29 Publikation(en)

Boom-bust dynamics in biological invasions: towards an improved application of the concept

Ecology Letters 20(10)

Strayer DL, D'Antonio CM, Essl F, Fowler MS, Geist J, Hilt S, Jarić I, Jöhnk K, Jones CG, Lambin X, Latzka AW, Pergl J, Pyšek P, Robertson P, von Schmalensee M, Stefansson RA, Wright J, Jeschke JM

Wiley-Blackwell | 2017-08-17

Erschienen in: Ecology Letters 20(10): 1337-1350

Boom-bust dynamics - the rise of a population to outbreak levels, followed by a dramatic decline - have been associated with biological invasions and offered as a reason not to manage troublesome invaders. However, boom-bust dynamics rarely have been critically defined, analyzed, or interpreted. Here, we define boom-bust dynamics and provide specific suggestions for improving the application of the boom-bust concept. Boom-bust dynamics can arise from many causes, some closely associated with invasions, but others occurring across a wide range of ecological settings, especially when environmental conditions are changing rapidly. As a result, it is difficult to infer cause or predict future trajectories merely by observing the dynamic. We use tests with simulated data to show that a common metric for detecting and describing boom-bust dynamics, decline from an observed peak to a subsequent trough, tends to severely overestimate the frequency and severity of busts, and should be used cautiously if at all. We review and test other metrics that are better suited to describe boom-bust dynamics. Understanding the frequency and importance of boom-bust dynamics requires empirical studies of large, representative, long-term data sets that use clear definitions of boom-bust, appropriate analytical methods, and careful interpretations.

Thema: alien species; biological invasions; concepts; exotic species; invasive species; long-term; management; non-native species; population collapse; population crash; population dynamics; reckless invaders; systematic review

Assessing patterns in introduction pathways of alien species by linking major invasion data bases

Journal of Applied Ecology 54(2)

Saul W-C, Roy HE, Booy O, Carnevali L, Chen H-J, Genovesi P, Harrower CA, Hulme PE, Pagad S, Pergl J, Jeschke JM

Wiley-Blackwell | 2017-03-17

Erschienen in: Journal of Applied Ecology 54(2): 657–669 ...

Summary: 1. Preventing the arrival of invasive alien species (IAS) is a major priority in managing biological invasions. However, information on introduction pathways is currently scattered across many data bases that often use different categorisations to describe similar pathways. This hampers the identification and prioritisation of pathways to meet the main targets of recent environmental policies. 2. Therefore, we integrate pathway information from two major IAS data bases, IUCN's Global Invasive Species Database (GISD) and the DAISIE European Invasive Alien Species Gateway, applying the new standard categorisation scheme recently adopted by the Convention on Biological Diversity (CBD). We describe the process of mapping pathways from the individual data bases to the CBD scheme and provide, for the first time, detailed descriptions of the standard pathway categories. The combined data set includes pathway information for 8323 species across major taxonomic groups (plants, vertebrates, invertebrates, algae, fungi, other) and environments (terrestrial, freshwater, marine). 3. We analyse the data for major patterns in the introduction pathways, highlighting that the specific research question and context determines whether the combined or an individual data set is the better information source for such analyses. While the combined data set provides an improved basis for direction-setting in invasion management policies on the global level, individual data sets often better reflect regional idiosyncrasies. The combined data set should thus be considered in addition to, rather than replacing, existing individual data sets. 4. Pathway patterns derived from the combined and individual data sets show that the intentional pathways ‘Escape’ and ‘Release’ are most important for plants and vertebrates, while for invertebrates, algae, fungi and micro-organisms unintentional transport pathways prevail. Differences in pathway proportions among marine, freshwater and terrestrial environments are much less pronounced. The results also show that IAS with highest impacts in Europe are on average associated with a greater number of pathways than other alien species and are more frequently introduced both intentionally and unintentionally. 5. Synthesis and applications. Linking data bases on invasive alien species by harmonising and consolidating their pathway information is essential to turn dispersed data into useful knowledge. The standard pathway categorisation scheme recently adopted by the Convention on Biological Diversity may be crucial to facilitate this process. Our study demonstrates the value of integrating major invasion data bases to help managers and policymakers reach robust conclusions about patterns in introduction pathways and thus aid effective prevention and prioritisation in invasion management.

Thema: biosecurity, escape, introduction pathways, invasion management, invasive non-native species, prevention, prioritisation, release, standard pathway categorisation, transport

No saturation in the accumulation of alien species worldwide

Nature Communications 8

Seebens, H.; Blackburn, T.M.; Dyer, E.E.; Genovesi, P.; Hulme, P.E.; Jeschke, J.M.; Pagad, S.; Pyšek, P.; Winter, M.; Arianoutsou, M.; Bacher, S.; Blasius, B.; Brundu, G.; Capinha, C.; Celesti-Grapow, L.; Dawson, W.; Dullinger, S.; Fuentes, N.; Jäger

Nature Pub. Group | 2017-02-15

Erschienen in: Nature Communications 8: 14435

Although research on human-mediated exchanges of species has substantially intensified during the last centuries, we know surprisingly little about temporal dynamics of alien species accumulations across regions and taxa. Using a novel database of 45,813 first records of 16,926 established alien species, we show that the annual rate of first records worldwide has increased during the last 200 years, with 37% of all first records reported most recently (1970-2014). Inter-continental and inter-taxonomic variation can be largely attributed to the diaspora of European settlers in the nineteenth century and to the acceleration in trade in the twentieth century. For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time. This highlights that past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.

