Agriculture in the XXI century faces the huge challenge of having to provide food to a rapidly growing human population, which is expected to reach 10.9 billion in 2100 (UUNN 2019), by means of practices and methods that guarantee crop sustainability, human health safety, and respect to the environment (UUNN 2015). Such regulation by the United Nations ultimately entails that agricultural scientists are urged to design strategies and methods that effectively minimize the use of harmful chemical products to control pest populations and to improve soil quality.
One of the most, if not the most, sustainable, safe, and environmentally friendly approach to apply against pests is Biological Pest Control (BPC, hereafter), that is, the use of natural enemies to control the populations of pest organisms. The concept of BPC is by no means new: long back to the 300 AC, Chinese farmers built bamboo bridges between citrus trees to facilitate the foraging of the ant species Oecophylla smaragdina to control lepidopteran citrus pests (Konishi and Ito, 1973); It is also nice to use this recommendation letter to recall and quote the words written in 1752 by the famous Swedish taxonomist, botanist and zoologist, Carl Linnaeus: "Every insect has its predator which follows and destroys it. Such predatory insects should be caught and used for disinfecting crop-plants" (Hörstadius (1974) apud Linnaeus 1752).
Acknowledging the many cases of successes from BPC along our recent history, it is also true that application of BPC strategies during the XX century suffered from wrong-doings, mainly when the introduced biological control agent (BCA, hereafter) was of exotic origin and with a generalist diet-breath; in some cases the release of exotic species resulted on global extinction, reduction in the range of distribution, reduction in the population abundance, and partial displacement, of native and functionally similar species, and interbreeding with them (reviewed in van Lenteren et al. 2006). One of the most famous cases is that of Harmonia axyridis, a coccinellid predator of Asian origin that caused important environmental damage in North America (reviewed in Koch & Galvan, 2008).
Fortunately, after the implementation of the Nagoya protocol (CBD, 2011) importation of exotic species for BPC use was severely restricted and controlled, worldwide. Consequently, companies and agricultural scientist were driven to reinforce their focus and interest on the exploitation of native natural enemies, via the mass-rearing and release of native candidates (augmentative BPC), the conservation of landscapes near the crops to provide resources for natural enemies (i.e. conservation biological pest control), or via the exploitation of the genetic variability of BCAs, to create strains performing better at regulating pest populations under specific biotic or abiotic negative circumstances. Some of these cases are cited in Lartigue et al. (2020). The genetic improvement of BCAs is a strategy still in its infancy, but there is no doubt that the interest for it has significantly increased over the last 5 years (Lommen et al 2017, Bielza 2020, Leung et al 2020).
In my humble opinion, what makes the paper of Lartigue et al. (2020) a remarkable contribution to the field of genetic breeding of BCAs is that it opens a new window of opportunities to the field, by exploring the possibilities for artificial selection of behavioral traits (Réale et al. 2007) to "create" strains of natural enemies displaying behavioral syndromes (Sih et al. 2004) that makes them better at regulating pest populations. The behavioral approach for breeding BCAs can then be extended by crossing it with known abiotic and/or biotic hostile environments (e.g. warm and drought environments, presence of predators/competitors to the BCA, respectively) and engineer strains more prompt to display particular behavioral syndromes to help them to overcome the overall hostility of specific environments. I strongly believe that the approach proposed in Lartigue et al. (2020) will influence the future management of agricultural systems, where strategies including the genetic breeding of BCAs’ behavior will contribute to create better guards and protectors of our crops.

