Research Article |
Corresponding author: María Pilar Aguirre ( mariapilar.aguirre@uclm.es ) Academic editor: Tim Gardiner
© 2018 María Pilar Aguirre, Joaquin Ortego, Pedro J. Cordero.
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:
Aguirre MP, Ortego J, Cordero PJ (2018) Influence of grazing on populations of the specialist grasshopper Mioscirtus wagneri inhabiting hypersaline habitats in La Mancha Region, Central Spain. Journal of Orthoptera Research 27(1): 75-81. https://doi.org/10.3897/jor.27.21064
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Grazing is an influential land use that has introduced profound changes in worldwide landscapes, ecosystems and their species. In this paper, we analysed the influence of grazing on the presence and abundance of the endangered Mioscirtus wagneri, a monophagous grasshopper inhabiting inland hypersaline ecosystems in Spain and showing a marked spatial and genetic fragmentation. Using count transects, we analyzed the presence and abundance of this grasshopper in relation to specific vegetation cover and the abundance of goat and sheep droppings, considering this variable as a surrogate of livestock activity and grazing impact. We found that both the presence and abundance of M. wagneri were positively related to the cover of its host plant Suaeda vera and negatively associated with the abundance of droppings. We conclude that dropping abundance is a useful parameter to assess livestock impact and evaluate habitat quality and the conservation status of M. wagneri and many other singular species of macroinvertebrates inhabiting inland hypersaline ecosystems. We highly recommend the use of electric shepherd fencing around all sensitive and protected areas where inland hypersaline ecosystems are present in order to deter livestock. We also suggest intensive educational campaigns for farmers and shepherds, revealing the ecological importance of these singular and unique habitats for rare and exclusive species like M. wagneri and many other coexisting plants and invertebrates.
Castilla-La Mancha, conservation, grazing management, inland hypersaline ecosystems, livestock droppings, Suaeda vera
Historical and current grazing activities are an important influence on the landscape and, thus, on plant and animal community composition (
To test the impact of grazing on grasshopper abundance, we focused on the populations of a specialist species, Mioscirtus wagneri (Kittary, 1859) (Orthoptera: Acrididae) inhabiting continental hypersaline habitats both around hypersaline lagoons and in salted ground prairies of the plant association Suadetum brevifoliae (
Here, we aim to provide information on threats related to livestock activity on M. wagneri and its sensitive and exclusive hypersaline habitat. The aim of this study is to determine, 1) the association of M. wagneri with its host plant (S. vera, alkali seepweed) and 2) how grazing activity is related to the presence and abundance of this grasshopper in two localities, including grazed and ungrazed plots around hypersaline lagoons of La Mancha Region (Central Spain). To attain this, we analysed the relationship between the abundance and presence of M. wagneri obtained from count transects and the cover of different species of plants, the type of soil, and the abundance of livestock droppings, used as a surrogate of the intensity of livestock activity.
Study area.—The study area includes two inland salted lagoons in the center of Iberian Peninsula: Peña Hueca (3°20’29”W, 39°30’50”N) and Tirez (3°21’27”W, 39°32’21”N) (Villacañas, Toledo Province, Central Spain) (Fig.
The grasshopper.—The study species is Mioscirtus wagneri, a monophagous and specialist grasshopper with a disjunct distribution and high genetic fragmentation of its populations (
Transects and variables.—To measure M. wagneri presence/abundance, plant species and soil type cover, we used transects in areas with different influences from grazing but within the local distribution of the grasshopper. Transects were 20 m in length, and 0.5 m on each side of the observer were surveyed (a total area of 20 × 1 m per transect = 20 m2). On transects we collected data on M. wagneri presence and abundance, soil type, cover and species of plants and number of droppings of sheep and goats. Transects were chosen taking into account the presence/absence of sheep and goat droppings and trying to include areas that have been differentially impacted by grazing. Transects were chosen at random in these areas although we tried to include those with homogeneous vegetation structure along their entire length. Grasshoppers were counted excluding possible repetitions of individuals. Transects were walked as slowly as necessary (2 km/hr) to accurately record the presence and abundance of grasshoppers. Finally, we took pictures of each transect to check plant and soil type cover. As we previously knew the orthopteran communities in these hypersaline areas, and because of the low number of grasshoppers living in salted grounds, we only took into account censuses of M. wagneri, discarding other species for analyses. The area and orthopteran communities have been studied since 2005 (P.J. Cordero unpublished). Further, M. wagneri is easy to identify de visu due to its external appearance, color and hind wing markings. Only Aiolopus strepens could be confused with M. wagneri beyond a certain distance, but we always took into account this possibility and misidentification was minimal. Capture by hand or netting was unnecessary for identification. Our census of Orthoptera was repeatable and efficient, particularly because the species is well known in the orthopteran community and is easily identifiable (e.g.