Threat-dependent traits of endangered frogs

Biological Conservation 206

Ruland F, Jeschke JM

Wiley-Blackwell | 2017-02

Erschienen in: Biological Conservation 206: 310-313 ...

Numerous studies have investigated life-history and other traits of endangered species for conservation purposes. These studies typically look for universal traits independently of the reasons why species are threatened. The usefulness of such analyses is limited if the traits are actually threat-dependent, but whether that is the case is currently unknown. We investigated if two traits of anurans – snout-vent length and habitat breadth – are threat-dependent, using the threats human consumption and pet trade as case examples. Analysing a unique global dataset (1041 species with data on snout-vent length and 4103 species with data on habitat breadth), we show that the traits of endangered anurans are strongly threat-dependent. For instance, while snout-vent length is similar between threatened and non-threatened frogs when not discriminating between threats, distinct differences become apparent when considering the reasons why the species are threatened: frogs threatened by human consumption have large body sizes, whereas those threatened by the pet trade are small. Thus at least for frogs, searching for universal traits of endangered species independently of the reasons why they are threatened does not seem to be rewarding. Instead, we need to better understand the relationship between the traits of endangered species and the reasons why they are threatened. This will help better predicting which species will become more critically endangered (or can recover) if certain threats will increase (or decrease) in their magnitude in the future.

Thema: Amphibians; Conservation; Habitat breadth; IUCN Red List; Pet trade; Snout-vent length

Invasion biology: specific problems and possible solutions

Trends in Ecology & Evolution 32(1)

Courchamp, F.; Fournier, A.; Bellard, C.; Bertelsmeier, C.; Bonnaud, E.; Jeschke, J.M.; Russell, J.C.

Cell Press | 2017-01

Erschienen in: Trends in Ecology & Evolution 32(1): 13-22 ...

Biological invasions have been unambiguously shown to be one of the major global causes of biodiversity loss. Despite the magnitude of this threat and recent scientific advances, this field remains a regular target of criticism - from outright deniers of the threat to scientists questioning the utility of the discipline. This unique situation, combining internal strife and an unaware society, greatly hinders the progress of invasion biology. It is crucial to identify the specificities of this discipline that lead to such difficulties. We outline here 24 specificities and problems of this discipline and categorize them into four groups: understanding, alerting, supporting, and implementing the issues associated with invasive alien species, and we offer solutions to tackle these problems and push the field forward.

Thema: biological invasions; citizen involvement; decision making; engaging with the public; science communication; science–society interface

Warming can enhance invasion success through asymmetries in energetic performance

Journal of Animal Ecology 85(2)

Penk MR, Jeschke JM, Minchin D, Donohue I

Wiley-Blackwell | 2016-03

Erschienen in: Journal of Animal Ecology 85(2): 419-426 ...

Both climate warming and biological invasions are prominent drivers of global environmental change and it is important to determine how they interact. However, beyond tolerance and reproductive thresholds, little is known about temperature dependence of invaders' performance, particularly in the light of competitive attributes of functionally similar native species. We used experimentally derived energy budgets and field temperature data to determine whether anticipated warming will asymmetrically affect the energy budgets of the globally invasive Ponto-Caspian mysid crustacean Hemimysis anomala and a functionally similar native competitor (Mysis salemaai) whose range is currently being invaded. In contrast to M. salemaai, which maintains a constant feeding rate with temperature leading to diminishing energy assimilation, we found that H. anomala increases its feeding rate with temperature in parallel with growing metabolic demand. This enabled the invader to maintain high energy assimilation rates, conferring substantially higher scope for growth compared to the native analogue at spring-to-autumn temperatures. Anticipated warming will likely exacerbate this energetic asymmetry and remove the winter overlap, which, given the seasonal limitation of mutually preferred prey, appears to underpin coexistence of the two species. These results indicate that temperature-dependent asymmetries in scope for growth between invaders and native analogues comprise an important mechanism determining invasion success under warming climates. They also highlight the importance of considering relevant spectra of ecological contexts in predicting successful invaders and their impacts under warming scenarios.

