Outbreak of an undetected invasive species triggered by a climate anomaly

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecosphere 7 (2016): e01628, doi:10.1002/ecs2.1628.When an invasive species appears at a new location, we typically have no knowledge of the population dynamics leading up to that moment. Is the establishment of invasive propagules closely followed by the appearance of the population? Or alternatively, was there an established low-density population that was released from a constraint and crossed the detection threshold? The early stages of the invasion process are a critical gap in our knowledge, yet vitally important for the detection and management of invasions. Here, we present multiple lines of evidence supporting the lag scenario for an invasive species outbreak. The invasive predatory zooplankton, spiny water flea (Bythotrephes longimanus), was detected in Lake Mendota, Wisconsin (USA), in summer of 2009 and rapidly reached and sustained exceptionally high densities. To evaluate whether Bythotrephes' outbreak immediately followed introduction or erupted from an established low-density population, we constructed a population model of Bythotrephes in Lake Mendota. In the model, Bythotrephes persisted indefinitely at low levels until favorable thermal conditions in 2009, the coolest July since at least 1895, allowed it to erupt to high densities and establish a large egg bank in the lake sediments. The egg bank stabilized the population in the high-density state despite a return to nonfavorable thermal conditions, which is further supported by demographic data suggesting a constant contribution from the egg bank during the year. The prolonged lag scenario is corroborated by the detection of two individual Bythotrephes in pre-2009 archived samples, and the detection of Bythotrephes spines in lake sediment core layers dating back to 1994 (±5 yr). Together, our results suggest that Bythotrephes persisted for at least a decade below the detection limit, until optimal thermal conditions triggered a population outbreak. This work highlights the potential for environmental conditions to trigger invasive species outbreaks from low-density populations.NSF North Temperate Lakes Long-Term Ecological Research Program Grant Numbers: DEB-0217533, DEB-1440297; Wisconsin Department of Natural Resource

Forecasting the distribution of the invasive round goby (Neogobius melanostomus) in Wisconsin tributaries to Lake Michigan

Abstract: The Laurentian Great Lakes host more than 180 non-native species, including several that have resulted in major economic and ecological effects. This list includes the round goby (Neogobius melanostomus), an aggressive, benthic Ponto-Caspian fish that has established large populations in coastal Great Lakes habitats. Here, we document the inland dispersal of round gobies into Wisconsin tributaries of Lake Michigan. Round gobies were detected in 26 of 73 streams (36%) and found >10 km upstream of Lake Michigan in nine watersheds. Round goby presence-absence was modeled using landscape-scale data from these invaded streams. We forecasted the future spread of round goby within Wisconsin's Lake Michigan basin using our best model (80% accuracy), which included watershed area, stream gradient, and watershed slope as predictors. Round gobies were predicted to invade 1369 km of stream habitat up to the first stream barrier, and 8878 km of stream was identified as suitable looking beyond barriers at the broader Lake Michigan watershed (Wisconsin only). Our results depict the Great Lakes as a springboard for invasive species to disperse into inland ecosystems and, because round gobies are not usually reported in small streams in their native range, emphasize the utility of data from invaded regions when forecasting invasive species distributions. Résumé : Les Grands Lacs Laurentiens contiennent >180 espèces non indigènes dont plusieurs ont eu des effets économi-ques et écologiques importants. Cette liste comprend le gobie à taches noires (Neogobius melanostomus), un poisson agressif d'origine ponto-caspienne, qui a formé de grandes populations dans les habitats côtiers des Grands Lacs. Nous apportons des informations sur la dispersion vers l'intérieur des gobies à taches noires dans les tributaires du lac Michigan au Wisconsin. Les gobies à taches noires se retrouvent dans 26 de 73 cours d'eau (36 %) et à >10 km en amont du lac Michigan dans neuf bassins versants. Nous avons modélisé la présence-absence des gobies à taches noires à l'aide de données à l'échelle du paysage provenant des cours d'eau envahis. Nous prédisons la dispersion future du gobie à taches noires dans le bassin versant du lac Michigan au Wisconsin à l'aide de notre meilleur (80 % d'exactitude) modèle qui inclut la surface du bassin versant, le gradient du cours d'eau et la pente du bassin comme variables prédictives. Notre pré-diction est que les gobies à taches noires vont envahir 1369 km d'habitat lotique jusqu'à la première barrière dans les cours d'eau; de plus, 8878 km de cours d'eau au-delà des barrières paraissent des habitats convenables dans le bassin élargi du lac Michigan (dans le seul Wisconsin). Nos résultats décrivent les Grands Lacs comme des tremplins pour les espèces envahissantes vers les écosystèmes de l'intérieur; comme les gobies à taches noires ne se retrouvent pas générale-ment dans les petits cours d'eau dans leur aire de répartition indigène, nos résultats soulignent l'utilité de données provenant des régions envahies pour la prédiction des répartitions des espèces envahissantes. [Traduit par la Rédaction

