Fragmentation—the process by which habitats are transformed into smaller patches isolated from each other—has been identified as a major threat for biodiversity. Fragmentation has well-established ...demographic and population genetic consequences, eroding genetic diversity and hindering gene flow among patches. However, fragmentation should also select on life history, both predictably through increased isolation, demographic stochasticity and edge effects, and more idiosyncratically via altered biotic interactions. While species have adapted to natural fragmentation, adaptation to anthropogenic fragmentation has received little attention. In this review, we address how and whether organisms might adapt to anthropogenic fragmentation. Drawing on selected case studies and evolutionary ecology models, we show that anthropogenic fragmentation can generate selection on traits at both the patch and landscape scale, and affect the adaptive potential of populations. We suggest that dispersal traits are likely to experience especially strong selection, as dispersal both enables migration among patches and increases the risk of landing in the inhospitable matrix surrounding them. We highlight that suites of associated traits are likely to evolve together. Importantly, we show that adaptation will not necessarily rescue populations from the negative effects of fragmentation, and may even exacerbate them, endangering the entire metapopulation.
This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.
Insect invasions, the establishment and spread of nonnative insects in new regions, can have extensive economic and environmental consequences. Increased global connectivity accelerates rates of ...introductions, while climate change may decrease the barriers to invader species' spread. We follow an individual-level insect- and arachnid-centered perspective to assess how the process of invasion is influenced by phenotypic heterogeneity associated with dispersal and stress resistance, and their coupling, across the multiple steps of the invasion process. We also provide an overview and synthesis on the importance of environmental filters during the entire invasion process for the facilitation or inhibition of invasive insect population spread. Finally, we highlight important research gaps and the relevance and applicability of ongoing natural range expansions in the context of climate change to gain essential mechanistic insights into insect invasions.
Climate warming affects the rate and timing of the development in ectothermic organisms. Short-living, ectothermic organisms (including many insects) showing thermal plasticity in life-cycle ...regulation could, for example, increase the number of generations per year under warmer conditions. However, changed phenology may challenge the way organisms in temperate climates deal with the available thermal time window at the end of summer. Although adaptive plasticity is widely assumed in multivoltine organisms, rapid environmental change could distort the quality of information given by environmental cues that organisms use to make developmental decisions. Developmental traps are scenarios in which rapid environmental change triggers organisms to pursue maladaptive developmental pathways. This occurs because organisms must rely upon current environmental cues to predict future environmental conditions and corresponds to a novel case of ecological or evolutionary traps. Examples of introduced, invasive species are congruent with this hypothesis. Based on preliminary experiments, we argue that the dramatic declines of the wall brown Lasiommata megera in northwestern Europe may be an example of a developmental trap. This formerly widespread, bivoltine (or even multivoltine) butterfly has become a conundrum to conservationist biologists. A split-brood field experiment with L. megera indeed suggests issues with life-cycle regulation decisions at the end of summer. In areas where the species went extinct recently, 100% of the individuals developed directly into a third generation without larval diapause, whereas only 42.5% did so in the areas where the species still occurs. Under unfavourable autumn conditions, the attempted third generation will result in high mortality and eventually a lost or ‘suicidal’ third generation in this insect with non-overlapping, discrete generations. We discuss the idea of a developmental trap within an integrated framework for assessing the vulnerability of species to climate change.