Thema: Hemimysis anomala; Mysis salemaai; assimilation; climate change; competition; energy budget; feeding rate; invasive species; lake; respiration

Global patterns in threats to vertebrates by biological invasions

Proceedings of the Royal Society B 283(1823)

Bellard C, Genovesi P, Jeschke JM

Royal Society of London | 2016-01-27

Erschienen in: Proceedings of the Royal Society B 283(1823)

Biological invasions as drivers of biodiversity loss have recently been challenged. Fundamentally, we must know where species that are threatened by invasive alien species (IAS) live, and the degree to which they are threatened. We report the first study linking 1372 vertebrates threatened by more than 200 IAS from the completely revised Global Invasive Species Database. New maps of the vulnerability of threatened vertebrates to IAS permit assessments of whether IAS have a major influence on biodiversity, and if so, which taxonomic groups are threatened and where they are threatened. We found that centres of IAS-threatened vertebrates are concentrated in the Americas, India, Indonesia, Australia and New Zealand. The areas in which IAS-threatened species are located do not fully match the current hotspots of invasions, or the current hotspots of threatened species. The relative importance of biological invasions as drivers of biodiversity loss clearly varies across regions and taxa, and changes over time, with mammals from India, Indonesia, Australia and Europe are increasingly being threatened by IAS. The chytrid fungus primarily threatens amphibians, whereas invasive mammals primarily threaten other vertebrates. The differences in IAS threats between regions and taxa can help efficiently target IAS, which is essential for achieving the Strategic Plan 2020 of the Convention on Biological Diversity.

Thema: alien species; biological invasions; non-native species; threatened species; vertebrates

Intraspecific trait variation is correlated with establishment success of alien mammals

The American Naturalist 185(6)

González-Suárez, M.; Bacher, S.; Jeschke, J.M.

The University of Chicago Press | 2015-03-30

Erschienen in: The American Naturalist, Vol. 185, No. 6 (June 2015), pp. 737-746

Many studies have aimed to identify common predictors of successful introductions of alien species, but the search has had limited success, particularly for animals. Past research focused primarily on mean trait values, even though genetic and phenotypic variation has been shown to play a role in establishment success in plants and some animals (mostly invertebrates). Using a global database describing 511 introduction events representing 97 mammalian species, we show that intraspecific variation in morphological traits is associated with establishment success, even when controlling for the positive effect of propagule pressure. In particular, greater establishment success is associated with more variation in adult body size but, surprisingly, less variation in neonate body size, potentially reflecting distinct trade-offs and constraints that influence population dynamics differently. We find no mean trait descriptors associated with establishment success, although species occupying wider native distribution ranges (which likely have larger niches) are more successful. Our results emphasize the importance of explicitly considering intraspecific variation to predict establishment success in animal species and generally to understand population dynamics. This understanding might improve management of alien species and increase the success of intentional releases, for example, for biocontrol or reintroductions.

Thema: alien species, biological invasions, coefficient of variation, invasive species, plasticity hypothesis, trait variation

Eco-evolutionary experience in novel species interactions

Ecology Letters 18(3)

Wolf-Christian Saul, Jonathan M. Jeschke

Wiley-Blackwell | 2015-01-27

Erschienen in: Ecology Letters, Volume 18, Issue 3, pages 236–245, March 2015

A better understanding of how ecological novelty influences interactions in new combinations of species is key for predicting interaction outcomes, and can help focus conservation and management efforts on preventing the introduction of novel organisms or species (including invasive species, GMOs, synthetic organisms, resurrected species and emerging pathogens) that seem particularly ‘risky’ for resident species. Here, we consider the implications of different degrees of eco-evolutionary experience of interacting resident and non-resident species, define four qualitative risk categories for estimating the probability of successful establishment and impact of novel species and discuss how the effects of novelty change over time. Focusing then on novel predator–prey interactions, we argue that novelty entails density-dependent advantages for non-resident species, with their largest effects often being at low prey densities. This is illustrated by a comparison of predator functional responses and prey predation risk curves between novel species and ecologically similar resident species, and raises important issues for the conservation of endangered resident prey species.

Thema: Alien species; Anthropocene; ecological novelty; ecological similarity; introduced species; invasibility; invasiveness; management; naïveté ;teady-state satiation equation

General hypotheses in invasion ecology

Diversity and Distributions 20(11)

Jonathan M. Jeschke

Wiley-Blackwell | 2014-09-13

Erschienen in: Diversity and Distributions, (Diversity Distrib.) (2014) 20, 1229–1234

A Unified Classification of Alien Species Based on the Magnitude of their Environmental Impacts

PLOS Biology 12(5)

Tim M. Blackburn, Franz Essl, Thomas Evans, Philip E. Hulme, Jonathan M. Jeschke, Ingolf Kühn, Sabrina Kumschick, Zuzana Marková, Agata Mrugała, Wolfgang Nentwig, Jan Pergl, Petr Pyšek, Wolfgang Rabitsch, Anthony Ricciardi, David M. Richardson, Agnieszka Sendek, Montserrat Vilà, John R. U. Wilson, Marten Winter, Piero Genovesi, Sven Bacher

Public Library of Science | 2014-05-06

Erschienen in: PLOS Biology, Volume 12, Issue 5, e1001850 (May 2014) ...

