Importance of positive interactions for niche space in deserts

Positive interactions among species have been described as supporters of biodiversity in resource limited or high stress ecosystems. However, the area that these species are supported is rarely quantified. In deserts, shrubs can facilitate annual plants and allow them to survive in areas that otherwise would be unhospitable, i.e. support the niche. These “islands of suitability” are created under the shrub because there is more shade, the microclimate is cooler, herbivory pressure is reduced, and many other potential mechanisms that benefit the annual plants. Imagined over a larger area, such as the Mojave Desert, this increase in landscape heterogeneity creates a wider range of conditions where an annual species can exist. Within our study we discussed the debate in literature on positive interactions and the niche of a beneficiary species in detail and propose three possible explanations.

The area the beneficiary species area inhabits increases through any one or combination of these three pathways. We found within this study that when conducting species distribution modelling of desert annual species, that the range of these species was increased with the inclusion of shrubs as a proxy for positive interactions. We also found that shrubs did not increase the range of annual species that had no previous history of being facilitated in the scientific literature. Recent advances in species distribution modelling are making it easier to include biotic interactions when modelling the niche space and range of target species. Positive interactions have been identified as important for supporting high stress ecosystems, such as deserts. Within our study we support this finding and encourage further research continue to modelling the effects of positive interactions on desert annuals. It is important to quantify the range and mechanistic pathways that shrub can facilitate annual communities to provide ecologists and local stakeholders the tools necessary when managing desert lands for conservation. 

The authors through Alessandro Filazzola

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