. Lesser understood are the ecological consequences of novel leaf litter inputs in aquatic communities. Toward this goal, we used two plant invasion scenarios (comparing native black huckleberry to exotic autumn olive and native swamp loosestrife to exotic purple loosestrife) to simulate a shift in wetland plant communities. In this study, we investigated the effects of novel leaf litter leachates on three aquatic ecological interactions: intraspecific competition, predation and parasitism. We examined how leaf litter leachates influence the interactions of American toad larvae (Anaxyrus americanus) with their conspecifics, a dragonfly predator (Anax spp.) and a trematode parasite (Echinostomatidae). We found that leaf litter type influenced competitive interactions only for the huckleberry versus autumn olive comparison. We did not detect any effects of leaf litter type on predator–prey interactions. Finally, litter type strongly influenced host–parasite interactions for both leaf litter comparisons, altering host susceptibility, parasite survival and net infection rates. These results highlight the breadth of potential ecological repercussions of shifting wetland plant communities for native ecosystems.
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... Amphibian responses to invasive plants appear to be species-specific, but exposure to invasive plant leachates have resulted in decreased survival, developmental delays, population declines, deformities, and behavioral changes (e.g., Maerz et al. 2005;Watling et al. 2011;Greenberg and Green 2013;Martin et al. 2014;Burraco et al. 2018;DiGiacopo et al. 2019). Leaf litter from both invasive and native plants can alter water chemistry (pH, dissolved oxygen), release toxic leachates (which can alter predator recognition), reduce growth and size at metamorphosis, and interfere with metabolism, oxygen consumption, and hormone regulation (e.g., Lambert et al. 2017;Burraco et al. 2018;Stoler and Relyea 2020). ...
Increased Temperature Influenced Growth and Development of Lithobates pipiens Tadpoles Exposed to Leachates of the Invasive Plant European Buckthorn (Rhamnus cathartica) and a Triclopyr Herbicide
Article
Full-text available
  • Jun 2021
Multiple factors including habitat loss, pollutants, invasive species, and disease have contributed to the global decline of amphibians; and further declines can be expected as a result of climate change. Warming temperatures may allow for range expansion of invasive plants, and because herbicides are the primary method to control invasive plants, chemical use may increase. A laboratory experiment was performed to examine the individual and combined effects of leachates from the invasive plant European buckthorn (Rhamnus cathartica, L.) and a triclopyr herbicide This article is protected by copyright. All rights reserved. Accepted Article (Renovate® 3; 0.21 mg/L) commonly used to manage R. cathartica on northern leopard frog (Lithobates pipiens, Schreber) tadpoles at two temperature regimes (20°C and 25°C). We measured tadpole growth weekly and body and intestine morphology at the conclusion of the experiment after eight weeks. In the presence of R. cathartica leachates tadpole growth increased at 25°C, but only during the first 3-4 weeks of the experiment. From week 5 until the end of the experiment, tadpoles were significantly smaller at 25°C compared to 20°C, but had more developed limb buds at the end of the experiment (except in the triclopyr treatment). Triclopyr had minimal effects on tadpole growth. These results encourage further examination of potential effects of global climate changes in combination with other environmental factors that may impact amphibian populations.
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... Several studies have focused on amphibians, an indicator taxon useful in inferring the overall condition of many lentic ecosystems. These studies reported negative effects of invasive aquatic plants on early life stages of amphibians in laboratory studies, such as increased malformations and predation risk, impaired respiration, and decreased hatching success, survival, and growth of larvae (Adams & Saenz, 2012;Bucciarelli et al., 2014;Cohen et al., 2012;Cotten et al., 2012;DiGiacopo et al., 2019;Sacerdote & King, 2014;Watling et al., 2011). ...
Impacts of invasive Amur honeysuckle, Lonicera maackii, leaf litter on multiple trophic levels of detritus‐based experimental wetlands
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• Wetlands are especially vulnerable to invasive plants because seasonal movements of sediments, water, nutrients, and debris from adjacent terrestrial habitats create ecological conditions suitable for invasion. Lonicera maackii is a relatively abundant and broadly distributed invasive shrub in the eastern U.S.A., yet few studies have simultaneously tested for effects of its leaf litter on multiple trophic levels within wetland food webs. • Hatching success, hatchling survival, and hatchling size of tadpoles (Acris crepitans) were assessed using a laboratory mesocosm experiment with no-leaf, native-leaf, and L. maackii-leaf treatments. In the field, short-term (c. 3 week) and long-term (c. 2 years) mesocosm experiments assessed the initial and persistent impacts, respectively, of L. maackii on measures of primary productivity, invertebrate abundance and community structure, and oviposition preference and larval survival of Cope's gray treefrog (Hyla chrysoscelis). • Exposure of eggs to L. maackii leaves reduced body size at hatching and larval survival of newly hatched A. crepitans. In short-term experiments, L. maackii leaves reduced dissolved oxygen levels, filamentous algal biomass, and macroinvertebrate abundance, and altered macroinvertebrate community structure. In long-term experiments, duckweed cover was 15× times greater in mesocosms with L. maackii leaf additions. Oviposition by a local population of H. chrysoscelis was 10× lower in both short- and long-term mesocosms with L. maackii present. • Although ecological impacts of L. maackii have been reported for terrestrial systems, our study is the first to demonstrate the simultaneous effects of its leaves on multiple trophic levels within replicated experimental wetlands. The relatively rapid decomposition of L. maackii leaves, and associated pulse of phenolic compounds, is the most likely proximate mechanism of the bottom-up effects we observed. The mechanisms, timing, and significance of effects is predicted to vary among natural wetlands. • Our study demonstrates multiple ecological impacts of a terrestrial invasive shrub within experimental wetlands. Detailed studies on the specific mechanisms, and their spatial and temporal variability in natural systems, will elucidate management strategies and improve the efficiency of wetland conservation efforts.