Species moved by human activities beyond the limits of their native geographic ranges into areas in which they do not naturally occur (termed aliens) can cause a broad range of significant changes to recipient ecosystems; however, their impacts vary greatly across species and the ecosystems into which they are introduced. There is therefore a critical need for a standardised method to evaluate, compare, and eventually predict the magnitudes of these different impacts. Here, we propose a straightforward system for classifying alien species according to the magnitude of their environmental impacts, based on the mechanisms of impact used to code species in the International Union for Conservation of Nature (IUCN) Global Invasive Species Database, which are presented here for the first time. The classification system uses five semi-quantitative scenarios describing impacts under each mechanism to assign species to different levels of impact—ranging from Minimal to Massive—with assignment corresponding to the highest level of deleterious impact associated with any of the mechanisms. The scheme also includes categories for species that are Not Evaluated, have No Alien Population, or are Data Deficient, and a method for assigning uncertainty to all the classifications. We show how this classification system is applicable at different levels of ecological complexity and different spatial and temporal scales, and embraces existing impact metrics. In fact, the scheme is analogous to the already widely adopted and accepted Red List approach to categorising extinction risk, and so could conceivably be readily integrated with existing practices and policies in many regions.

Defining the Impact of Non-Native Species

Diversity Distrib. 20

Jeschke, J.M.; Bacher, S.; Blackburn, T.M.; Dick, J.T.A.; Essl, F.; Evans, T.; Gaertner, M.; Hulme, P.E.; Kühn, I.; Mrugała, A.; Pergl, J.; Pyšek, P.; Rabitsch, W.; Ricciardi, A.; Richardson, D.M.; Sendek, A.; Vilà, M.; Winter, M.; Kumschick, S.

Wiley Periodicals, Inc. | 2014-04-29

Erschienen in: Conservation Biology, Volume 28, Issue 5, pages 1188–1194, October 2014

Non-native species cause changes in the ecosystems to which they are introduced. These changes, or some of them, are usually termed impacts; they can be manifold and potentially damaging to ecosystems and biodiversity. However, the impacts of most non-native species are poorly understood, and a synthesis of available information is being hindered because authors often do not clearly define impact. We argue that explicitly defining the impact of non-native species will promote progress toward a better understanding of the implications of changes to biodiversity and ecosystems caused by non-native species; help disentangle which aspects of scientific debates about non-native species are due to disparate definitions and which represent true scientific discord; and improve communication between scientists from different research disciplines and between scientists, managers, and policy makers. For these reasons and based on examples from the literature, we devised seven key questions that fall into 4 categories: directionality, classification and measurement, ecological or socio-economic changes, and scale. These questions should help in formulating clear and practical definitions of impact to suit specific scientific, stakeholder, or legislative contexts.

Thema: biological invasions; definitions; ecological and socio-economic impacts; exotic species;human perception; invasion biology; invasive alien species

Novel organisms: comparing invasive species, GMOs, and emerging pathogens

AMBIO 42(5)

Jeschke, J.M.; Keesing, F.; Ostfeld, R.S.

Springer Science+Business Media | 2013-03-03

Erschienen in: AMBIO, Volume 42, Issue 5, pp 541-548 (September 2013) ...

Invasive species, range-expanding species, genetically modified organisms (GMOs), synthetic organisms, and emerging pathogens increasingly affect the human environment. We propose a framework that allows comparison of consecutive stages that such novel organisms go through. The framework provides a common terminology for novel organisms, facilitating knowledge exchange among researchers, managers, and policy makers that work on, or have to make effective decisions about, novel organisms. The framework also indicates that knowledge about the causes and consequences of stage transitions for the better studied novel organisms, such as invasive species, can be transferred to more poorly studied ones, such as GMOs and emerging pathogens. Finally, the framework advances understanding of how climate change can affect the establishment, spread, and impacts of novel organisms, and how biodiversity affects, and is affected by, novel organisms.

Thema: Biological invasions, Ecological novelty, Emerging diseases, Genetically modified organisms, Range-expanding species, Synthetic organisms

Taxonomic bias and lack of cross-taxonomic studies in invasion biology

Frontiers in Ecology and the Environment 10(7)

Jonathan M Jeschke, Lorena Gómez Aparicio, Sylvia Haider, Tina Heger, Christopher J Lortie, Petr Pyšek, David L Strayer

Ecological Society of America | 2012-09

Erschienen in: Frontiers in Ecology and the Environment, September, Vol. 10, No. 7 : 349-350

Support for major hypotheses in invasion biology is uneven and declining

NeoBiota 14

Jonathan M. Jeschke, Lorena Gómez Aparicio, Sylvia Haider, Tina Heger, Christopher J. Lortie, Petr Pyšek, David L. Strayer

Pensoft | 2012-08-22

Erschienen in: NeoBiota 14: 1-20 (22 Aug 2012) ...

