Biodiversity Data Journal :
Research Article
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Corresponding author: Sophie Wallon (sophie.wallon@gmail.com)
Academic editor: Pedro Cardoso
Received: 01 Jun 2023 | Accepted: 21 Sep 2023 | Published: 05 Oct 2023
© 2023 Sophie Wallon, Noelline Tsafack, Gabor Pozsgai, Catarina Melo, Paulo Borges, Rui Elias
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wallon S, Tsafack N, Pozsgai G, Melo C, Borges PAV, Elias R (2023) Effects of a short-term temperature increase on arthropod communities associated with pastures. Biodiversity Data Journal 11: e107385. https://doi.org/10.3897/BDJ.11.e107385
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The impact of climate change on islands is expected to cause dramatic consequences on native biodiversity. However, limited data are available for arthropod communities in island agroecosystems. In this study, we simulate a small-scale climatic change (average of +1.2°C), using Open Top Chambers (OTCs) in forage crops in the Azores Archipelago (Portugal) and test the responses of arthropod communities associated with intensively-managed pastures. At three sites, twenty 1 x 1 m plots were established: 10 treatment plots with OTCs and 10 control plots. Arthropods were sampled with pitfall traps on two sampling events (winter and summer of 2020). When considering all species collected, arthropods' abundance was lower in OTCs. Specific taxa, namely spiders and beetles, showed a fast response to the OTCs' presence. The assemblage of non-indigenous spiders well adapted to pastures showed a significant difference in diversity with a slightly greater richness, but lower abundance inside the warmer plots. However, the presence of OTCs resulted in a decrease in beetle richness and abundance. This decline may be attributed to the multiple effects of warming. Therefore, it is imperative to conduct further investigations to elucidate the ecological processes that underlie the observed patterns.
invertebrates, Azores, climate change, grasses, islands, species diversity
Climate change is happening at a fast pace and the results are the increase in temperature (
In particular, island environments are especially sensitive to climate change and have been identified amongst the most vulnerable ecosystems to climate shifts and extremes (
In the Azores Archipelago, around 56% of the land is dedicated to agroecosystems, of which 46% are permanent pastures (
In the last years, a plethora of studies have shown the impact of global change on arthropods in grasslands, pinpointing how climate change can affect arthropod communities and alter their diversity and/or composition (
We hypothesise that warming will affect arthropod communities and we aim to identify which groups or species of arthropods are more likely to respond positively or negatively to an increase in temperature. We address the following research questions:
i) Does the increase in temperature within OTCs change the species composition? Due to the small-scale and the short-term of the experiment, we predict little or no changes in the species composition and, consequently, that communities will remain highly similar between the two treatments.
ii) Does the increase in temperature in OTCs change the total abundance of arthropods? Based on previous studies, we expect higher total arthropod abundance in OTCs than in the control plots with ambient temperature.
iii) Does the increase in temperature impact the relative abundances of species? We expect shifts in the ratio of common, rare and dominant species, especially an increasing dominance of a few, thermophilus, species.
The study was conducted in three intensively-managed experimental pasture fields on Terceira Island (area 402 km2 and maximum elevation of 1023 m), located in the Azores Archipelago in Portugal (38°37’ N–38°48’ N, 27°02’ W–27°23’ W). The three fields (marked as A, B and C) were located at three different altitudes: 186 m a.s.l. (latitude: 38.703596°N; longitude: -27.353805°W), 301 m a.s.l. (latitude: 38.701639°N; longitude: - 27.325783°W) and 386 m a.s.l. (latitude: 38.697770°N; longitude: -27.170075°W), respectively (Fig.
An in situ experiment was set up using Open Top Chambers (OTCs). OTCs are widely used on climate change investigation in order to modify abiotic conditions in situ and simulate an increase in temperature (
In each field, twenty (1 x 1 m) plots were set up on a grid pattern with 1.5 m space between each plot (Fig.
The sampling was carried out during two seasons (winter and summer of 2020), before the grass had been mown. No cattle were allowed inside the sampling area. It is important to note that the experimental set-up (control and OTCs) was mounted the whole year round. Thus, the OTCs and control plots were not moved between the two sampling seasons.
