Author: Cleo Bertelsmeier

Olivia has just published another chapter of her PhD thesis. Congratulations! It is about the extent of niche shifts using micro- vs macroclimatic data. Link.

Introduced species can establish in climates outside of their native niche and undergo ‘niche shifts’. However, studies of niche shifts generally rely on above-ground climate data, neglecting the potential buffering effect of ground-level or soil climates. 

Here, we investigated the impact of soil temperatures on niche shifts in 95 introduced ant species using both ordination and hypervolume-based approaches. We compared niche shifts using air temperature and soil temperature. 

Overall, between 65.2% and 82% of species (depending on the metric) exhibited smaller niche shifts when considering soil temperature, with varying levels of correlation between air- and soil-temperature niche shifts across species (Correlation coefficient range: 0.56-0.73). Furthermore, air and soil climate conditions were generally more uncoupled than expected at random. This suggests that species use microrefugia and that this may explain the lower levels of niche shifts observed when using microclimatic conditions. Ecological traits, nesting type, forest cover and spatial spread did not consistently impact the differences across metrics in soil temperature buffering of niche shifts among species. This highlights the need for experimental microclimatic research to explore species differences in air- vs. ground-climatic niche shifts.

 We overall highlight the importance of incorporating ecologically relevant microclimatic data, particularly for small, ground-dwelling organisms like ants. This study emphasises the ongoing need for a nuanced understanding of the intricate interplay between air and soil temperatures in the context of niche dynamics. Ultimately, soil-level datasets may improve habitat suitability models, leading to more accurate predictions of establishment success for introduced species. 

We have published a review paper on ‘Temporal dynamics and global flows of insect invasions in an era of globalization’. This was a nice collaborative team effort with the participation of Aymeric, Tongyi, Rosaëlle and Sébastien in addition to Jeff (who is a professor from the University of of New Hampshire and did a sabbatical last year in our team) and Cleo (who lead the paper). Link to the paper.

Summary: Human-mediated transport has led to the establishment of more than 6,700 non-native insect species with wide-ranging effects on ecosystems, economies and human health. Understanding how different aspects of globalization affect the spread of non-native insects is crucial to reducing their effects. In this Review, we explore current and historical patterns, drivers and dynamics of global insect invasions facilitated by humans since prehistory. Multiple aspects of the history of globalization have influenced invasion dynamics, including the spread of agricultural practices in the Neolithic period, the advent of early empires and their trade routes, colonization, geopolitical events, wars and economic crises. Technological innovations such as steam ships, containerization and the internet have further accelerated global insect invasions. Spatial invasion patterns are characterized by frequent secondary spread via bridgehead populations, asymmetric intercontinental species flows originating disproportionally from Europe, and biotic homogenization of communities. Insect invasions are predicted to increase dramatically and their dynamics will shift, especially with the opening of trade routes and introduction pathways. Inspection at ports of entry and early detection systems are crucial to inform mitigation efforts. Future interdisciplinary collaborations will integrate knowledge from diverse and emerging data sources and technologies, advancing our understanding of insect invasion biology.

Globalisation has spread thousands of invasive insect species into new world regions, causing severe losses in ecosystem services. Previous work proposed that plant invasions facilitate insect invasions through the creation of niches for non-native herbivores. Despite the impact of insect invasions, a comprehensive understanding is lacking on how invasion success varies among insect feeding groups. We therefore compiled the predominant larval trophic groups (herbivores, predators, parasites, detritivores, brood-carers) for 5,839 non-native insect species in nine world regions to compare (1) proportions of species in each group between non-native species and the world’s fauna, (2) how invasion success for each trophic group has changed over the last three centuries, and (3) how historical herbivore invasions are related to plant invasions over time, and parasite invasions are related to herbivores. We find that herbivores represent a significantly larger proportion (52.4%) among non-native insects compared to the world fauna (38.4%), whereas proportions of non-native detritivores (including fungivores), predators and brood-carers are significantly lower; parasite proportions do not significantly differ. Predators and detritivores dominated among invasions in the 18th century but subsequently diminished, likely due to changing invasion pathways, while proportions of herbivores, parasites and brood-carers increased over time. We found herbivore invasions to lag 80 years behind plant invasions, whereas parasitoids appear to co-invade with their herbivore hosts. The dominance of herbivores among non-native insects and their strong cross-correlation with plant invasions further strengthens the hypothesis that plant invasions drive the global rise in numbers of non-native insects. 

Link to the paper.

Invasions by non-native insect species can cause massive disruptions to biodiversity and ecological processes which often result in serious economic impacts. 

The trend of increasing numbers of insect invasions worldwide can be traced to a large extent to the the increasing volume  global trade and travel which results in the accidental transport of insects to new regions. Climate change can also create conditions that facilitate the establishment of non-native insects. 

However, there is another reason for the growing number of insect invasions that has garnered less attention. This reason is that the proliferation of non-native plants worldwide is creating many new ecological “niches” for plant-feeding insects thereby facilitating the establishment of a growing number of  these insect species outside their native ranges where their hosts are planted or are invasive. Aroound the world, non-native plants are increasingly common, either as a result of them being planted for purposes of ornamental landscaping, agriculture and forestry. Furthermore, many species of invasive plants are spreading and displacing native species, in forests and other natural areas.

We have just published a paper in collaboration with several international colleagues in the journal BioScience that synthesized (1) mechanisms by which plant invasions facilitate insect invasions; (2) the broad-scale patterns that shed light on the link between plant and insect invasions and; (3) case studies of plant invasions that have facilitated subsequent insect establishment. The body of evidence summarized in the BioScience paper shows that plant invasions are a major driver of insect invasions. This provides additional justification for ramping up efforts aimed at limiting the global spread of non-native plants – to avert the proliferation of non-native insects and their spillover onto native plant species. Worryingly, the evidence also suggests a massive “invasion debt” – many thousands of planted and naturalized non-native plants are waiting to welcome insects from their native ranges thereby launching many more potentially damaging invasions. The stage has unfortunately been set for furhter and growing problems with insect invasions in the future, and this hightens the value of national and international biosecurity programs targeting the exclusion of potentially damaging species.

Gyda has published a new study on accidentally dispersed insect predators and parasitoids. Introductions of insect predators and parasitoids for biological control are a key method for pest management. Yet in recent decades, biological control has become more strictly regulated and less frequent. Conversely, the rate of unintentional insect introductions through human activities is rising. While accidental introductions of insect natural enemies can potentially have serious ecological consequences, they are challenging to quantify as their movements go largely unobserved. We used historical border interception records collected by the US Department of Agriculture from 1913 to 2018 to describe the diversity of entomophagous insects transported unintentionally, their main introduction pathways, and trends in host specificity. There were 35,312 interceptions of insect predators and parasitoids during this period, representing 93 families from 11 orders, and 196 species from these families. Commodity associations varied, but imported plants and plant products were the main introduction pathway. 

Read the full paper here: Link