Several major hypotheses have been proposed to explain and predict biological invasions, but the general applicability of these hypotheses is largely unknown, as most of them have not been evaluated using a standard approach across taxonomic groups and habitats. We offer such an evaluation for six selected leading hypotheses. Our global literature review reveals that those hypotheses that consider interactions of exotic invaders with their new environment (invasional meltdown, novel weapons, enemy release) are better supported by empirical evidence than other hypotheses (biotic resistance, island susceptibility, tens rule). We also show that empirical support for the six hypotheses has declined over time, and that support differs among taxonomic groups and habitats. Our results have implications for basic and applied research, policy making, and invasive species management, as their effectiveness depends on sound hypotheses.

Thema: Biological invasions, biotic resistance hypothesis, decline effect, enemy release hypothesis, invasional meltdown hypothesis, island susceptibility hypothesis, novel weapons hypothesis, tens rule

Do biodiversity and human impact influence the introduction or establishment of alien mammals?

Oikos 120(1)

Jonathan M. Jeschke, Piero Genovesi

Wiley-Blackwell | 2010-06-25

Erschienen in: Oikos, Volume 120, Issue 1, pages 57–64, January 2011 ...

What determines the number of alien species in a given region? ‘Native biodiversity’ and ‘human impact’ are typical answers to this question. Indeed, studies comparing different regions have frequently found positive relationships between number of alien species and measures of both native biodiversity (e.g. the number of native species) and human impact (e.g. human population). These relationships are typically explained by biotic acceptance or resistance, i.e. by influence of native biodiversity and human impact on the second step of the invasion process, establishment. The first step of the invasion process, introduction, has often been ignored. Here we investigate whether relationships between number of alien mammals and native biodiversity or human impact in 43 European countries are mainly shaped by differences in number of introduced mammals or establishment success. Our results suggest that correlation between number of native and established mammals is spurious, as it is simply explainable by the fact that both quantities are linked to country area. We also demonstrate that countries with higher human impact host more alien mammals than other countries because they received more introductions than other countries. Differences in number of alien mammals cannot be explained by differences in establishment success. Our findings highlight importance of human activities and question, at least for mammals in Europe, importance of biotic acceptance and resistance.

Are invaders different? A conceptual framework of comparative approaches for assessing determinants of invasiveness

Ecology Letters 13(8)

Mark Van Kleunen, Wayne Dawson, Daniel Schlaepfer, Jonathan M. Jeschke, Markus Fischer

Wiley | 2010-06-23

Erschienen in: Ecology Letters, Volume 13, Issue 8, pages 947–958 (August 2010) ...

What determines invasiveness of alien organisms is among the most interesting and urgent questions in ecology. In attempts to answer this question, researchers compare invasive alien species either to native species or to non-invasive alien species, and this is done in either the introduced or native ranges. However, inferences that can be drawn from these comparisons differ considerably, and failure to recognize this could hamper the search for determinants of invasiveness. To increase awareness about this issue, we present a framework of the various comparisons that can be used to test for determinants of invasiveness, and the specific questions each comparison can address. Moreover, we discuss how different comparisons complement each other, and therefore should be used in concert. For progress in invasion biology, it is crucial to realize that different comparisons address different biological questions and that some questions can only be answered unambiguously by combining them.

Thema: Biological invasion; comparative studies; enemy release; evolution; exotic species; invasiveness; native species; non-indigenous species; traits

The roles of body size and phylogeny in fast and slow life histories

Evolutionary Ecology 23(6)

Jeschke, J.M.; Kokko, H.

Springer Netherlands | 2008-08-05

Erschienen in: Evolutionary Ecology, Volume 23, Issue 6, pp 867-878 (November 2009) ...

Species’ life histories are often classified on a continuum from ‘‘fast’’ to ‘‘slow’’, yet there is no consistently used definition of this continuum. For example, some researchers include body mass as one of the traits defining the continuum, others factor it out by analysing body-mass residuals, a third group performs both of these analyses and uses the terms ‘‘fast’’ and ‘‘slow’’ in both ways, while still others do not mention body mass at all. Our analysis of European and North American freshwater fish, mammals, and birds (N = 2,288 species) shows the fundamental differences between life-history patterns of raw data and of body-mass residuals. Specifically, in fish and mammals, the number of traits defining the continuum decreases if body-mass residuals are analysed. In birds, the continuum is defined by a different set of traits if body mass is factored out. Our study also exposes important dissimilarities among the three taxonomic groups analysed. For example, while mammals and birds with a ‘‘slow’’ life history have a low fecundity, the opposite is true for fish. We conclude that our understanding of life histories will improve if differences between patterns of raw data and of body-mass residuals are acknowledged, as well as differences among taxonomic groups, instead of using the ‘‘fast–slow continuum’’ too indiscriminately for any covarying traits that appear to suit the idea.

Thema: Fast–slow continuum, K-strategists, Life-history patterns, Allometric scaling, r-strategists

Across islands and continents, mammals are more successful invaders than birds

Diversity and Distributions 14(6)

Jonathan M. Jeschke

Wiley-Blackwell | 2008-05-07

Erschienen in: Diversity and Distributions, Volume 14, Issue 6, pages 913–916 (November 2008) ...