Historical and contemporary trophic niche partitioning among Laurentian Great Lakes coregonines

Abstract. Anthropogenic activities have significantly altered freshwater fish communities. Extirpations of deepwater coregonines (Coregonus spp.), a diverse group of fish species, have left vast areas of the Laurentian Great Lakes devoid of a deepwater fish community. Currently, fisheries managers are considering restoring populations by reintroducing deepwater coregonines from Lake Superior and Lake Nipigon. However, little is known about the historical ecology of deepwater coregonines, and species characterization has proved difficult. We used stable isotope analysis of museum-preserved and contemporary specimens to investigate if (1) coregonine species historically occupied distinct niches and (2) the pattern of trophic niche partitioning has changed over the last century. Across all lakes, individual species occupied distinct trophic niches, confirming that these species were ecologically distinct. Understanding trophic niche partitioning helps resolve uncertainty about distinctness of species within and across lakes and may provide a better ecological basis for rehabilitation of Great Lakes food webs and ecosystems

Taking the trophic bypass : aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web

Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems

Taking the trophic bypass: aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web

Abstract. Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems

Fish community composition and habitat use in the Eg-Uur River System,

Abstract Mongolian rivers and their fi sh communities have suffered severe impacts from anthropogenic activities. However, the remoteness of some systems has allowed for the conservation of unique fi sh faunas, including robust populations of Hucho taimen. Conservation of H. taimen requires understanding the composition and ecology of other fi shes in the community. Using multiple sampling techniques, direct observation, and existing literature, we assessed the composition, relative abundance, and ecological attributes of fi shes in the Eg-Uur watershed (Selenge basin). We collected 6 of 12 species known in the watershed. Phoxinus cf. phoxinus and Lota lota were the most and least abundant species, respectively. We failed to detect H. taimen, indicating low abundance or unknown habitat requirements for juveniles. We compared the effectiveness of different sampling techniques (with electrofi shing producing the highest species richness), constructed length-weight relationships for four species, and identifi ed ecological attributes (i.e., trophic guild, preferred habitat) for resident fi shes

Fish community composition and habitat use in the Eg-Uur River System,

Abstract Mongolian rivers and their fi sh communities have suffered severe impacts from anthropogenic activities. However, the remoteness of some systems has allowed for the conservation of unique fi sh faunas, including robust populations of Hucho taimen. Conservation of H. taimen requires understanding the composition and ecology of other fi shes in the community. Using multiple sampling techniques, direct observation, and existing literature, we assessed the composition, relative abundance, and ecological attributes of fi shes in the Eg-Uur watershed (Selenge basin). We collected 6 of 12 species known in the watershed. Phoxinus cf. phoxinus and Lota lota were the most and least abundant species, respectively. We failed to detect H. taimen, indicating low abundance or unknown habitat requirements for juveniles. We compared the effectiveness of different sampling techniques (with electrofi shing producing the highest species richness), constructed length-weight relationships for four species, and identifi ed ecological attributes (i.e., trophic guild, preferred habitat) for resident fi shes

Shorter Food Chain Length in Ancient Lakes: Evidence from a Global Synthesis

Food webs may be affected by evolutionary processes, and effective evolutionary time ultimately affects the probability of species evolving to fill the niche space. Thus, ecosystem history may set important evolutionary constraints on community composition and food web structure. Food chain length (FCL) has long been recognized as a fundamental ecosystem attribute. We examined historical effects on FCL in large lakes spanning >6 orders of magnitude in age. We found that food chains in the world’s ancient lakes (n = 8) were significantly shorter than in recently formed lakes (n = 10) and reservoirs (n = 3), despite the fact that ancient lakes harbored much higher species richness, including many endemic species. One potential factor leading to shorter FCL in ancient lakes is an increasing diversity of trophic omnivores and herbivores. Speciation could simply broaden the number of species within a trophic group, particularly at lower trophic levels and could also lead to a greater degree of trophic omnivory. Our results highlight a counter-intuitive and poorly-understood role of evolutionary history in shaping key food web properties such as FCL