Research Article |
Corresponding author: Stênio Ítalo Araújo Foerster ( stenio.foerster@ut.ee ) Academic editor: Patricia Nunes-Silva
© 2020 Stênio Ítalo Araújo Foerster, André Felipe de Araújo Lira, Cauê Guion de Almeida.
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:
Foerster SÍA, de Araújo Lira AF, de Almeida CG (2020) Vegetation structure as the main source of variability in scorpion assemblages at small spatial scales and further considerations for the conservation of Caatinga landscapes. Neotropical Biology and Conservation 15(4): 533-550. https://doi.org/10.3897/neotropical.15.e59000
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Even at the local scale, environmental changes due of anthropogenic actions represent a source of disturbance in terrestrial ecosystems, forcing species to respond according to their ecological plasticity. Thus, stenotopic species and those with low-dispersal ability will likely be negatively affected by landscape modifications that reduce environmental complexity. In this study, we identify and quantify the effects of biotic and abiotic factors related to habitat complexity on the variation in scorpion assemblages in terms of both species’ richness, abundance and composition across 18 transects covering Caatinga landscapes with different levels of degradation. Using ultraviolet flashlights, we sampled 269 scorpions, belonging to six species and two families. The results showed contrasting patterns of species richness and abundance that depend on the level of habitat complexity. More specifically, we reported that scorpion species richness could be predicted by the number of trees, while the coefficient of variation of the diameter at breast height of trees (cvDBH) is a predictor of scorpion abundance. These findings suggest that vegetation structure is deterministic for the maintenance of scorpion assemblages in Caatinga landscapes. In addition, the cvDBH and tree number may explain 39% and 40% of the variability observed amongst scorpion assemblages in terms of richness difference and species composition, respectively. This study provides insights concerning the development of conservation strategies, clarifying the role of habitat complexity for the preservation of low-dispersal animals in neglected environments, such as those within the Caatinga domain.
Biodiversity, environmental changes, habitat complexity, macroecology, SDTF
Species composition derives from a combination of environmental factors and historical events attributed to a given area (
Our ability to determine the impact of environmental factors on species composition varies depending upon spatial scale. For instance, if ecological inferences are examined at small spatial scales, we expect that dispersal limitations would have a minor effect (if any) over the variation in species composition. In this scenario, individuals could have access to the resources available within a given area, meaning that space would act as proxy for dispersal limitation (
In this study, we aimed to measure and disentangle community parameters (species composition, α-diversity and β-diversity components) of scorpion assemblages in Caatinga environments at small spatial scales. First, we explored the potential responses of scorpion assemblages to environmental features related to habitat complexity, identifying and testing the predictors of species richness and abundance, as well as the environmental sources of similarity in species composition. Second, we explored and disentangled the patterns of β-diversity to reveal the relative contribution of species replacement and richness, as well as their environmental determinants. Third, we quantified the local contributions to the estimated β-diversity across areas of Caatinga with different levels of degradation and tested their potential association with species richness to investigate if ecological uniqueness (sensu
Fieldwork was conducted in three areas of Caatinga vegetation with different levels of degradation in the Municipality of Serra Talhada (07°58'53.32"S, 38°17'21.21"W), State of Pernambuco, Brazil. The Parque Estadual Mata da Pimenteira (Pimenteira, 07°54'0.25"S, 38°18'0.58"W) is the most preserved area we sampled in terms of vegetation diversity (Suppl. material
All transects were sampled in March 2015 and September 2016 for five consecutive days each month (2–6 Mar 2015 / 1–5 Sep 2016). Scorpions were collected at night, by three collectors who randomly walked each transect for 1 h using ultraviolet flashlights to detect scorpions because they glow a bright cyan-green under ultraviolet light (
Sampling efficiency was estimated separately for each area (Pimenteira, Pollinator Trail and Saco Road) using rarefaction/extrapolation curves, based on the estimator of species richness described in
The relative contribution of species replacement and richness difference to the overall β-diversity were accessed using the ‘adespatial’ R package taking the community matrix (sites × species) as input and applying the quantitative form of the Podani-family decomposition of Sørensen dissimilarity (
A total of 269 scorpions were collected, comprising six species: Bothriurus asper Pocock, 1893, Bothriurus rochai Mello-Leitão, 1932, Jaguajir agamemnom (C.L. Koch, 1839), Jaguajir rochae (Borelli, 1910), Physoctonus debilis (C.L. Koch, 1841) and Tityus stigmurus (Thorell, 1876). The most abundant species were J. rochae (n = 91), P. debilis (n = 84) and B. rochai (n = 73). All species were present in Pimenteira, of which, J. agamemnom and T. stigmurus occurred only in this location (Table
Species composition and absolute number of scorpion species collected at Pimenteira, Pollinator Trail and Saco Road (Pernambuco, Brazil). Specimens were collected in March 2015 and September 2016, during the rainy (R) and dry (D) season, respectively. The sample effort resulted in the collection of 269 specimens.