Many invasive species cause ecological or economic damage, and the fraction of introduced species that become invasive is an important determinant of the overall costs caused by invaders. According to the widely quoted tens rule, about 10% of all introduced species establish themselves and about 10% of these established species become invasive. Global taxonomic differences in the fraction of species becoming invasive have not been described. In a global analysis of mammal and bird introductions, I show that both mammals and birds have a much higher invasion success than predicted by the tens rule, and that mammals have a significantly higher success than birds. Averaged across islands and continents, 79% of mammals and 50% of birds introduced have established themselves and 63% of mammals and 34% of birds established have become invasive. My analysis also does not support the hypothesis that islands are more susceptible to invaders than continents, as I did not find a significant relationship between invasion success and the size of the island or continent to which the species were introduced. The data set used in this study has a number of limitations, e.g. information on propagule pressure was not available at this global scale, so understanding the mechanisms behind the observed patterns has to be postponed to future studies.

Thema: Aves; biological invasions; exotic species; Mammalia; non-native species; resistance hypothesis; tens rule

Are threat status and invasion success two sides of the same coin?

Ecography 31(1)

Jonathan M. Jeschke, David L. Strayer

Wiley | 2008-01-31

Erschienen in: Ecography, Volume 31, Issue 1, pages 124–130 (February 2008) ...

Global change increases both the number of threatened species and the impacts of invasives. These two problems are sometimes assumed to be opposite sides of the same coin, with invasive species having the opposite characteristics of endangered species. However, the validity of this assumption has never been tested. We analysed 20 life-history and other traits of all European and North American freshwater fish and birds. For these 1813 species, we compared the determinants of invasion success and IUCN-threat status and found that traits favouring invasion are not simply the opposite of those that favour endangerment. The size and life history of species are correlated more strongly with threat status than invasiveness. On the other hand, association with humans is the best predictor of invasiveness but is not correlated with threat status. Thus, the rise of invaders is caused by different aspects of global change than the imperilment of endangered species.

Prey swarming: which predators become confused and why?

Animal Behaviour 74(3)

Jonathan M. Jeschke, Ralph Tollrian

Elsevier | 2007-08-16

Erschienen in: Animal Behaviour, Volume 74, Issue 3, Pages 387–393 ( September 2007) ...

When confronted with a swarm of their prey, many predators become confused and are less successful in their attacks. Despite the general notion that this confusion effect is a major reason for prey swarm formation, it is largely unknown how widespread it is and which predator or prey traits facilitate or impede it. We carried out experiments with four predator–prey systems: Aeshna and Chaoborus larvae, but not Libellula and Triturus larvae, became confused when confronted with high Daphnia densities. When combining this result with literature data, we found that predators became confused in 16 of the 25 predator–prey systems studied to date. Tactile predators appear to be generally susceptible, whereas visual predators are susceptible mainly when their prey is highly agile. This difference probably results from the superiority of the visual sensory system. However, while our study is an important step towards the mechanistic understanding of predator confusion, it also reveals how poor this understanding currently is.

Thema: Aeshna cyanea; attack efficiency; Chaoborus obscuripes; confusion effect; Daphnia magna; Daphnia obtusa; gregariousness; Libellula depressa; swarming effect; Triturus alpestris

When carnivores are “full and lazy“

Oecologia 152(2)

Jonathan M. Jeschke

Springer (Germany) | 2007-02-10

Erschienen in: Oecologia, Volume 152, Issue 2, pp 357-364 (May 2007) ...

Are animals usually hungry and busily looking for food, or do they often meet their energetic and other needs in the 24 h of a day? Focusing on carnivores, I provide evidence for the latter scenario. I develop a model that predicts the minimum food abundance at which a carnivore reaches satiation and is released from time constraints. Literature data from five invertebrate and vertebrate species suggest that food abundances experienced in the field often exceed this threshold. A comparison of energetic demands to kill rates also suggests that carnivores often reach satiation: for the 16 bird and mammal species analyzed, this frequency is 88% (average across species). Because pressure of time would likely lead to trade-offs in time allocation and thus to a nonsatiating food consumption, these results suggest that carnivores are often released from time constraints.

Thema: Energy-time budgets, Functional Responses, Kill rates, Principle of stringency, Time constraints

How partnerships end in guillemots Uria aalge: chance events, adaptive change, or forced divorce?

