Research Article |
Corresponding author: Jorge Luis Becerra-López ( biologo.jlbl@gmail.com ) Academic editor: Franco Andreone
© 2017 Jorge Luis Becerra-López, Aurelio Ramírez-Bautista, Ulises Romero-Méndez, Numa P. Pavón, Gerardo Sánchez-Rojas.
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:
Becerra-López JL, Ramírez-Bautista A, Romero-Méndez U, Pavón NP, Sánchez-Rojas G (2017) Effect of climate change on halophytic grasslands loss and its impact in the viability of Gopherus flavomarginatus. Nature Conservation 21: 39-55. https://doi.org/10.3897/natureconservation.21.13614
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The decrease of the habitat is one of the main factors that affect the survival of G. flavomarginatus. This study assesses the halophytic grasslands loss over a period of 30 years in the distribution area of the Bolson tortoise and the effects of climate change on the habitat suitability of these grasslands and its possible impact on this tortoise. Grassland loss was assessed by an analysis of symmetric differences and the habitat suitability model was carried out by the method of overlapping layers raster. Our results showed a grassland loss of 63.7%; however, our current habitat suitability model points out that much of the grassland loss has occurred where the environmental conditions are suitable. These results suggest that anthropic activity is a main factor in the habitat disturbance in the study area. Likewise, the models for years 2050 and 2070 under the criteria RCP 2.6, RCP 4.5, RCP 6.0, suggest that anthropic activity will continue be the main cause of the grassland loss. Therefore, considering the association between the Bolson tortoise and grassland halophyte Hilaria mutica, which comprises around 60% of its diet, the viability of the Bolson tortoise depends largely on strategies aimed at protecting the soil that allow the presence of this grassland.
Gopherus flavomarginatus; spatial distribution; climate change; halophytic grasslands
Climate influences plant and animal distributions due to their requirements related to temperature and humidity (
Climate change and change of land use are two of the factors that most affect natural systems (
To assess the effect of the climate change on species distribution, ecological niche modeling has been used employing different environmental variables and mathematical algorithms that try to simulate the climate niche of a species and represent it geographically on a map (
Chihuahuan Desert grasslands provide important resources as habitats and food for sustaining a very rich animal diversity (
Historically, the Bolson tortoise was distributed from the southwestern USA to the center of México. However, it is currently confined to the area known as the Bolson of Mapimí (
The Chihuahuan Desert has an approximate area of 507,000 km2 and elevations from 800 to 2500 m-asl; it extends from central México northward to southern Texas, Arizona, and New México. The mean annual precipitation varies from 175 to 400 mm. The characteristic vegetation is microphyllous desert scrub, rosette desert scrub, crassicaule desert scrub, and grasslands, among others (
Sixty one records of G. flavomarginatus were identified, with these points we delimited a Minimum Convex Polygon (MCP) of 15,895.5 km2 that represents the distributional area of the Bolson tortoise. This polygon was zoned according to the densities of the geographic points using the clustering K-means method (Software CrimeStat V. 3.2, 2009).
In order to identify loss and gain areas of halophilic grasslands (1980–2013) we used a symmetric difference analysis (Software ArcMap V. 10.1;
Subsequently, within the area MCP2 were settled 232 quadrants out of 100 km2, each one. In each quadrant we added the corresponding value for each bioclimatic variable, as well as the information of presence and absence of the halophytic grasslands. In order to identify the bioclimatic variables that explain the presence and absence of the halophytic grasslands in the study area, was used an analysis of discriminant factors (canonical) under the generalized linear model. This analysis was performed using the library “MASS” (
For modeling the habitat suitability of halophytic grasslands under current climatic conditions in the Chihuahuan Desert, we used the retained bioclimatic variables in the discriminant analysis. The selected variables were annual mean temperature, mean diurnal range, minimum temperature of the coldest month, annual precipitation, and precipitation of wettest quarter, as well as substrate texture data (
The same climatic profile was used for modeling habitat suitability for the scenario of the climatic change to 2050 and 2070 in the Chihuahuan Desert. We used data as scenarios of the climatic change corresponding to the extrapolated with Beijing Climate Center Climate System Model (BCC-CSM1-1, this was chosen at random from a group of 19 climate models) for the years 2050 and 2070 under different Representative Concentration Pathways (RCP): RCP 2.6 = +2.6 W/m2, RCP 4.5 = +4.5 W/m2, RCP 6.0 = +6.0 W/m2, and RCP 8.5 = +8.5 W/m2 were used as scenarios of the climatic change. Under the scenario RCP 2.6 a minor intensity of the effects of the climate changes is expected, while with the scenario RCP 8.5 the intensity will be greater (
The emergence of new technologies and recent assumptions about socioeconomic development, as well as observations of environmental factors such as land use and land cover change have been considered in this new generation of scenarios (
For the validation of the model were used the zones with presence of halophytic grasslands in the Chihuahuan Desert reported by the Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (
To assess the climate change impact on the habitat suitability of the halophytic grasslands we obtained the percentage change for each scenario using the following formula (
% of change = [(S1 – S0)/S0]*100,
Where:
S0, is the total surface of the study area, according to the base scenario.
S1, is the total surface occupied in the study area under change conditions.