For this study, we focused on arthropod communities associated with intensive pasture management. As OTCs represent a physical barrier for flying insects and can induce bias into the results, the present study focuses on crawling arthropods. As pitfall traps target crawling arthropods, they were used for sampling. Four pitfall traps were set on each outside corner of each plot giving a total of 80 pitfall traps per field. Pitfall traps set up inside the OTCs were located on the 25 cm margin around the plot (see also in Experimental design). Pitfall traps consisted in a 330 ml plastic cup, about 12 cm deep and 8 cm in diameter at the top, filled with cars' cooling liquid at 20% ethylene glycol to which we added few drops of soap to break water tension. Pitfall traps were covered, using small iron sticks, with a plastic dish raised from the opening of the trap and letting it free of access. The dish protects the trap from eventual rain and avoids its overflow. Specimens collected were stored in ethanol (96%). For the analyses, the data from the four pitfalls of each plot were merged into one single sample giving a total of 10 replicates per treatment: 10 controls and 10 OTCs per field. Arthropod sampling was performed during the winter and summer 2020 using pitfall traps set for 14 days, with a single exception of Field B in summer for which traps were available 13 days. In this case, the 14th day arthropod abundance was extrapolated from the other days. Species richness was not extrapolated.
All arthropods sampled were sorted and identified to species level, when possible, for the following target groups: Arachnida (Araneae, Opiliones, Pseudoscorpiones), Diplopoda, Chilopoda and Insecta (excluding Diptera, Hymenoptera - but including Formicidae - and Lepidoptera). Unidentified specimens were assigned to a morphospecies code. Initial sorting and identification were performed by the first author (SW) and students acting as parataxonomists (see list in Acknowledgements) and then by an expert taxonomist (PAVB). The nomenclature and colonisation status of the species follows the recent checklist of the Azorean arthropods (
In intensive pastures of Terceira, exotic arthropods are usually predominant and the abundance of native and/or endemic species are reduced due to the high level of disturbance of the land (
We combined the catch data from the four traps present in each plot. In cases where a trap was damaged (not more than one per sampling event) and data were lost, theoretical abundances were estimated by extrapolating from the data from the other three traps. In addition, when traps were only operational for 13 days, we extended the sampling period to 14 days by extrapolating arthropod abundances.
In both cases, if a trap were damaged or the sampling period were shortened by one day, the species richness was considered to be the same. Only arthropod abundances were extrapolated.
Given the relatively low distances between experimental plots, we could not rule out the possibility of spatial autocorrelation amongst samples. As the precise coordinates of the experimental units were unknown, we established an artificial grid system at each site, using the measured distances between plots and the site coordinates (see above) serving as the reference point for the centre of the initial plot located in the top left corner of the grid. These calculated coordinates for the centre of each plot were then utilised to calculate the Moran's I values as a means of testing for spatial autocorrelation. Since our samples were, indeed, found to be spatially autocorrelated and they were also obtained through a repeated sampling protocol of the same sites, we incorporated both temporal and spatial autocorrelation into our model-building process and employed generalised linear mixed models (GLMMs) with multivariate normal random effects with Penalised Quasi-Likelihood, using the glmmPQL() function from the MASS package (
As response variables, we calculated the total activity-densities for each sampling event (i.e. the pooled number of arthropods from the four traps in summer or winter), as well as the first four Hill numbers (q = 0-3). Hill numbers (
We included treatment as a fixed variable, sampling season as a random variable and generated a correlation structure from the coordinates of the sampling plots to account for spatial autocorrelation. Count data were analysed using a Quasi-Poisson distribution, whilst for the Hill numbers, a Gaussian distribution (with a log link) was used. The same modelling approach was used for all captured arthropods and spiders and beetles separately.
Partial distance-based redundancy analysis (db-RDA,
We also calculated beta diversity using the Jaccard Index to test the homogeneity in species composition between plots and seasons.
