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The success of invasive species has been explained by two contrasting but non-exclusive views: (i) intrinsic factors make some species inherently good invaders; (ii) species become invasive as a result of extrinsic ecological and genetic influences such as release from natural enemies, hybridization or other novel ecological and evolutionary interactions. These viewpoints are rarely distinguished but hinge on distinct mechanisms leading to different management scenarios. To improve tests of these hypotheses of invasion success we introduce a simple mathematical framework to quantify the invasiveness of species along two axes: (i) interspecific differences in performance among native and introduced species within a region, and (ii) intraspecific differences between populations of a species in its native and introduced ranges. Applying these equations to a sample dataset of occurrences of 1,416 plant species across Europe, Argentina, and South Africa, we found that many species are common in their native range but become rare following introduction; only a few introduced species become more common. Biogeographical factors limiting spread (e.g. biotic resistance, time of invasion) therefore appear more common than those promoting invasion (e.g. enemy release). Invasiveness, as measured by occurrence data, is better explained by inter-specific variation in invasion potential than biogeographical changes in performance. We discuss how applying these comparisons to more detailed performance data would improve hypothesis testing in invasion biology and potentially lead to more efficient management strategies.
Functional traits are useful for comparing the resource use of invasive and native species, with goals of identifying resource overlap to predict competitive interactions. The invasion of northeastern North America by the woodwasp Sirex noctilio has resulted in competition with the native congeneric Sirex nigricornis for suppressed and weakened pines. We compared sizes of adults, venom glands, fecundity, tree species use, voltinism and abundance of the invasive woodwasp S. noctilio with the native S. nigricornis in northeastern North American pines. Rearing adults from attacked pines showed that these species used the same tree species but S. noctilio were far more abundant, especially with increasing time since establishment. Adults of the invasive S. noctilio were larger than S. nigricornis, female S. noctilio had larger glands carrying phytotoxic venom in relation to body size, average-sized S. noctilio females carried more eggs, and S. noctilio developed faster than S. nigricornis. Sirex noctilio was the dominant woodwasp infesting suppressed pines in our study areas. We hypothesize that the future abundance of S. nigricornis could depend in part on the availability of wood for oviposition by this native that is not available or acceptable to the earlier-emerging S. noctilio.
Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands
(2022)
Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.
Location: Canary Islands, Spain.
Major taxa studied: Spermatophytes.
Time period: Present day.
Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non-endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non-endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.
Results: Trait space of endemic and non-endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non-endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.
Main conclusions: We found that endemic and non-endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.
Analyses of species functional traits are suitable to better understand the coexistence of species in a given environment. Trait information can be applied to investigate diversity patterns along environmental gradients and subsequently to predict and mitigate threats associated with climate change and land use. Species traits are used to calculate community trait means, which can be related to environmental gradients. However, while species traits can provide insights into the mechanisms underlying community assembly, they can lead to erroneous inferences if mean trait values are used. An alternative is to incorporate intraspecific trait variability (ITV) into calculating the community trait means. This approach gains increasing acceptance in plant studies. For macrofungi, functional traits have recently been applied to examine their community ecology but, to our knowledge, ITV has yet to be incorporated within the framework of community trait means. Here, we present a conceptual summary of the use of ITV to investigate the community ecology of macrofungi, including the underlying ecological theory. Inferences regarding community trait means with or without the inclusion of ITV along environmental gradients are compared. Finally, an existing study is reconsidered to highlight the variety of possible outcomes when ITV is considered. We hope this Opinion will increase awareness of the potential for within-species trait variability and its importance for statistical inferences, interpretations, and predictions of the mechanisms structuring communities of macro- and other fungi.
Aim: The identification of the mechanisms determining spatial variation in biological diversity along elevational gradients is a central objective in ecology and biogeography. Here, we disentangle the direct and indirect effects of abiotic drivers (climatic conditions, and land use) and biotic drivers (vegetation structure and food resources) on functional diversity and composition of bird and bat assemblages along a tropical elevational gradient. Location: Southern slopes of Mt. Kilimanjaro, Tanzania, East Africa. Methods: We counted birds and recorded bat sonotypes on 58 plots distributed in near-natural and anthropogenically modified habitats from 700 to 4,600 m above sea level. For the recorded taxa, we compiled functional traits related to movement, foraging and body size from museum specimens and databases. Further, we recorded mean annual temperature, precipitation, vegetation complexity as well as the number of fruits, flowers, and insect biomass as measures of resource availability on each study site. Results: Using path analyses, we found similar responses of bird and bat functional diversity to the variation in abiotic and biotic drivers along the elevational gradient. In contrast, the functional composition of both taxa showed distinct responses to abiotic and biotic drivers. For both groups, direct temperature effects were most important, followed by resource availability, precipitation and vegetation complexity. Main Conclusions: Our findings indicate that physiological and metabolic constraints imposed by temperature and resource availability determine the functional diversity of bird and bat assemblages, whereas the composition of individual functional traits is driven by taxon-specific processes. Our study illustrates that distinct filtering mechanisms can result in similar patterns of functional diversity along broad environmental gradients. Such differences need to be taken into account when it comes to conserving the functional diversity of flying vertebrates on tropical mountains.