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Current status of the invasive shrub Berberis julianae C.K. Schneid. (Berberidaceae) in Golden Gate Highlands National Park (Free State Province, South Africa)
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Berberis julianae commonly known as Wintergreen barberry or Chinese barberry, is an evergreen shrub species native to China which has been introduced into South Africa and has become invasive in a few locations. In 2015, management measures were taken in an attempt a control a population in Golden Gate Highlands National Park (GGHNP) in the Free State Province. After assessing the plant demographics within the park, the following management options were implemented: cut stump treatments of larger shrubs, foliar spray herbicide applications and hand pulling of seedlings. It was recommended that follow-up research be conducted to check if control measures were successful or not. This study aimed to map and determine the current distribution of B. julianae in GGHNP and to investigate the change in B. julianae population demographics to that recorded previously. The study showed that the number of seedlings had multiplied from 6 seedlings in 2014 to 588 in 2020, whereas the number of mature shrubs had decreased in the same time period. In conclusion, the control measures conducted have been successful in reducing the adult population, however, additional follow-up control of seedlings is urgently required to stop further spread.
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Reviewing the role of plant litter inputs to forested wetland ecosystems: leafing through the literature
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The input of senescent terrestrial leaf litter into soil and aquatic ecosystems is one of the most massive cyclic subsidies on Earth, particularly within forested ecosystems. For freshwater systems embedded within forests, litter inputs provide a vital source of energy and nutrients that allows greater production than in‐situ resources can provide. In return, freshwater food webs can provide an enormous amount of material to the terrestrial landscape through biotic respiration, photosynthesis, and organism emergence. Most research concerning this important aquatic‐terrestrial link has focused on lotic ecosystems (i.e., streams and rivers); far less attention has been given to its role in lentic systems (i.e., wetlands and lakes). A focus on small forested wetlands is particularly important, as these systems account for a disproportionate amount of global carbon flux relative to their spatial coverage, and the decomposition of leaf litter is a major contributor. Here, we review six themes: 1) the evidence for the role of leaf litter inputs as an ecologically important subsidy in forested wetlands; 2) the bottom‐up effects of quantitative and qualitative variation in litter inputs; 3) how diversity in litter mixtures can alter ecological functioning; 4) evidence for top‐down consequences of litter inputs through toxic effects on predators and parasites, and the alteration of predator‐prey interactions; 5) the relevance of our review to other research fields by considering the role of litter inputs relative to other types of subsidies and environmental gradients (e.g., temperature, canopy cover, and hydrology); and 6) the interaction of litter subsidies with anthropogenic disturbances. We conclude by highlighting several high‐priority research questions and providing suggestions for future research on the role of litter subsidies in freshwater ecosystems.
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Lethal effects of leaf leachate from the non-native invasive shrub Amur honeysuckle ( Lonicera maackii ) on a model aquatic organism ( Hyalella azteca )
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The invasive shrub Lonicera maackii (Amur honeysuckle) is a problematic species in the eastern United States and there is growing evidence that materials from this species have toxic effects on some organisms. We used a sequence of microcosm bioassays to assess the influence of L. maackii leaf leachate on the macroinvertebrate Hyalella azteca, which is a standard aquatic organism for toxicity assessment. In a laboratory setting, H. azteca were exposed to a leaf leachate dilution series (6.25%, 12.5%, 25%, 50%, 100%) in 48-h toxicity tests. This was repeated throughout the growing season to assess the potential for changes in leaf toxicity due to phenology. Strong toxic effects were found when H. azteca was exposed to a L. maackii leachate from autumn (P < 0.05) and, in fact, all organisms died when exposed to any level of concentration in most trials. Mean percent survival also decreased significantly in all dilutions in the spring (P < 0.05 for all treatments); however, little toxicity was detected in growing season trials. These results suggest (a) strong toxic effects of L. maackii foliage on a model aquatic organism that (b) varies throughout the year, potentially in relationship to biochemical changes associated with phenology.