Animal Behaviour 74(3)

Jonathan M. Jeschke, Sarah Wanless, Michael P. Harris, Hanna Kokko

Oxford University Press | 2007-01-19

Erschienen in: Behavioral Ecology, Volume 18, Issue 2, pp 460-466 (2007)

Divorce in socially monogamous species can result from different mechanisms, for example, chance events, active desertion of the partner, or the intrusion of a third individual ousting the partner. We compared the predictions associated with such mechanisms with data from common guillemots (Uria aalge) breeding on the Isle of May, Scotland. The data cover the years 1982–2005 and show a yearly divorce rate of 10.2%. In most divorces (86%), one of the original partners moved to another breeding site, whereas the other bird stayed and bred with a new partner. On average, movers had a significantly lower breeding success after divorce, stayers were largely unaffected, whereas the incoming birds benefited significantly from the change. This pattern fits best the predictions of the “forced-divorce” hypothesis, suggesting that many divorces were caused by incoming birds rather than the original partners or chance events. Although we are unable to document the precise behavioral sequence that led to divorces, our interpretation is supported by observations of frequent fights over breeding-site ownership. Our data also indicate within-population diversity of divorce mechanisms: some divorces were apparently accidental, others desertion of partners and sites if the latter were of low quality. Our study finally illustrates that a negative correlation between breeding success and probability of divorce (which our data show) need not indicate the adaptiveness of divorce for the original partners. Because such a connection has often been made, adaptive divorce may in general be less common than usually assumed.

Thema: auks (Alcidae), common guillemots, common murres, forced divorce, pair-bonds, reunification rate

Understanding the long-term effects of species invasions

Trends in Ecology & Evolution 21(11)

David L. Strayer, Valerie T. Eviner, Jonathan M. Jeschke, Michael L. Pace

Cell Press | 2006-07-21

Erschienen in: Trends in Ecology & Evolution, Volume 21, Issue 11, November 2006, Pages 645–651 ...

We describe here the ecological and evolutionary processes that modulate the effects of invasive species over time, and argue that such processes are so widespread and important that ecologists should adopt a long-term perspective on the effects of invasive species. These processes (including evolution, shifts in species composition, accumulation of materials and interactions with abiotic variables) can increase, decrease, or qualitatively change the impacts of an invader through time. However, most studies of the effects of invasive species have been brief and lack a temporal context; 40% of recent studies did not even state the amount of time that had passed since the invasion. Ecologists need theory and empirical data to enable prediction, understanding and management of the acute and chronic effects of species invasions.

Determinants of vertebrate invasion success in Europe and North America

Global Change Biology 12(9)

Jonathan M. Jeschke, David L. Strayer

Wiley | 2006-07-17

Erschienen in: Global Change Biology, Volume 12, Issue 9, pages 1608–1619, September 2006 ...

Species that are frequently introduced to an exotic range have a high potential of becoming invasive. Besides propagule pressure, however, no other generally strong determinant of invasion success is known. Although evidence has accumulated that human affiliates (domesticates, pets, human commensals) also have high invasion success, existing studies do not distinguish whether this success can be completely explained by or is partly independent of propagule pressure. Here, we analyze both factors independently, propagule pressure and human affiliation. We also consider a third factor directly related to humans, hunting, and 17 traits on each species' population size and extent, diet, body size, and life history. Our dataset includes all 2362 freshwater fish, mammals, and birds native to Europe or North America. In contrast to most previous studies, we look at the complete invasion process consisting of (1) introduction, (2) establishment, and (3) spread. In this way, we not only consider which of the introduced species became invasive but also which species were introduced. Of the 20 factors tested, propagule pressure and human affiliation were the two strongest determinants of invasion success across all taxa and steps. This was true for multivariate analyses that account for intercorrelations among variables as well as univariate analyses, suggesting that human affiliation influenced invasion success independently of propagule pressure. Some factors affected the different steps of the invasion process antagonistically. For example, game species were much more likely to be introduced to an exotic continent than nonhunted species but tended to be less likely to establish themselves and spread. Such antagonistic effects show the importance of considering the complete invasion process.

Thema: aliens;establishment;exotics;introduction;invasion;naturalized species;nonindigenous species;nonnative species;sexual dimorphism;spread

Invasion success of vertebrates in Europe and North America


Jonathan M. Jeschke, David L. Strayer

PNAS | 2005-04-22 ...

Species become invasive if they (i) are introduced to a new range, (ii) establish themselves, and (iii) spread. To address the global problems caused by invasive species, several studies investigated steps ii and iii of this invasion process. However, only one previous study looked at step i and examined the proportion of species that have been introduced beyond their native range. We extend this research by investigating all three steps for all freshwater fish, mammals, and birds native to Europe or North America. A higher proportion of European species entered North America than vice versa. However, the introduction rate from Europe to North America peaked in the late 19th century, whereas it is still rising in the other direction. There is no clear difference in invasion success between the two directions, so neither the imperialism dogma (that Eurasian species are exceptionally successful invaders) is supported, nor is the contradictory hypothesis that North America offers more biotic resistance to invaders than Europe because of its less disturbed and richer biota. Our results do not support the tens rule either: that ≈10% of all introduced species establish themselves and that ≈10% of established species spread. We find a success of ≈50% at each step. In comparison, only ≈5% of native vertebrates were introduced in either direction. These figures show that, once a vertebrate is introduced, it has a high potential to become invasive. Thus, it is crucial to minimize the number of species introductions to effectively control invasive vertebrates.