Data are available in
Overall, we collected 41,351 specimens belonging to four classes, 15 orders, 60 families and 171 morphospecies. Of these, 34 taxa were only identified at order, family or genus level, resulting in 137 taxa with scientific species names associated (n = 38,918) (from now on “species”). Abundances were generally lower in winter than in summer, while no clear differences were present in terms of species richness (Fig.
Introduced species (including those with indeterminate colonisation status, but still likely being exotic species (n = 7622)) represented 71% (n = 29664 specimens) of the total abundance and 75% (129 species) of the total richness; native non-endemic species represented 28% (n = 11608 specimens) of the total abundance and 19% (33 species) of the total richness; endemic species represented 0.2% (n = 79 specimens) of the total abundance and 1% (one species) of the total richness.
The two most diverse and abundant groups were spiders (Arachnida, Araneae) and beetles (Insecta, Coleoptera).
Overall, the omnivorous ground beetle Pseudoophonus rufipes (De Geer, 1774) (Coleoptera, Carabidae) dominated the samples and accounted for 17% of the total arthropod abundance. Besides the overall dominance, this species also dominated the summer samples, but the Ocypus olens (Müller, 1764) (Coleoptera, Staphylinidae) predatory rove beetle became dominant in the winter samples.
Oedothorax fuscus (Blackwall, 1834) (Araneae, Linyphiidae) was the dominant spider, representing 5% of the overall arthropod abundance. It was also the most abundant spider species in summer samples, whilst the winter samples were dominated by Erigone dentipalpis (Wider, 1834) (Araneae, Linyphiidae).
Of the 20 most common species, four are considered native (Leiobunum blackwalli, Tetramorium caespitum, Hypoponera eduardi, Homalenotus coriaceus), one of undetermined origin (Lithobius sp.) and the other fifteen as introduced in the Azores.
Although not significantly, the structure of the most dominant species varied slightly with elevation and, therefore, with the type of field. In the low altitude field (field A), the ground-beetle Notiophilus quadripunctatus Dejean, 1826 (Coleoptera, Carabidae) dominated the winter samples (n = 464, 14%) and the European earwig Forficula auricularia Linnaeus, 1758 (Dermaptera) the summer samples (n = 3177, 24%); at the intermediate altitude field (field B), the rove beetle Ocypus olens (Müller, 1764) (n = 579, 25%) dominated the winter samples and the ground beetle Pseudoophonus rufipes (De Geer, 1774) (n = 5822, 61%) the summer samples; and in the upper altitude field (field C), the rove beetle Amischa analis (Gravenhorst, 1802) (Coleoptera, Staphylinidae) was the most abundant species during winter (n = 211, 14%), while the harvestman Leiobunum blackwalli (Arachnida, Opiliones) (n = 3882, 33%) was dominant in summer.
According to the fitted GLMMs, the effect of OTCs treatment on arthropods abundance was significant (t = -4.88, p < 0.001), with a decrease in abundance in the OTC treatment compared to the control plots. The variance of the random intercepts was 0.62 (SD = 0.78) for the season and 43.90 (SD = 6.63) for the residual. However, the effect of OTCs treatment on arthropod richness (which also correspond to the Hill number, q = 0) was not significant (t = 0.34, p = 0.73). The variance of the random intercepts was 0.02 (SD = 0.15) for the season and 44.79 (SD = 6.69) for the residual. Fig.