References

Bielza, P., Balanza, V., Cifuentes, D. and Mendoza, J. E. (2020). Challenges facing arthropod biological control: Identifying traits for genetic improvement of predators in protected crops. Pest Manag Sci. doi: https://doi.org/10.1002/ps.5857
CBD - Convention on Biological Diversity, 2011. The Nagoya Protocol on Access and Benefit-sharing, https://www.cbd.int/abs/doc/protocol/nagoya-protocol-en.pdf
Hörstadius, S. (1974). Linnaeus, animals and man. Biological Journal of the Linnaean Society, 6, 269-275. doi: https://doi.org/10.1111/j.1095-8312.1974.tb00725.x
Koch, R.L. and Galvan, T.L. (2008). Bad side of a good beetle: the North American experience with Harmonia axyridis. BioControl 53, 23–35. doi: https://doi.org/10.1007/978-1-4020-6939-0_3
Konishi, M. and Ito, Y. (1973). Early entomology in East Asia. In: Smith, R.F., Mittler, T.E., Smith, C.N. (Eds.), History of Entomology, Annual Reviews Inc., Palo Alto, California, pp. 1-20.
Lartigue, S., Yalaoui, M., Belliard, J., Caravel, C., Jeandroz, L., Groussier, G., Calcagno, V., Louâpre, P., Dechaume-Moncharmont, F.-X., Malausa, T. and Moreau, J. (2020). Consistent variations in personality traits and their potential for genetic improvement of biocontrol agents: Trichogramma evanescens as a case study. bioRxiv, 2020.08.21.257881, ver. 4 peer-reviewed and recommended by PCI Ecology. doi: https://doi.org/10.1101/2020.08.21.257881
Leung et al. (2020). Next-generation biological control: the need for integrating genetics and genomics. Biological Reviews, 95(6), 1838–1854. doi: https://doi.org/10.1111/brv.12641
Lommen, S. T. E., de Jong, P. W. and Pannebakker, B. A. (2017). It is time to bridge the gap between exploring and exploiting: prospects for utilizing intraspecific genetic variation to optimize arthropods for augmentative pest control – a review. Entomologia Experimentalis et Applicata, 162: 108-123. doi: https://doi.org/10.1111/eea.12510
Réale, D., Reader, S. M., Sol, D., McDougall, P. T. and Dingemanse, N. J. (2007). Integrating animal temperament within ecology and evolution. Biological Reviews, 82: 291-318. doi: https://doi.org/10.1111/j.1469-185X.2007.00010.x
Sih, A., Bell, A. and Johnson, J. C. (2004). Behavioral syndromes: an ecological and evolutionary overview. Trends in Ecology and Evolution, 19(7), 372–378. doi: https://doi.org/10.1016/j.tree.2004.04.009
UUNN. 2015. Transforming our world: the 2030 Agenda for Sustainable Development. report of the Open Working Group of the General Assembly on Sustainable Development Goals (A/68/970 and Corr.1; see also A/68/970/Add.1–3).
UUNN. 2019. World population prospects 2019. United Nations, Department of Economic and Social Affairs, Population Division: Highlights. ST/ESA/SER.A/423.
van Lenteren, J. C., Bale, J., Bigler, F., Hokkanen, H. M. T. and Loomans A. J. M. (2006). Assessing risks of releasing exotic biological control agents of arthropod pests. Annual Review of Entomology, 51: 609-634. doi: https://doi.org/10.1146/annurev.ento.51.110104.151129

Individuals ability to withstand abiotic and biotic stresses is crucial to the maintenance of populations at climate edge of tree species distribution. We start to have a detailed understanding of tree growth response and to a lesser extent mortality response in these populations. In contrast, our understanding of the response of tree fecundity and recruitment remains limited because of the difficulty to monitor it at the individual tree level in the field. Tree recruitment limitation is, however, crucial for tree population dynamics [1-2].
In their study Oddou-Muratorio et al. [3] use a new method that they recently developed that jointly estimate male and female effective fecundity in natural populations using naturally established seedlings [4]. Their method uses a spatially explicit Bayesian analysis based on molecular markers and parentage analyses (MEMM program [4]). They apply this method to an unmanaged Beech forest at the southern edge of Beech distribution, where tree defoliation – taken as an integrative indicator of tree abiotic and biotic stress – and growth have been monitored for all adult trees.
This allows the authors to explore alternative hypothesis about tree fecundity response to stress. In one hand, biotic and abiotic stresses are thought to negatively impact tree fecundity. In the other hand, management and studies of orchard fruit tree support the idea that stress could trigger a compensatory increase of fecundity at the cost of other performances such as growth and survival.
They show that both growth and female fecundity are negatively affected by defoliation. There was no evidence that stresses trigger a compensatory increase of fecundity. Yet, they also found that, for large highly defoliated trees, there was a trade-off between growth and female fecundity. Some individuals are able to mitigate stress impact on fecundity by decreasing their growth. It is difficult to understand with available data what is driving such divergent responses between defoliated individuals. This could be related to differences in micro-environmental conditions or genetic background of individual trees. Such individual-level difference in response to stress could be crucial to understand tree populations response to ongoing climate change. This study clearly opens exciting new perspectives to apply such new methods to understand the role of fecundity on tree population dynamics. For instance, could we apply this method across the species distribution to understand how effective fecundity and its response to abiotic stress change between southern edge populations, core populations, and northern edge populations? Using time-series retrieved from such analysis can we disentangle the effect of different climatic drivers? It would also be interesting to see how such results can contribute to analyses covering the full tree life cycle to understand the contribution of fecundity response to population and evolutionary.