Thema: biotic resistance, ecological imperialism, invasive species, tens rule, time lags

Consumer-food systems: why type I functional responses are exclusive to filter feeders

Biological Reviews 29(2)

Jeschke, J.M.; Kopp, M.; Tollrian, R.

Cambridge Journals | 2004-05-04

Erschienen in: Biological Reviews, Volume 79, Issue 02, pp 337-349 (May 2004) ...

The functional response of a consumer is the relationship between its consumption rate and the abundance of its food. A functional response is said to be of type I if consumption rate increases linearly with food abundance up to a threshold level at which it remains constant. According to conventional wisdom, such type I responses are more frequent among filter feeders than among other consumers. However, the validity of this claim has never been tested. We review 814 functional responses from 235 studies, thereby showing that type I responses are not only exceptionally frequent among filter feeders but that they have only been reported from these consumers. These findings can be understood by considering the conditions that a consumer must fulfil in order to show a type I response. First, the handling condition: the consumer must have a negligibly small handling time (i.e. the time needed for capturing and eating a food item), or it must be able to search for and to capture food while handling other food. Second, the satiation condition: unless its gut is completely filled and gut passage time is minimal, the consumer must search for food at a maximal rate with maximal effort. It thus has to spend much time on foraging (i.e. searching for food and handling it). Our functional response review suggests that only filter feeders sometimes meet both of these conditions. This suggestion is reasonable because filter feeders typically fulfil the handling condition and can meet the satiation condition without losing time, for they are, by contrast to non-filter feeders, able simultaneously to perform foraging and non-foraging activities, such as migration or reproduction.

Thema: filter feeders; foraging time; predators; searching effort; suspension feeders; time budgets; type I functional responses; type II functional responses; type III functional responses; dome-shaped functional responses

Predator functional responses: discriminating between handling and digesting prey

Ecological Monographs 72(1)

Jeschke, J.M.; Kopp, M.; Tollrian, R.

Erschienen in: Ecological Monographs, 72(1), 2002, pp. 95–112 ...

We present a handy mechanistic functional response model that realistically incorporates handling (i.e., attacking and eating) and digesting prey. We briefly review current functional response theory and thereby demonstrate that such a model has been lacking so far. In our model, we treat digestion as a background process that does not prevent further foraging activities (i.e., searching and handling). Instead, we let the hunger level determine the probability that the predator searches for new prey. Additionally, our model takes into account time wasted through unsuccessful attacks. Since a main assumption of our model is that the predator’s hunger is in a steady state, we term it the steady-state satiation (SSS) equation. The SSS equation yields a new formula for the asymptotic maximum predation rate (i.e., asymptotic maximum number of prey eaten per unit time, for prey density approaching infinity). According to this formula, maximum predation rate is determined not by the sum of the time spent for handling and digesting prey, but solely by the larger of these two terms. As a consequence, predators can be categorized into two types: handling-limited predators (where maximum predation rate is limited by handling time) and digestion-limited predators (where maximum predation rate is limited by digestion time). We give examples of both predator types. Based on available data, we suggest that most predators are digestion limited. The SSS equation is a conceptual mechanistic model. Two possible applications of this model are that (1) it can be used to calculate the effects of changing predator or prey characteristics (e.g., defenses) on predation rate and (2) optimal foraging models based on the SSS equation are testable alternatives to other approaches. This may improve optimal foraging theory, since one of its major problems has been the lack of alternative models.

Thema: consumer-resource systems; consumption rate; digestion-limited predators; digestion time; functional response models; handling-limited predators; handling time; hunger level; predation rate; predator–prey systems; steady-state satiation (SSS) equation

Density-dependent effects of prey defences

Jeschke, J.M.; Tollrian, R.

Springer (Germany) | 2000

Erschienen in: Oecologia 123, pp 391-396 (2000)

In this study, we show that the protective advantage of a defence depends on prey density. For our investigations, we used the predator-prey model system Chaoborus-Daphnia pulex. The prey, D. pulex, forms neckteeth as an inducible defence against chaoborid predators. This morphological response effectively reduces predator attack efficiency, i.e. number of successful attacks divided by total number of attacks. We found that neckteeth-defended prey suffered a distinctly lower predation rate (prey uptake per unit time) at low prey densities. The advantage of this defence decreased with increasing prey density. We expect this pattern to be general when a defence reduces predator success rate, i.e. when a defence reduces encounter rate, probability of detection, probability of attack, or efficiency of attack. In addition, we experimentally simulated the effects of defences which increase predator digestion time by using different sizes of Daphnia with equal vulnerabilities. This type of defence had opposite density-dependent effects: here, the relative advantage of defended prey increased with prey density. We expect this pattern to be general for defences which increase predator handling time, i.e. defences which increase attacking time, eating time, or digestion time. Many defences will have effects on both predator success rate and handling time. For these defences, the predator’s functional response should be decreased over the whole range of prey densities.

Thema: Chaoborus obscuripes, Daphnia pulex, Density dependence, Functional response, Inducible defences