We carried out 65 transects in Tirez and 100 transects in Peña Hueca lagoons between 10 and 17 h, during August 2009, the month in which M. wagneri is present with 100% adult forms (
Three percentages of bare soil were considered: brown clay soil not affected by high salt concentration (CLAYED), hypersaline white/grey soil (SALT) and plowed land (PLOWED). Other variables included the percentage cover of the main plant associations in the area. SEEPWEED: formed by the community Suaedetum brevifoliae described above, with S. vera as its most abundant plant species. This small bush is scattered and rarely exceeded 70% ground cover in the study area. It is often associated with other smaller herbaceous species such as Hordeum marinum, Puccinella fasciculata and, sometimes, Frankenia thymifolia and F. pulverulenta. HALOPHYTES: heterogeneous grassland associations belonging to halophilic communities, excluding S. vera, with plants such as Sarcocornia perennis, Salicornia ramosissima, Arthrocnemum coraloides, Spergularia media, Limonium spp., Plantago maritima, Suaeda maritima and some grasses such as Hordeum marinum, Polypogon maritimus, Aeluropus littoralis or Puccinellia fasciculata (maximum vegetation cover = 79%). SALSOLA: Salsola vermiculata association. The distribution of this plant species is similar to that presented by S. vera, however the salinity of the soil may be lower, interspersed with various ruderal species such as Scolymus sp., Bromus sp., Centaurea sp., Chamaemelum sp., Frankenia sp., etc. (maximum vegetation cover = 80%). ESPARTO: includes formations of Lygeum spartum (esparto grass) characterized by dense cover when it is present as the only species (maximum cover = 100%). The accompanying species is usually Limonium sp. in moist areas. WHEATGRASS: mainly composed of Thinopyrum curvifolius (wheatgrass), of size and structural characteristics similar to ESPARTO, with high ground covering, often with Juncus sp. in small amounts (maximum vegetation cover = 80%). HERBACEOUS: several non-halophile ruderal plants including Phragmites sp. among others (maximum vegetation cover = 85%). STUBBLE: mown fields of wheat and barley, very close to halophile vegetation plots and rarely including any other ruderal plant species (maximum vegetation cover = 100%). DROPPINGS: number of individual cylindrical droppings of ovine-goat livestock. We assigned large clusters of faeces composed of a certain number of dropping units (5 to 10 each) according to their size. We used this variable as a surrogate of livestock influence/presence (i.e. grazing impact) and, thus, it is related to cumulative livestock presence in the area (range of droppings abundance between 0 and 7/m2). For analysis, we also recorded the hour (HOUR) when each transect was performed.
Statistical analyses.—We performed a forward stepwise logistic regression in order to analyze the presence of M. wagneri (PRESENCE, dependent or response variable) in relation to the cover of the different types of plant species (SEEWEED, HALOPHYTES, SALSOLA, ESPARTO, WHEATGRASS, HERBACEOUS, and STUBBLE), cover of the different types of bare soil (CLAYED, SALT, and PLOWED) and the number of droppings per transect (DROPPINGS). We also included in the model the hour (HOUR) and the lagoon (LAGOON) of sampling transects. To analyse the abundance of M. wagneri (ABUNDANCE), we performed a forward stepwise multiple regression considering the same independent variables as indicated above. Analyses were performed using SPSS v11 (
The average abundance of M. wagneri in transects with a presence of the species was 0.3 individuals/m2 (range 0.05-1.3 individuals/m2). We found that the presence of M. wagneri (PRESENCE) was positively related to the cover of S. vera (SEEPWEED) (Wald = 40.65, df = 1, P < 0.0001; Fig.