References

[1] Clark, J. S. et al. (1999). Interpreting recruitment limitation in forests. American Journal of Botany, 86(1), 1-16. doi: 10.2307/2656950
[2] Petit, R. J., and Hampe, A. (2006). Some evolutionary consequences of being a tree. Annu. Rev. Ecol. Evol. Syst., 37, 187-214. doi: 10.1146/annurev.ecolsys.37.091305.110215
[3] Oddou-Muratorio, S., Petit, C., Journe, V., Lingrand, M., Magdalou, J. A., Hurson, C., Garrigue, J., Davi, H. and Magnanou, E. (2019). Crown defoliation decreases reproduction and wood growth in a marginal European beech population. bioRxiv, 474874, ver. 4 peer-reviewed and recommended by PCI Ecology. doi: 10.1101/474874
[4] Oddou‐Muratorio, S. and Klein, E. K. (2008). Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species. Molecular Ecology, 17(11), 2743-2754. doi: 10.1111/j.1365-294X.2008.03783.x

Species Distribution Models (SDMs) are one of the most commonly used tools to predict where species are, where they may be in the future, and, at times, what are the variables driving this prediction. As such, applying an SDM to a dataset is akin to making a bet: that the known occurrence data are informative, that the resolution of predictors is adequate vis-à-vis the scale at which their impact is expressed, and that the model will adequately capture the shape of the relationships between predictors and predicted occurrence.

In this contribution, Lambert & Virgili (2023) perform a comprehensive assessment of different sources of complications to this process, using replicated simulations of two synthetic species. Their experimental process is interesting, in that both the data generation and the data analysis stick very close to what would happen in "real life". The use of synthetic species is particularly relevant to the assessment of SDM robustness, as they enable the design of species for which the shape of the relationship is given: in short, we know what the model should capture, and can evaluate the model performance against a ground truth that lacks uncertainty.

Any simulation study is limited by the assumptions established by the investigators; when it comes to spatial data, the "shape" of the landscape, both in terms of auto-correlation and in where the predictors are available. Lambert & Virgili (2023) nicely circumvent these issues by simulating synthetic species against the empirical distribution of predictors; in other words, the species are synthetic, but the environment for which the prediction is made is real. This is an important step forward when compared to the use of e.g. neutral landscapes (With 1997), which can have statistical properties that are not representative of natural landscapes (see e.g. Halley et al., 2004).

A striking point in the study by Lambert & Virgili (2023) is that they reveal a deep, indeed deeper than expected, stochasticity in SDMs; whether this is true in all models remains an open question, but does not invalidate their recommendation to the community: the interpretation of outcomes is a delicate exercise, especially because measures that inform on the goodness of the model fit do not capture the predictive quality of the model outputs. This preprint is both a call to more caution, and a call to more curiosity about the complex behavior of SDMs, while also providing a sensible template to perform future analyses of the potential issues with predictive models.

References

Halley, J. M., et al. (2004) “Uses and Abuses of Fractal Methodology in Ecology: Fractal Methodology in Ecology.” Ecology Letters, vol. 7, no. 3, pp. 254–71. https://doi.org/10.1111/j.1461-0248.2004.00568.x.

Lambert, Charlotte, and Auriane Virgili (2023). Data Stochasticity and Model Parametrisation Impact the Performance of Species Distribution Models: Insights from a Simulation Study. bioRxiv, ver. 2 peer-reviewed and recommended by Peer Community in Ecology. https://doi.org/10.1101/2023.01.17.524386

With, Kimberly A. (1997) “The Application of Neutral Landscape Models in Conservation Biology. Aplicacion de Modelos de Paisaje Neutros En La Biologia de La Conservacion.” Conservation Biology, vol. 11, no. 5, pp. 1069–80. https://doi.org/10.1046/j.1523-1739.1997.96210.x.