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Secondary invasion: When invasion success is contingent on other invaders altering the properties of recipient ecosystems
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Positive interactions between exotic species may increase ecosystem-level impacts and potentially facilitate the entry and spread of other exotic species. Invader-facilitated invasion success—”secondary invasion”—is a key conceptual aspect of the well-known invasional meltdown hypothesis, but remains poorly defined and empirically underexplored. Drawing from heuristic models and published empirical studies, we explore this form of “secondary invasion” and discuss the phenomenon within the recognized conceptual framework of the determinants of invasion success. The term “secondary invasion” has been used haphazardly in the literature to refer to multiple invasion phenomena, most of which have other more accepted titles. Our usage of the term secondary invasion is akin to “invader-facilitated invasion,” which we define as the phenomenon in which the invasion success of one exotic species is contingent on the presence, influence, and impacts of one or more other exotic species. We present case studies of secondary invasion whereby primary invaders facilitate the entry or establishment of exotic species into communities where they were previously excluded from becoming invasive. Our synthesis, discussion, and conceptual framework of this type of secondary invasion provides a useful reference to better explain how invasive species can alter key properties of recipient ecosystems that can ultimately determine the invasion success of other species. This study increases our appreciation for complex interactions following invasion and highlights the impacts of invasive species themselves as possible determinants of invasion success. We anticipate that highlighting “secondary invasion” in this way will enable studies reporting similar phenomena to be identified and linked through consistent terminology.
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Article
  • Apr 2017
Human modification of landscapes has substantially altered the quality and quantity of terrestrial subsidies to freshwater ecosystems. The same modifications frequently lead to addition of chemical contaminants to freshwater environments. Both types of environmental change can alter the abundance of species and can lead to ecological interactions that affect entire communities. We examined how variation of tree litter inputs interacts with inputs of road salt deicers, which are an increasingly common contaminant in northern latitudes. Based on studies of the effects of each factor in isolation, we hypothesized that elevated Cl⁻ levels would reduce copepod densities, increase algal abundance, and subsequently increase salt-tolerant consumer densities and biomass. We also hypothesized that these effects would be most pronounced in the presence of highly soluble leaf litter (e.g., Acer rubrum). We constructed experimental freshwater ponds containing assemblages of phytoplankton, periphyton, zooplankton, Physa acuta snails, and 2 species of tadpoles (Lithobates sylvaticus and Anaxyrus americanus). We used a fully factorial design, manipulating leaf litter (none, A. rubrum, or Quercus velutina) and Cl⁻ concentration (114, 220, 314, and 867 mg Cl/L). Road salt at the 3 lower concentrations had few significant effects. The highest Cl⁻ concentration reduced copepod densities and increased phytoplankton concentrations, but only in the presence of maple litter. We also observed increased rotifer densities in the highest Cl⁻ concentration, but only in the presence of either litter species. Our results indicate that road salt contamination can have significant effects on wetland community composition at relatively high concentrations, but these effects depend on the chemistry of allochthonous inputs.
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Genetic and biochemical effects induced by iron ore, Fe and Mn exposure in tadpoles of the bullfrog Lithobates catesbeianus
Article
  • Feb 2016
For decades, the extraction of minerals has intensified in order to meet the demand of industry. Iron ore deposits are important sources of metals, such as iron (Fe) and manganese (Mn). The particulate ores can be dispersed during extraction, transport and storage, with potential to induce biological impacts. Amphibians are very sensitive to environmental stressors. Therefore, the present study aimed to assess the effects of iron ore, Fe and Mn exposure during the metamorphosis of Lithobates catesbeianus. Endpoints analyzed included morphological (biometrical and developmental analyses), whole body Fe and Mn concentration in, plasma ferritin concentration, erythrocyte DNA damage (measured through comet assay and micronucleus test) and liver activity of enzymes involved in oxidative status [glutathione S-transferase (GST) and catalase (CAT)]. Tadpoles were kept under control condition (no contaminant addition) or exposed to iron ore (3.79 mg/L as fine particulate matter); Fe (nominal concentration: 0.51 mg/L Fe as C10H12FeN2NaO8; Fe-EDTA); and Mn (nominal concentration: 5.23 mg/L Mn as 4H2O.MnCl2) for 30 days. Virtually, no mortality was observed, except for one tadpole found dead in the iron ore treatment. However, tadpoles exposed to iron ore had longer tail than those kept under control conditions while tadpoles exposed to manganese chloride showed higher body length than control ones. Exposure to Fe and Mn induced a delay in tadpole metamorphosis, especially when these metals are presented not as a mixture (iron ore). Tadpoles exposed to iron ore had increased whole body Fe and Mn while those exposed to Fe and Mn accumulated each metal individually. Tadpoles exposed to any of the contaminants tested showed a significant increase in erythrocyte DNA damage and frequency of micronuclei. In addition, they showed higher liver GST activity respect with those kept under control conditions. Plasma ferritin concentration and liver CAT activity were higher only in tadpoles exposed to iron ore. These findings indicated that tadpoles accumulated Fe and Mn at the whole body level after exposure to the single metals or to their mixture as iron ore. In addition, they indicate that Fe and Mn accumulation can induce oxidative stress with consequent significant developmental, genotoxic and biochemical effects in L. catesbeianus tadpoles.
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