Results of the forward stepwise logistic regression analysis for presence of Mioscirtus wagneri (PRESENCE) in relation to the different explanatory variables analyzed.
Estimator ± S.E. | Wald | P | |
---|---|---|---|
Variables included | |||
Constant | -3.29 ±0.49 | 45.55 | <0.001 |
SEEPWEED | 0.17 ±0.30 | 40.65 | <0.001 |
DROPPINGS | -0.30 ±0.11 | 8.02 | <0.005 |
Variables excluded | |||
HALOPHITES | 2.26 | 0.100 | |
SALSOLA | 2.56 | 0.110 | |
ESPARTO | 0.00 | 0.972 | |
WEATGRASS | 0.00 | 0.996 | |
HERBACEUS | 0.74 | 0.390 | |
CLAYED | 3.65 | 0.056 | |
PLOWED | 0.00 | 0.999 | |
SALT | 1.65 | 0.199 | |
STUBBLE | 0.00 | 0.999 | |
HOUR | 1.47 | 0.225 | |
LAGOON | 0.01 | 0.801 |
Relationship between probability of presence of Mioscirtus wagneri in the transects (PRESENCE) and A. Cover (%) of Suaeda vera (SEEPWEED) for extreme values of livestock droppings per square meter (DROPPINGS), and B. Livestock droppings per square meter (DROPPINGS) for extreme values of cover (%) of S. vera (SEEPWEED).
Results of the forward stepwise multiple regression analysis for number of Mioscirtus wagneri/m2 (ABUNDANCE) in relation to the different explanatory variables analyzed.
Estimator ± S.E. | F | P | |
Variables included | |||
Constant | -4.56 ±1.67 | 7.46 | <0.007 |
SEEPWEED | 0.15 ±0.13 | 147.67 | <0.001 |
DROPPINGS | -0.40 ±0.11 | 13.55 | <0.001 |
HOUR | 9.80 ±3.32 | 8.64 | <0.004 |
Variables excluded | |||
HALOPHITES | 0.04 | 0.823 | |
SALSOLA | 0.08 | 0.782 | |
ESPARTO | 0.89 | 0.347 | |
WEATGRASS | 0.05 | 0.817 | |
HERBACEUS | 0.17 | 0.670 | |
CLAYED | 2.67 | 0.104 | |
PLOWED | 0.12 | 0.729 | |
SALT | 0.00 | 0.988 | |
STUBBLE | 0.14 | 0.705 | |
LAGOON | 0.69 | 0.406 |
Our results show the dependence of M. wagneri on alkali seepweed formations as expected from a previous observational study (
Irrespective of the mechanisms involved in the negative relationship between the abundance of droppings and the presence and abundance of M. wagneri, our analyses indicate that we can use information on dropping counts as a surrogate of habitat quality for M. wagneri. Dropping counts seem to be a measurable and straightforward tool for determining the conservation status and for implementing management measures for preserving the populations of M. wagneri and the sensitive hypersaline habitat where this grasshopper occurs. Dropping counts could help to improve management decisions related to compliance with legislation regarding livestock activities and habitat and species conservation. The estimate of droppings is even more important in our study if we consider that inland hypersaline habitats of M. wagneri are, by extension, shared by many macroinvertebrate species of great conservation interest within territories of high conservation concern. These include rare and fragmented taxa adapted to salinity, endemics dependent on salted soils, halophilous vegetation, or terrestrial steppic macroinvertebrates that find refuge from agriculture in these hypersaline ecosystems (
We highly recommend the use of electric shepherd fencing around all sensitive and protected areas where inland hypersaline ecosystems are present in order to deter livestock. We also recommend intensive educational campaigns for farm owners and shepherds, showing the ecological importance of these singular and unique habitats for rare and exclusive species of plants and invertebrates.
Dragan Chobanov, Paolo Fontana and Tim Gardiner provided valuable comments on an earlier draft of this manuscript. This work received financial support from grants: POII09-0198-8057, PCI08-0130-3954 and POII10-0197-0167 (Junta de Comunidades de Castilla-La Mancha and European Social Fund), CGL2011-25053 and CGL2016-8742-R (Spanish Dirección General de Investigación y Gestión del Plan Nacional I+D+i and European Social Fund). JO was supported by a Ramón y Cajal (RYC-2013-12501) research fellowship.