ABSTRACT
Intimate associations between different species drive community composition across ecosystems. Understanding the ecological and evolutionary drivers of these symbiotic associations is ...challenging because their structure eventually determines stability and resilience of the entire species network. Here, we compiled a detailed database on naturally occurring ant–symbiont networks in Europe to identify factors that affect symbiont network topology. These networks host an unrivalled diversity of macrosymbiotic associations, spanning the entire mutualism–antagonism continuum, including: (i) myrmecophiles – commensalistic and parasitic arthropods; (ii) trophobionts – mutualistic aphids, scale insects, planthoppers and caterpillars; (iii) social parasites – parasitic ant species; (iv) parasitic helminths; and (v) parasitic fungi. We dissected network topology to investigate what determines host specificity, symbiont species richness, and the capacity of different symbiont types to switch hosts. We found 722 macrosymbionts (multicellular symbionts) associated with European ants. Symbiont type explained host specificity and the average relatedness of the host species. Social parasites were associated with few hosts that were phylogenetically highly related, whereas the other symbiont types interacted with a larger number of hosts across a wider taxonomic distribution. The hosts of trophobionts were the least phylogenetically related across all symbiont types. Colony size, host range and habitat type predicted total symbiont richness: ant hosts with larger colony size, a larger distribution range or with a wider habitat range contained more symbiont species. However, we found that different sets of host factors affected diversity in the different types of symbionts. Ecological factors, such as colony size, host range and niche width predominantly determined myrmecophile species richness, whereas host phylogeny was the most important predictor of mutualistic trophobiont, social parasite and parasitic helminth species richness. Lastly, we found that hosts with a common biogeographic history support a more similar community of symbionts. Phylogenetically related hosts also shared more trophobionts, social parasites and helminths, but not myrmecophiles. Taken together, these results suggest that ecological and evolutionary processes structure host specificity and symbiont richness in large‐scale ant–symbiont networks, but these drivers may shift in importance depending on the type of symbiosis. Our findings highlight the potential of well‐characterized bipartite networks composed of different types of symbioses to identify candidate processes driving community composition.
Humans fundamentally affect dispersal, directly by transporting individuals and indirectly by altering landscapes and natural vectors. This human-mediated dispersal (HMD) modifies long-distance ...dispersal, changes dispersal paths, and overall benefits certain species or genotypes while disadvantaging others. HMD is leading to radical changes in the structure and functioning of spatial networks, which are likely to intensify as human activities increase in scope and extent. Here, we provide an overview to guide research into HMD and the resulting rewiring of spatial networks, making predictions about the ecological and evolutionary consequences and how these vary according to spatial scale and the traits of species. Future research should consider HMD holistically, assessing the range of direct and indirect processes to understand the complex impacts on eco-evolutionary dynamics.
Research into human impacts on biodiversity would benefit from considering HMD as a central process, in particular the wide variety of anthropogenic influences on the dispersal of organisms.
Particular species or genotypes benefit from increased dispersal ability under HMD, including new linkages among areas of suitable habitat; conversely, others suffer from loss of dispersal opportunities and linkages, as well as increased costs.
In total, HMD is expected to rewire spatial networks through the reconfiguration of links among nodes, particularly by changing the distances over which individuals disperse and the creation of highly connected nodes (hubs).
As human impacts on the environment increase, ecology and conservation will benefit from considering rewiring holistically, assessing both the positive and negative impacts of HMD on eco-evolutionary dynamics.
To successfully colonize new habitats, organisms not only need to gain access to it, they also need to cope with the selective pressures imposed by the local biotic and abiotic conditions. The number ...of immigrants, the preadaptation to the local habitat and the presence of competitors are important factors determining the success of colonization. Here, using two experimental set‐ups, we studied the effect of interspecific competition in combination with propagule pressure and preadaptation on the colonization success of new habitats. Our model system consisted of tomato plants (the novel habitat), the two‐spotted spider mite Tetranychus urticae as our focal species and the red spider mite Tetranychus evansi as a competitor. Our results show that propagule pressure and preadaptation positively affect colonization success. More successful populations reach larger final population sizes either by having higher per capita growth rates (due to preadaptation effects) or by starting a population with a larger number of individuals. Although populations are more successful colonizing non‐competitive environments than competitive ones, propagule pressure and preadaptation counteract the negative effects of competition, promoting colonization success. Our study shows the importance of propagule pressure and preadaptation for successful colonization of new habitats by providing the ability to cope with both the exigencies of new environments and the community context.