Heatmap showing the correlation between abundances and samples of the twenty most common species in all sites for different seasons. The colours and the corresponding values of the heatmap are logarithmic numbers of the relative species abundance. The coloured bar in the legend has been converted back to species abundance counts. The species abundance counts indicate the abundance differences between the control plots and the OTCs. Blue colours tend to indicate a lower abundance inside the OTCs, while reddish colours indicate higher abundances inside the OTCs. A, B and C correspond to the three pastures followed by the sampling season. On the heatmap, species appear as morphospecies (MF). From left to right, they correspond to the following: MF74 Pseudoophonus rufipes (Coleoptera); MF6 Leiobunum blackwalli (Opiliones); MF56 Forficula auricularia (Dermaptera); MF F6 Tetramorium caespitum (Hymenoptera); MF 264 Anotylus nitidifrons (Coleoptera); MF 233 Oedothorax fuscus (Araneae); MF 262 Rugilus orbiculatus (Coleoptera); MF 32 Pterostichus vernalis (Coleoptera); MF F11 Solenopsis sp. (Hymenoptera); MF 246 Erigone dentipalpis (Araneae); MF 9 Ommatoiulus moreleti (Julida); MF 88 Ocypus olens (Coleoptera); MF F10 Hypoponera sp. (Hymenoptera); MF 37 Polydesmus coriaceus (Polydesmida); MF 1006 Lithobius sp. (Lithobiomorpha); MF 52 Cordalia obscura (Coleoptera); MF 66 Amischa analis (Coleoptera); MF F2 Hypoponera eduardi (Hymenoptera); MF 1620 Notiophilus quadripunctatus (Coleoptera); MF 33 Homalenotus coriaceus (Opiliones).
Dissimilarities between plots (Fig.
Heatmaps of the dissimilarities from the pairwise beta diversity analyses with using a Jaccard index a) Field A in summer, b) Field A in winter, c) Field B in summer, d) Field B in winter, e), Field C in summer, f) Field C in winter. Numbers 1 to 10 correspond to the 10 Control plots and 11 to 20 correspond to the 10 OTCs. Colour scale ranging from light to dark blue indicates increasing levels of dissimilarity. On the right side of the heatmap, the legend colour shows the dissimilarity values and the corresponding colours.
Those differences between control and OTCs were confirmed by the db-RDA (Fig.
Partial distance-based redundancy analysis. Coloured hulls represent the ordination space in which all samples are included and ellipses represent areas in which 75% of the samples are included. Green colour (C) corresponds to control and yellow colour (T) corresponds to the OTC treatment. Species most responsible for differences between treatments are marked: MF33 Homalenotus coriaceus (Simon, 1879); MF51 Paranchus albipes (Fabricius, 1796); MF52 Cordalia obscura (Gravenhorst, 1802); MF66 Amischa analis (Gravenhorst, 1802); MF262 Rugilus orbiculatus (Paykull, 1789); MF264 Anotylus nitidifrons (Wollaston, 1871).
When GLMMs were applied to a subset of the data containing beetles only, the results indicated a significant negative effect of OTC treatment on both the beetles’ abundance (estimate = -0.36, SE = 0.07, t = -5.39, p < 0.001) and species richness (estimate = -0.102, SE = 0.039, t = -2.619, p = 0.01). The variance components showed that the effect of the season accounted for a small, but significant proportion of the variance of beetle abundance (0.35, SE = 0.12), while the variance components of the beetle species richness GLMM highlighted a significant seasonal variation in beetle species richness (variance < 0.001, SD < 0.001). This indicates that there was a significant seasonal variability both in beetles’ richness and abundance.
For spiders, the abundance was significantly lower in OTC treatments (estimate = -0.23, SE = 0.11, t = -2.10, p < 0.001). On the other hand, OTCs had a significantly positive effect on spider richness (estimate = 0.11, SE = 0.04, t = 3.03, p < 0.001).
The analysis of the Hill number series (Table
Results of the t-value extracted from the glmmPQL in order to compare Hill Number values considering all arthropods, beetles and spiders. Hill number q1 represents the exponential of the Shannon entropy index, whilst q2 and q3 correspond to the inverse Simpson index and the inverse Berger-Parker index, respectively. t-values indicate the trends (negative or positive) inside the OTCs.
All arthropods | Beetles | Spiders | ||||
t-value | p-value | t-value | p-value | t-value | p-value | |
q1 | -0.069 | 0.945 | -1.893 | 0.061 | 3.226 | 0.002 |
q2 | -0.345 | 0.731 | -1.818 | 0.072 | 2.33 | 0.021 |
q3 | 0.096 | 0.923 | -1.801 | 0.074 | 1.862 | 0.065 |
For q = 2, which represents the inverse of the Simpson index, there was a significant difference between the control and OTC plots for spiders (p = 0.021). However, there was no significant difference between the control and OTC plots for beetles and when considering all arthropods.
