Although long‐standing theory suggests that biotic variables are only relevant at local scales for explaining the patterns of species' distributions, recent studies have demonstrated improvements to species distribution models (SDMs) by incorporating predictor variables informed by biotic interactions. However, some key methodological questions remain, such as which kinds of interactions are permitted to include in these models, how to incorporate the effects of multiple interacting species, and how to account for interactions that may have a temporal dependence. We addressed these questions in an effort to model the distribution of the monarch butterfly Danaus plexippus during its fall migration (September–November) through Mexico, a region with new monitoring data and uncertain range limits even for this well‐studied insect. We estimated species richness of selected nectar plants (Asclepias spp.) and roosting trees (various highland species) for use as biotic variables in our models. To account for flowering phenology, we additionally estimated nectar plant richness of flowering species per month. We evaluated three types of models: climatic variables only (abiotic), plant richness estimates only (biotic) and combined (abiotic and biotic). We selected models with AICc and additionally determined if they performed better than random on spatially withheld data. We found that the combined models accounting for phenology performed best for all three months, and better than random for discriminatory ability but not omission rate. These combined models also produced the most ecologically realistic spatial patterns, but the modeled response for nectar plant richness matched ecological predictions for November only. These results represent the first model‐based monarch distributional estimates for the Mexican migration route and should provide foundations for future conservation work. More generally, the study demonstrates the potential benefits of using SDM‐derived richness estimates and phenological information for biotic factors affecting species distributions.
Aim:We test a new species distribution modelling (SDM) framework, while comparing results to more common distribution modelling techniques. This framework allows for the combination of presence-only (PO) and presence-absence (PA) data and accounts for imperfect detection and spatial bias in presence data. The new framework tested here is based on a Poisson point process model, which allows for predictions of population size. We compared these estimates to those provided by experts on the species. Species and Location: Presence data on Baird's tapir (Tapirus bairdii) throughout its range from southern México to northern Colombia were used in this research, primarily from the years 2000 to 2016. Methods: Four SDM frameworks are compared as follows: (1) Maxent, (2) a presenceonly (PO) SDM based on a Poisson point process model (PPM), (3) a presence-absence (PA) SDM also based on a PPM and (4) an Integrated framework which combines the previous two models. Model averaging was used to produce a single set of coefficient estimates and predictive maps for each model framework. A hotspot analysis (Gi*) was used to identify habitat cores from the predicted intensity of the Integrated model framework. Results: Important variables to model the distribution of Baird's tapir included land cover, human pressure and topography. Accounting for spatial bias in the presence data affected which variables were important in the model. Maxent and the Integrated model produced predictive maps with similar patterns and were considered to be more in agreement with expert knowledge compared to the PO and PA models.Main conclusions: Total abundance as predicted by the model was higher than expert opinion on the species, but local density estimates from our model were similar to available independent assessments. We suggest that these results warrant further validation and testing through collection of independent test data, development of more precise predictor layers and improvements to the model framework.
Resumen. Los mamíferos son uno de los grupos más conspicuos de las comunidades terrestres de vertebrados y muestran una serie de características internas y externas que los han llevado a ser exitosos en casi todos los ecosistemas del mundo. El objetivo de esta revisión es actualizar el estado de conocimiento de los mamíferos de México. En México los mamíferos forman un grupo altamente diverso, ubicando al país en el tercer lugar mundial con 564 especies silvestres, alcanzando aproximadamente el 10% de la diversidad total. La descripción de las especies no ha sido homogénea a lo largo del tiempo y tuvo un mayor auge desde mediados de 1700 hasta 1950. La distribución de los mamíferos incluye todo el territorio nacional; el 77% son especies menores a 5 kg y pertenecen, principalmente, a los órdenes Rodentia, Chiroptera y Soricomorpha. Las tendencias poblacionales están poco documentadas en la mayoría de los órdenes pero, en general, los mamíferos han visto disminuidas sus poblaciones como resultado de las actividades antrópicas. La información analizada sugiere que a pesar de que el grupo de los mamíferos en México es uno de los más estudiados, continúa ofreciendo interesantes retos teóricos y de manejo.Palabras clave: mamíferos marinos, mamíferos terrestres, número de especies, talla, hábitat.
ResumenGuerrero es el cuarto estado más biodiverso en México, incluyendo 930 especies de vertebrados en su territorio. Sin embargo, ha mostrado una pérdida significativa de hábitats naturales originales. Se hace evidente la necesidad de generar información sobre los procesos involucrados en pérdida de hábitats naturales, así como identificar los impactos que tienen tales pérdidas sobre la distribución de especies. Se generaron modelos de la distribución potencial del hábitat adecuado para 47 especies, mediante la aplicación del método MaxEnt para la predicción de su distribución geográfica y se refinaron, a su vez, a modelos de la distribución actual de hábitats adecuados. Se analizó la relación entre la amplitud de la distribución potencial de hábitats adecuados y la proporción de hábitat natural remanente para cada especie, tanto a nivel estatal (Guerrero) como nacional (México), y se identificaron zonas de Guerrero necesarias para alcanzar metas fijas de conservación de las especies. Los resultados no mostraron una correlación significativa entre la amplitud de la distribución potencial de hábitats adecuados de las especies y las áreas remanentes de hábitats originales a nivel estatal o nacional. De hecho, existen diferencias significativas en las proporciones de hábitat remanente entre ambas escalas. Esto sugiere que la escala es un factor importante para establecer estrategias de conservación para las mismas especies a nivel local, regional o nacional.
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