The increasing urbanization process is hypothesized to drastically alter (semi‐)natural environments with a concomitant major decline in species abundance and diversity. Yet, studies on this effect ...of urbanization, and the spatial scale at which it acts, are at present inconclusive due to the large heterogeneity in taxonomic groups and spatial scales at which this relationship has been investigated among studies. Comprehensive studies analysing this relationship across multiple animal groups and at multiple spatial scales are rare, hampering the assessment of how biodiversity generally responds to urbanization. We studied aquatic (cladocerans), limno‐terrestrial (bdelloid rotifers) and terrestrial (butterflies, ground beetles, ground‐ and web spiders, macro‐moths, orthopterans and snails) invertebrate groups using a hierarchical spatial design, wherein three local‐scale (200 m × 200 m) urbanization levels were repeatedly sampled across three landscape‐scale (3 km × 3 km) urbanization levels. We tested for local and landscape urbanization effects on abundance and species richness of each group, whereby total richness was partitioned into the average richness of local communities and the richness due to variation among local communities. Abundances of the terrestrial active dispersers declined in response to local urbanization, with reductions up to 85% for butterflies, while passive dispersers did not show any clear trend. Species richness also declined with increasing levels of urbanization, but responses were highly heterogeneous among the different groups with respect to the richness component and the spatial scale at which urbanization impacts richness. Depending on the group, species richness declined due to biotic homogenization and/or local species loss. This resulted in an overall decrease in total richness across groups in urban areas. These results provide strong support to the general negative impact of urbanization on abundance and species richness within habitat patches and highlight the importance of considering multiple spatial scales and taxa to assess the impacts of urbanization on biodiversity.
We studied the effect of local‐ and landscape‐scale urbanization on the abundance and species richness of aquatic (cladocerans), limno‐terrestrial (rotifers) and terrestrial (butterflies, ground beetles, ground‐ and web spiders, macro‐moths, orthopterans and snails) invertebrate groups. Abundances of the terrestrial active dispersers declined, often dramatically, in response to local urbanization, while passive dispersers did not show any clear trend. Species richness also declined with increasing urbanization due to biotic homogenization and/or local species loss, but responses were highly heterogeneous in magnitude and spatial scale. Overall, these results strongly support the general negative impact of urbanization on species communities.
Diverse communities of symbiotic microbes inhabit the digestive systems of vertebrates and play a crucial role in animal health, and host diet plays a major role in shaping the composition and ...diversity of these communities. Here, we characterized diet and gut microbiome of fire salamander populations from three Belgian forests. We carried out DNA metabarcoding on fecal samples, targeting eukaryotic 18S rRNA of potential dietary prey items, and bacterial 16S rRNA of the concomitant gut microbiome. Our results demonstrated an abundance of soft-bodied prey in the diet of fire salamanders, and a significant difference in the diet composition between males and females. This sex-dependent effect on diet was also reflected in the gut microbiome diversity, which is higher in males than female animals. Proximity to human activities was associated with increased intestinal pathogen loads. Collectively, the data supports a relationship between diet, environment and intestinal microbiome in fire salamanders, with potential health implications.
Individuals moving in heterogeneous environments can improve their fitness considerably by habitat choice. Induction by past exposure, genetic preference alleles and comparison of local performances ...can all drive this decision‐making process. Despite the importance of habitat choice mechanisms for eco‐evolutionary dynamics in metapopulations, we lack insights on the connection of their cue with its effect on fitness optimization. We selected a laboratory population of Tetranychus urticae Koch (two‐spotted spider mite) according to three distinct host‐choice selection treatments for ten generations. Additionally, we tested the presence of induced habitat choice mechanisms and quantified the adaptive value of a choice before and after ten generations of artificial selection in order to gather insight on the habitat choice mechanisms at play. Unexpectedly, we observed no evolution of habitat choice in our experimental system: the initial choice of cucumber over tomato remained. However, this choice became maladaptive as tomato ensured a higher fitness at the end of the experiment. Furthermore, a noteworthy proportion of induced habitat choice can modify this ecological trap depending on past environments. Despite abundant theory and applied relevance, we provide the first experimental evidence of an emerging trap. The maladaptive choice also illustrates the constraints habitat choice has in rescuing populations endangered by environmental challenges or in pest control.
PDF