For q = 3, which represents the inverse of the Berger-Parker index, there was no significant difference between the control and OTC plots for all arthropods, beetles or spiders.
Disentangling the impact of temperature increase on biodiversity patterns in agroecosystems constitutes a fundamental research challenge. During this short-term experiment, we simulated an increase in temperature using OTCs and tested the impacts on arthropods occurring on intensively-grazed Azorean pastures.
Most of the species we caught were introduced, commonly distributed in agroecosystems. Indeed, since highly-disturbed habitats, such as Azorean intensive pastures, mainly select for species with high dispersal capacities which can rapidly colonise ecosystems and respond to disturbances, less flexible indigenous species often have a competitive disadvantage and the presence of one or few dominant exotic species is common (
The OTCs had a significant negative effect on both the abundance and diversity of arthropods, suggesting that increased-temperature environments are less favourable for most arthropods in these pastures. Additionally, the study found that treatment effect was not uniform for all arthropods, but differed between taxa, with beetles and spiders showing different trends under the OTC treatment. Consequently, some taxa may be more vulnerable to global warming than others, which, in turn may influence the ecosystem services they deliver or the disservices they cause. Indeed,
Our results indicate that the composition of the entire arthropods community was impacted by the OTC treatment. Although the richness of the overall community was not affected, in the case of particular taxa, we noticed signs of changes that should be confirmed over much needed long-term experiments.
Indeed, some common agroecosystems species, such as Paranchus albipes, Cordalia obscura, Amischa analis, Rugilus orbiculatus, Anotylus nitidifrons and Homalenotus coriaceus, contributed disproportionately more to the observed differences than other species.
Beetles’ richness (mostly composed of carabids and rove beetles) was lower inside the OTCs and they were found to be more diverse in control plots. Although
In contrast to beetles, spiders’ richness (which belong mostly to the linyphiids) was higher inside the OTCs. This could be explained by a higher plant biomass and vegetation structural complexity inside the OTCs in our experiment (
The overall abundance, as well as that of beetles and spiders, were negatively impacted by the OTCs. Yet, the responses of different arthropod groups cannot be easily generalised. Indeed, in our study, the diversity of spider increased inside the OTCs, whilst that of beetles decreased. Thus, in Azorean pastures, spiders and beetles appear to respond differently to an increase in temperature.
Our study agrees with
Besides taxa responding differently to the heating treatment, the community composition also showed seasonal differences: we observed higher beta diversity values in winter when all species were considered in the community. This pattern might be explained by the fact that most arthropods in the Azores have a reduced abundance during the winter and tend to peak during the summer (
Species diversity is influenced not only by the number of species present in a community and their overall abundances, but also how individuals are distributed amongst those species. Although other studies, in which similar taxa were monitored as our experiment, found that certain species of ground beetles, spiders and Hemiptera became superabundant and the evenness declined with the rise in temperature (
Yet, this reduction in dominance and the increase in evenness, was statistically significant for spiders only. Indeed, even though a decrease in beetle abundance was observed with the GLMMs, Hill number analysis surprisingly did not reveal statistical differences and neither it did when all arthropods were considered. Other taxa not analysed here separately or differences between species’ ecology could also play a role in masking the trends.
Indeed, as our results showed, responses to increased temperature can be variable from one taxonomic group to the other and from one species to the other. Undoubtedly, species balance between their responses to higher temperature in the altered environment, their optimum thermal conditions and resource (e.g. food or habitat) availability and this balance highly depends on species’ traits.
This can be particularly important with species of great economic importance (e.g. pests or natural enemies). For example, in the context of increased temperature,
Additionally, since significant changes in species composition over a prolonged period can increase the probability of altered ecosystem functions (
Although our experiment was successful to predict some impacts of climate change on Azorean arthropods communities, some limitations may apply. The OTCs seems to have an indirect effect on the arthropod communities: they had an effect on the vegetation structure, particularly by increasing plant biomass (unpublished data), which may affect our results. These effects, however, need to be confirmed with further investigations. Moreover,
Our results suggest that the simulated warming had a significant impact on arthropod communities in the study area, by affecting their species richness, evenness and dominance structure. However, the impact varies depending on the arthropod group or even from species to species.