Species | Pimenteira | Pollinator Trail | Saco Road | ||||||
---|---|---|---|---|---|---|---|---|---|
D | R | Total | D | R | Total | D | R | Total | |
Bothriurus asper Pocock, 1893 | 1 | 3 | 4 | 2 | 2 | 4 | 2 | 3 | 5 |
Bothriurus rochai Mello-Leitão, 1932 | 14 | 39 | 53 | 1 | 2 | 3 | 8 | 9 | 17 |
Jaguajir agamemnom (C.L. Koch, 1839) | 2 | 0 | 2 | 0 | 0 | 0 | 0 | 0 | 0 |
Jaguajir rochae (Borelli, 1910) | 19 | 44 | 63 | 7 | 12 | 19 | 5 | 4 | 9 |
Physoctonus debilis (C.L Koch, 1841) | 64 | 4 | 68 | 14 | 2 | 16 | 0 | 0 | 0 |
Tityus stigmurus (Thorell, 1876) | 4 | 2 | 6 | 0 | 0 | 0 | 0 | 0 | 0 |
Total | 104 | 92 | 196 | 24 | 18 | 42 | 15 | 16 | 31 |
Species rarefaction/extrapolation curves showing the sampling efficiency of scorpions collected at Pimenteira, Saco Road and the Pollinator Trail (Pernambuco, Brazil). Solid lines represent the species richness observed from the number of individuals collected in each site, while the dashed line is a prediction (extrapolation) of the species richness if the sampling effort were multiplied by two. Grey shades around the estimated sampling curves correspond to their 95% confidence interval.
Correlation structures amongst species abundance and environmental predictors measured at Pimenteira, Saco Road and the Pollinator Trail (Pernambuco, Brazil), as summarised by two PCA axes that account for 70.1% of the total variation within the dataset (A). Environmental predictors are temperature (temp), relative humidity of the soil (ur), amount of debris (debr), number of trees (trees) and the coefficient of variation of their diameter at breast height (cvDBH); species abbreviation can be interpreted from Table
Generalised linear mixed-effects models detected significant responses of scorpion assemblages to the vegetation structure observed in each transect: the number of trees had a positive effect upon species richness (estimate ± SE = 0.23 ± 0.1; z = 2.34; p = 0.02, Fig.
Effect plot depicting the relationship between scorpion richness and the number of trees (A) and scorpion abundance with the DBH of trees measured at Pimenteira, Saco Road and the Pollinator Trail (Pernambuco, Brazil) (B); grey shades represent the 95% confidence intervals around the predictor values obtained from the generalised linear mixed-effects models. Numerical differences in the number (C) and DBH of trees (D) amongst sampling localities are also presented. Species composition varies as a function of temperature differences (see Results) and the thermal profile of each sampling site is summarised in boxplot panel (E). The linear relationship between species richness and local contribution to β-diversity is illustrated by the output of a Pearson correlation (F), in which the 95% confidence interval is represented by the grey shade.
The decomposition of the total β-diversity (βtotal = 0.30) computed for the entire region (i.e. pooling the data from all sampling localities) revealed the large contribution of richness difference (80%) over species replacement amongst transects (20%). Species replacement could be explained only by temperature (dbRDA: F(1) = 1.53, p = 0.01; R2adj = 0.03). Pimenteira was the most variable site in terms of soil temperature differences (Fig.
Absolute number of species and individuals collected from scorpion assemblages sampled at Pimenteira, Pollinator Trail and Saco Road (Pernambuco, Brazil). Scorpions were collected across 18 straight-line transects of 30 m × 10 m (six transects in each area). Geographical coordinates (longitude, latitude) were provided for each transect, as well as their local contributions to β-diversity (LCBD).