Three zones in the distribution area of G. flavomarginatus were identified, these zones were classified as “A” with 2,649.99 km2, “B” with 5,472.21 km2, and “C” with 2,657.11 km2 (Figure
The current model habitat suitability identifies the greatest part of the localities where halophytic grasslands had been reported in the Chihuahuan Desert (
Distribution of gain and loss of the halophytic grassland in an area of 32,300 km2. Black spots show populations of G. flavomarginatus; dotted lines show distribution zones “A”, “B” and “C” of the species; the black line indicates the Mapimí Biosphere Reserve; dark grey color shows the zones with gain of halophytic grassland; light grey color shows the zones of halophytic grassland loss; medium grey color shows areas with grasslands that has been maintained; the grid make reference to squares of 100 km2 in the study area.
Habitat suitability models of the halophytic grasslands projected for Chihuahuan Desert. White lines show states boundaries; black lines refer to the Mapimí Biosphere Reserve; blue lines indicate distribution zones of G. flavomarginatus.
Habitat suitability for distribution of G. flavomarginatus considering the different climatic scenarios assessed.
Habitat suitability | Zone A | Zone B | Zone C |
---|---|---|---|
Current habitat suitability | 1,087.99 km2 | 999.49 km2 | 594.04 km2 |
Habitat suitability RCP 2.6-2050 | 1,087.56 km2 | 999.48 km2 | 594.02 km2 |
Habitat suitability RCP 4.5-2050 | 1,007.85 km2 | 1,027.28 km2 | 0 km2 |
Habitat suitability RCP 6.0-2050 | 1,179.83 km2 | 1,065.37 km2 | 624.11 km2 |
Habitat suitability RCP 8.5-2050 | 143.066 km2 | 1,023.241 km2 | 0 km2 |
Habitat suitability RCP 2.6-2070 | 1,087.43 km2 | 999,46 km2 | 593.92 km2 |
Habitat suitability RCP 4.5-2070 | 1,008.61 km2 | 1,117.54 km2 | 657.39 km2 |
Habitat suitability RCP 6.0-2070 | 921.69 km2 | 999.77 km2 | 510.25 km2 |
Habitat suitability RCP 8.5-2070 | 0 km2 | 25.7 km2 | 0 km2 |
Change rate of the habitat suitability area for halophytic grassland in Chihuahuan Desert considering current and future climatic conditions (2050 and 2070) under concentrations of greenhouse gases RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5.
Current model | Model 2050 | Model 2070 | Model 2050 | Model 2070 | Model 2050 | Model 2070 | Model 2050 | Model 2070 |
---|---|---|---|---|---|---|---|---|
RCP 2.6 | RCP 4.5 | RCP 6.0 | RCP 8.5 | |||||
29,715.73 | 27,413.14 | 26,133.87 | 23,414.74 | 26,644.12 | 26,401.96 | 22,390.37 | 16,288.26 | 5,546.78 |
Change rate (%) | -7.74 | -12.05 | -21.20 | -10.33 | -11.15 | -24.65 | -45.18 | -81.33 |
The results of this study show that halophytic grassland loss in the current distribution area of G. flavomarginatus has been a continuous process, in as much as in a period of 30 years its reduction has been 63.7%, with the zone “A” being the most affected. In this context, halophytic grasslands loss for the Chihuahuan Desert has been attributed to the climatic change and to the anthropic factors (e.g., agriculture and cattle;
The current habitat suitability model of this study indicates that climatic conditions of the area that showed the highest loss of halophytic grassland inside the known distribution range of G. flavomarginatus (zone “A”) are appropriate for the presence of this grassland. Data on land use and vegetation presented by Instituto Nacional de Estadística y Geografía (
In this context, it has been documented that changes in vegetal species distribution promote that animal species also modify their behavior and distribution (
For the lizard species Uma exul and Uma paraphygas, it has been reported that their specificity on dune ecosystems and their low dispersal capacity reduce the probability of migration to places where the habitat conditions are suitable to live. These two species show very low genetic variability; therefore, it has been pointed out that these species are in critical condition because of the transformation of their habitat (
Accordingly, considering the association between Bolson tortoise and the halophytic grass H. mutica that comprises 60% of its diet (
On the other hand, expectations of climate change for years 2050 and 2070 under scenarios RCP 2.6, RCP 4.5, and RCP 6.0 show a slight decrease in habitat availability for halophytic grassland in the Chihuahuan Desert, zones A and B, however show relative stability. This suggests that fragmentation of halophytic grassland in the range of the Bolson tortoise will depend on the change in land use. Under conditions of a pessimistic scenario (RCP 8.5) change rate of the habitat suitability area for halophytic grassland in the Chihuahuan Desert for years 2050 and 2070 will be of -45.186 and -81.333%, respectively. Under this scenario the viability of the Bolson tortoise is heavily compromised.
In conclusion, viability of the Bolson tortoise will depend on the strategies of protection and the land conservation allowing for the presence of halophytic grassland composed of H. mutica. In this regard, conservation programs for the Bolson tortoise and its habitat currently are addressed mainly within the Mapimí Biosphere Reserve; however, according to the available evidence, this zone is strongly affected by anthropogenic factors. Likewise, monitoring programs of the populations and habitat conditions of the Bolson tortoise are performed in an area of 1 km2 scattered inside the Protected Natural Area (
Conceptualization: JLBL NPP URM. Formal analysis: JLBL URM. Investigation, writing and editing: JLBL URM NPP GSR ARB. Resources: JLBL URM NPP GSR ARB.
We thank to the members of the Tlahualilo, Durango, commonality and the Mapimí Biosphere Reserve administration for the logistic help to carry out this study; to Larry David Wilson and Muhammad Ehsan for reading and improving the manuscript and Mirsha Rojas Domínguez for providing the image of Gopherus flavomarginatus. Finally, we thanks two anonymous reviewers for their valuable comments on this manuscript.