​​In this article, the authors discuss the results of their study investigating the effects of heat stress and moisture stress on a terrestrial isopod Armadilldium vulgare, the common woodlouse [1]. Specifically, the authors have assessed how increased temperature or decreased moisture affects life history traits (such as growth, survival, and reproduction) as well as physiological traits (immune cell parameters and \( beta \)-galactosidase activity). This article quantitatively evaluates the effects of the two stressors on woodlouse. Terrestrial isopods like woodlouse are sensitive to thermal and moisture stress [2; 3] and are therefore good models to test hypotheses in global change biology and for monitoring ecosystem health.

​An important feature of this study is the combination of experimental, laboratory, and analytical techniques. Experiments were conducted under controlled conditions in the laboratory by modulating temperature and moisture, life history and physiological traits were measured/analyzed and then tested using models. Both stressors had negative impacts on survival and reproduction of woodlouse, and result in premature ageing. Although thermal stress did not affect survival, it slowed woodlouse growth. Moisture stress did not have a detectable effect on woodlouse growth but decreased survival and reproductive success. An important insight from this study is that effects of heat and moisture stressors on woodlouse are not necessarily linear, and experimental approaches can be used to better elucidate the mechanisms and understand how these organisms respond to environmental stress.

​This article is timely given the increasing attention on biological monitoring and ecosystem health.​

References:

[1] Depeux C, Branger A, Moulignier T, Moreau J, Lemaître J-F, Dechaume-Moncharmont F-X, Laverre T, Pauhlac H, Gaillard J-M, Beltran-Bech S (2022) Deleterious effects of thermal and water stresses on life history and physiology: a case study on woodlouse. bioRxiv, 2022.09.26.509512., ver. 3 peer-reviewd and recommended by PCI Ecology. https://doi.org/10.1101/2022.09.26.509512

[2] ​Warburg MR, Linsenmair KE, Bercovitz K (1984) The effect of climate on the distribution and abundance of isopods. In: Sutton SL, Holdich DM, editors. The Biology of Terrestrial Isopods. Oxford: Clarendon Press. pp. 339–367.​

[3] Hassall M, Helden A, Goldson A, Grant A (2005) Ecotypic differentiation and phenotypic plasticity in reproductive traits of Armadillidium vulgare (Isopoda: Oniscidea). Oecologia 143: 51–60.​ https://doi.org/10.1007/s00442-004-1772-3

Modelling the temporal dynamics of trophic networks has been a key challenge for community ecologists for decades, especially when anthropogenic and natural forces drive changes in species composition, abundance, and interactions over time. So far, most modelling methods fail to incorporate the inherent complexity of such systems, and its variability, to adequately describe and predict temporal changes in the topology of trophic networks. 

Taking benefit from theoretical computer science advances, Gaucherel and colleagues (2024) propose a new methodological framework to tackle this challenge based on discrete-event Petri net methodology. To introduce the concept to naïve readers the authors provide a useful example using a simplistic predator-prey model.

The core biological system of the article is a freshwater trophic network of western France in the Charente-Maritime marshes of the French Atlantic coast. A directed graph describing this system was constructed to incorporate different functional groups (phytoplankton, zooplankton, resources, microbes, and abiotic components of the environment) and their interactions. Rules and constraints were then defined to, respectively, represent physiochemical, biological, or ecological processes linking network components, and prevent the model from simulating unrealistic trajectories. Then the full range of possible trajectories of this mechanistic and qualitative model was computed.

The model performed well enough to successfully predict a theoretical trajectory plus two trajectories of the trophic network observed in the field at two different stations, therefore validating the new methodology introduced here. The authors conclude their paper by presenting the power and drawbacks of such a new approach to qualitatively model trophic networks dynamics.

Reference

Cedric Gaucherel, Stolian Fayolle, Raphael Savelli, Olivier Philippine, Franck Pommereau, Christine Dupuy (2024) Diagnosis of planktonic trophic network dynamics with sharp qualitative changes. bioRxiv 2023.06.29.547055, ver. 2 peer-reviewed and recommended by Peer Community in Ecology. https://doi.org/10.1101/2023.06.29.547055