Transect | Site | Longitude and Latitude | Number of species | Number of individuals | LCBD |
1 | Pimenteira | -7.9065, -38.3002 | 3 | 36 | 0.0290 |
2 | Pimenteira | -7.9054, -38.3003 | 3 | 40 | 0.0165 |
3 | Pimenteira | -7.9045, -38.3004 | 3 | 26 | 0.0178 |
4 | Pimenteira | -7.9035, -38.3005 | 5 | 34 | 0.0142 |
5 | Pimenteira | -7.9027, -38.3008 | 6 | 36 | 0.0204 |
6 | Pimenteira | -7.9016, -38.3010 | 6 | 24 | 0.0210 |
7 | Pollinator Trail | -7.9566, -38.2981 | 2 | 6 | 0.0669 |
8 | Pollinator Trail | -7.9558, -38.2986 | 2 | 8 | 0.0750 |
9 | Pollinator Trail | -7.9550, -38.2992 | 4 | 13 | 0.0149 |
10 | Pollinator Trail | -7.9542, -38.2997 | 3 | 7 | 0.0670 |
11 | Pollinator Trail | -7.9534, -38.3002 | 3 | 4 | 0.0133 |
12 | Pollinator Trail | -7.9526, -38.3070 | 2 | 4 | 0.0635 |
13 | Saco Road | -7.9510, -38.2934 | 1 | 1 | 0.1569 |
14 | Saco Road | -7.9507, -38.2943 | 1 | 2 | 0.1094 |
15 | Saco Road | -7.9505, -38.2951 | 3 | 4 | 0.0632 |
16 | Saco Road | -7.9502, -38.2962 | 3 | 9 | 0.0516 |
17 | Saco Road | -7.9499, -38.2971 | 3 | 9 | 0.0516 |
18 | Saco Road | -7.9497, -38.2980 | 2 | 6 | 0.1478 |
In this study, we assessed the effects of environmental structure on scorpion diversity patterns in 18 linear transects covering the three Caatinga areas with different levels of environmental degradation and, thus, habitat complexity. Overall, our results indicated that heterogeneous areas of Caatinga typically support more scorpion species. These results corroborate previous assumptions that scorpion assemblages are sensitive to habitat structure, with complex habitats containing a greater number of species than monotonous landscapes (e.g.
Vegetation structure may also be involved in the maintenance of arthropod assemblages, not only by its direct and additive effects upon the availability of physical microhabitats, but also by establishing a microclimate favourable to the occurrence of a plethora of species (
The variation in species composition observed in our study may be a product of the spatial dispersal capabilities of scorpions (
The present study corroborates the assumption that changes in species composition amongst scorpion assemblages may be mediated by anthropogenic land use (e.g. roads and farming). Moreover, human-related land use modifies species composition and promotes reductions in abundance and species diversity in scorpion assemblages of Caatinga and Atlantic Rainforest environments, as already reported by previous studies (
We are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for granting a Masters and Ph.D. Scholarship to S.I.A.F. and A.F.A.L., respectively. We thank the Instituto Chico Mendes de Preservação da Biodiversidade (ICMBio) and Agência Estadual do Meio Ambiente (CPRH) for providing the pertinent documentation related to the acquisition of biological samples. Finally, we are also grateful to Valdeane Gomes da Silva and Ana Maria Tavares de Barros for technical assistance during fieldwork and to Dr. John Clarke for their contributions to the readability of this manuscript.
Table S1; Figures S1–S3
Data type: table and figures
Explanation note: Table S1. Numerical output of the principal component analysis (PCA), showing the percentual contribution of each variables for the first two axis (PC1 and PC2) of the PCA. Figure S1. General composition of microhabitat structure representing the Parque Estadual Mata da Pimenteira, located in the municipality of Serra Talhada, state of Pernambuco, northeastern Brazil. Figure S2. General composition of microhabitat structure representing the Pollinator Trail, located in the municipality of Serra Talhada, state of Pernambuco, northeastern Brazil. Figure S3. General composition of microhabitat structure representing the Saco Road, located in the municipality of Serra Talhada, state of Pernambuco, northeastern Brazil.