Although our study provides some important insights into the impact of increased temperature on Azorean pasture arthropods, more research is needed to allow a deeper insight. For instance, the comparison of this result with a simulated increase in temperature along an altitudinal gradient, as well as a long-term study, could help to untangle the impacts of increased temperatures in varying environments and on species with different cold adaptations. In addition, more studies on the ecology and functional traits of selected key species in Azorean pastures could help to predict general arthropod population trends for the future.
We would like to thank Virginia Pires for allowing us to use pastures A and B. We would also like to thank Mauro Matos, a bachelor student on an intership, for his help in the field and for his efforts in organising the samples prior to species identification by the expert taxonomist (P.A.V.B.).
This investigation was funded by the project PASTURCLIM (ACORES-01-0145-FEDER-000082), financed by FEDER in 85% and by Azorean Public funds by 15% through Operational Programme Azores 2020. All authors were also funded by FCT-UIDB/00329/2020-2024 (Thematic Line 1 – integrated ecological assessment of environmental change on biodiversity) and Azores DRCT Pluriannual Funding (M1.1.A/FUNC.UI&D/010/2021-2024). SW is currently being funded by the Ph.D. Grant DRCT - M3.1.a/F/018/2020.
Ethical review and approval by University of Azores were waived for this study since it did not involve vertebrates.
Conceptualisation, S.W., P.A.V.B. and R.B.E.; investigation, S.W., C.D.M., N.T., G.P., P.A.V.B. and R.B.E.; species identification and nomenclature revision, P.A.V.B. and S.W.; formal analysis, S.W., N.T., G.P. and P.A.V.B.; writing—original draft preparation, S.W.; writing—review and editing, S.W., C.D.M., N.T., G.P., P.A.V.B. and R.B.E.; funding acquisition, R.B.E.; methodology, S.W., N.T., P.A.V.B. and R.B.E; resources, R.B.E. and P.A.V.B.; data curation, S.W. and P.A.V.B.; and project administration and supervision R.B.E. All authors interpreted the results and contributed to the final manuscript and S.W. led the writing of the manuscript. All authors have read and agreed to the published version of the manuscript.
Diversity curves using Hill numbers for arthropod assemblages in the Fields A, B and C for both seasons, winter and summer. a) FAW: Field A Winter; b) FAS: Field A Summer; c) FBW: Field B Winter; d) FBS: Field B Summer; e) FCW: Field C Winter; f) FCS: Field C Summer. q orders are shown on the x axis, q0 = species richness; q1 = exponential Shannon diversity index; q2 = inverse Simpson diversity; q3 = inverse Berger-Parker diversity and their corresponding value on the y axis. Blue curves correspond to the control plots and green dotted curves to the OTCs plots.
Diversity curves using Hill numbers for beetle assemblages in the Fields A, B and C for both seasons, winter and summer. a) FAW: Field A Winter; b) FAS: Field A Summer; c) FBW: Field B Winter; d) FBS: Field B Summer; e) FCW: Field C Winter; f) FCS: Field C Summer. q orders are shown on the x axis, q0 = species richness; q1 = exponential Shannon diversity index; q2 = inverse Simpson diversity; q3 = inverse Berger-Parker diversity and their corresponding value on the y axis. Blue curves correspond to the control plots and green dotted curves to the OTCs plots.
Diversity curves using Hill numbers for spider assemblages in the Fields A, B and C for both seasons, winter and summer. a) FAW: Field A Winter; b) FAS: Field A Summer; c) FBW: Field B Winter; d) FBS: Field B Summer; e) FCW: Field C Winter; f) FCS: Field C Summer. q orders are shown on the x axis, q0 = species richness; q1 = exponential Shannon diversity index; q2 = inverse Simpson diversity; q3 = inverse Berger-Parker diversity and their corresponding value on the y axis. Blue curves correspond to the control plots and green dotted curves to the OTCs plots.