Mutualistic interactions between plants and animals can affect both plant and animal communities, and potentially leave imprints on plant demography. Yet, no study has simultaneously tested how trait variation in plant resources shapes the diversity of animal consumers, and how these interactions influence seedling recruitment. Here, we analyzed whether (i) phylogenetic diversity and functional diversity of fruiting plants were correlated with the corresponding diversity of frugivorous birds, and (ii) whether phylogenetic diversity and functional identity of plant and bird communities influenced the corresponding diversity and identity of seedling communities. We recorded mutualistic interactions between fleshy-fruited plants and frugivorous birds and seedling communities in 10 plots along an elevational gradient in the Colombian Andes. We built a phylogeny for plants/seedlings and birds and measured relevant morphological plant and bird traits that influence plant-bird interactions and seedling recruitment. We found that phylogenetic diversity and functional diversity of frugivorous birds were positively associated with the corresponding diversities of fruiting plants, consistent with a bottom-up effect of plants on birds. Moreover, the phylogenetic diversity of seedlings was related to the phylogenetic diversity of plants, but was unrelated to the phylogenetic diversity of frugivorous birds, suggesting that top-down effects of animals on seedlings were weak. Mean seed mass of seedling communities was positively associated with the mean fruit mass of plants, but was not associated with the mean avian body mass in the frugivore communities. Our study shows that variation in the traits of fleshy-fruited plants was associated with the diversity of frugivorous birds and affected the future trajectory of seedling recruitment, whereas the morphological traits of animal seed dispersers were unrelated to the phylogenetic and functional structure of seedling communities. These findings suggest that bottom-up effects are more important than top-down effects for seed-dispersal interactions and seedling recruitment in diverse tropical communities.
Aim
How species respond to climate change is influenced by their sensitivity to climatic conditions (i.e. their climatic niche) and aspects of their adaptive capacity (e.g. their dispersal ability and ecological niche). To date, it is largely unknown whether and how species’ sensitivity to climate change and their adaptive capacity covary. However, understanding this relationship is important to predict the potential consequences of a changing climate for species assemblages. Here, we test how species’ sensitivity to climate change and trait-based measures of their ecological adaptive capacity (i) vary along a broad elevational gradient and (ii) covary across a large number of bird species.
Location
A Neotropical elevational gradient (300–3600 m.a.s.l.) in the Manú Biosphere Reserve, south-east Peru.
Methods
We focus on 215 frugivorous bird species along a Neotropical elevational gradient. We approximate species’ sensitivity to climate change by their climatic niche breadth, based on species occurrences across South America and bioclimatic variables. In addition, we use a trait-based approach to estimate the dispersal ability of species (approximated by their wing pointedness), their dietary niche breadth (approximated by bill width) and their habitat niche breadth (the number of used habitat classes).
Results
We found that (i) species’ climatic niche breadth increased with elevation, while their trait-based dispersal ability and dietary niche breadth decreased with elevation, and (ii) sensitivity to climate change and trait-based adaptive capacity were not related across species.
Main conclusions
These results suggest different mechanisms of how species in lowland and highland assemblages might respond to climate change. The independent variation of species’ sensitivity to climate change and their trait-based adaptive capacity suggests that accounting for both dimensions will improve assessments of species’ susceptibility to climate change and potential impacts of climate change on diverse species assemblages.
Um Ursachen und Ausmaß der zukünftigen Veränderungen von Flora und Pflanzengesellschaften des Grünlandes analysieren und abschätzen zu können, wurde der aktuelle Zustand dieser Vegetation in einem 50 km2 großen Landschaftsausschnitt im westlichen Hunsrück beschrieben, typisiert und flächendeckend kartiert. Hauptursache für Veränderungen ist die Intensivierung der Bewirtschaftung, wobei die Steigerung der Düngung, die wachsende Zahl der Nutzungseingriffe, die Vereinheitlichung der Bewirtschaftung auf großen Schlägen durch wenige Betriebe die für das Grünland wichtigsten Faktoren sind. Deshalb wurde die Vegetation der Wiesen und Weiden anhand einer Trophieskala typisiert, die die Nährstoffversorgung und damit die Bewirtschaftungsintensität widerspiegelt. Die Basis dafür bilden Vegetationsaufnahmen und nach Abundanz gewichtete Gesamtartenlisten von Grünlandschlägen.
Schon heute sind magere Grünlandflächen auch in diesem Mittelgebirge selten geworden. Pflanzenarten mit auffälliger Rückgangstendenz wurden im Gesamtgebiet kartiert und auf ihre Eigenschaften hin bewertet, die wesentlich zu ihrer Konkurrenzschwäche im intensiv genutzten Grünland beitragen. Alle diese rückläufigen Arten waren im Untersuchungsgebiet wahrscheinlich noch bis 1950/1960 weit verbreitet. Ihre Populationen sind heute in kleine, weitgehend isolierte Teilpopulationen aufgespalten, deren Überlebenschancen sich dadurch zusammen mit an sie gebundenen Tierarten rasch weiter verringern dürften.