Frontiers of Biogeography

In recent years, ecological research has suggested several mechanisms by which biodiversity might affect the risk of acquiring infectious diseases (i.e., the decoy, dilution or amplification effects), but the topic remains controversial. While many experimental studies suggest a negative relationship between biodiversity and disease, this relationship is inherently complex, and might be negative, positive or neutral depending on the geographical scale and ecological context. Here, applying a macroecological approach, we look for associations between diversity and disease by comparing the distribution of human schistosomiasis and biogeographical patterns of freshwater snail and mammal species richness in Uganda. We found that the association between estimated snail richness and human infection was best described by a negative correlation in non-spatial bi- and multivariate logistic mixed effect models. However, this association lost significance after the inclusion of a spatial component in a full geostatistical model, highlighting the importance of accounting for spatial correlation to obtain more precise parameter estimates. Furthermore, we found no significant relationships between mammal richness and schistosomiasis risk. We discuss the limitations of the data and methods used to test the decoy hypothesis for schistosomiasis, and highlight key future research directions that can facilitate more powerful tests of the decoy effect in snail-borne infections, at geographical scales that are relevant for public health and conservation.

With recent advances in biotechnology, the resurrection of recently extinct species has become a possibility, provoking a debate about the wisdom of what has become known as de-extinction. Regardless of the current feasibility and ethical controversies over de-extinction, ongoing technological advancement is likely to result in resurrected species in the near future. In our opinion, de-extinction will be followed by proposals for reintroduction into the wild. We argue that this development could be valuable for the advancement of ecological understanding and conservation.  However, the current conversations are happening in a vacuum. We therefore call for the initiation of field experiments using physiological and ecological surrogates. This type of research could shed light on the potential impacts of resurrected animals on modern ecosystems. While this research would have challenges, it could provide valuable information on th ecology of the past and better prepare scientists and wildlife managers for de-extinction.

High elevation islands elicit fascination because of their large array of endemic species and strong environmental gradients. First, I define a high elevation island according to geographic and environmental characteristics. Then, within this high elevation island framework, I address local disturbance effects on plant distribution, drivers of diversity and endemism on the island scale, and global patterns of treeline elevation and climate change. Locally, introduced herbivores have strong negative effects on the summit scrub of my model island La Palma (Canary Islands), while roads have unexpected positive effects on endemics. On the island scale, topography and climate drive diversity and endemism. Hotspots of endemicity are found in summit regions – a general pattern on high elevation islands. The global pattern of treeline elevation behaves quite differently on islands than on the mainland. A thorough literature review and climate projections suggest that climate change will profoundly affect oceanic island floras.

My goal is to investigate global patterns in the structure of interaction networks of insect herbivores and their host plants. Specifically, I seek to determine whether intensification of land use and the dominance of exotic host plant species influence the structure and robustness (i.e., resistance to co-extinctions) of interaction networks of insect herbivores and host plants. I also ask whether latitude has an influence on the structure and robustness of these interactions. I compiled 90 local plant-herbivore networks distributed worldwide, spanning different taxonomic groups of plants and insects and several herbivore guilds. My results showed that intensification of land use was associated with dominance of exotic plant species and can impoverish the species richness and taxonomic diversity of insect herbivores in the networks. Moreover, land use intensification surprisingly increases network specialization by decreasing connectance and nestedness, and increases modularity; while the increase in the proportion of exotic hosts had opposite effects. These changes in the network structure may be due to the proportionately greater loss of generalist herbivores relative to specialists. Land use intensification also decreases the robustness of plant-herbivore networks, while the proportion of exotic host plant species increases, which is an intriguing result that contradicts previous studies. Controlling for anthropic effects that can act on the networks, my results show that plant–herbivore networks are structured independently of latitude, suggesting that the factors that influence the interactions between host plants and insect herbivores are latitudinally invariant.

Nearly 20% of bird species are migratory, their seasonal movements causing a redistribution of bird diversity that radically changes avian community composition worldwide. And yet, bird migration has been largely ignored in studies of global avian biodiversity. My thesis is the first global macroecological analysis of bird migration. Using a dataset on the geographical distributions of the world’s birds, I mapped global patterns of migratory bird diversity, revealing strong spatial features. I then used these patterns to test hypotheses exploring the ecological processes driving bird distributions in space and time. From these results, I developed the first mechanistic, process-based model of bird migration at the global scale. From first principles – converting key ecological processes into a common currency of energy – this model successfully explains the global patterns previously described. My research provides a better understanding of why birds migrate and opens new research avenues on this remarkable phenomenon.

WorldClim (Hijmans et al. 2005) has been the de-facto source of basic climatological analyses for most species distribution modeling research and conservation science applications because of its global coverage and fine (<1 km) spatial resolution.  However, it has been recognized since its development that there are limitations in data-poor regions, especially with regard to the precipitation analyses.  Here we describe procedures to develop a satellite-based daytime cloudiness climatology that better reflects the variations in vegetation cover in many regions of the globe than do the WorldClim precipitation products.  Moderate Resolution Imaging Spectroradiometer (MODIS) imagery from the National Aeronautics and Space Administration (NASA) Terra and Aqua sun-synchronous satellites have recently been used to develop multi-year climatologies of cloudiness.  Several procedures exist for developing such climatologies.  We first discuss a simple procedure that uses brightness thresholds to identify clouds.  We compare these results with those from a more complex procedure: the MODIS Cloud Mask product, recently averaged into climatological products by Wilson and Jetz (2016).  We discuss advantages and limitations of both approaches.  We also speculate on further work that will be needed to improve the usefulness of these MODIS-based climatologies of cloudiness. Despite limitations of current MODIS-based climatology products, they have the potential to greatly improve our understanding of the distribution of biota across the globe.  We show examples from oceanic islands and arid coastlines in the subtropics and tropics where the MODIS products should be of special value in predicting the observed vegetation cover.  Some important applications of reliable climatologies based on MODIS imagery products will include 1) helping to restore long-degraded cloud-impacted environments; 2) improving estimations of the spatial distribution of cloud-impacted species; and 3) helping to identify areas for rapid biological assessments.  The last application can even benefit from qualitative perusal of the current MODIS climatologies.

Western Europe covered by clouds on September 1, 2012. Picture by NASA, MODIS Rapid Response System. Cropped  from http://lance-modis.eosdis.nasa.gov/wms/?zoom=4&lat=49.875&lon=21.60938 &layers=B0000FFFFT&datum1=09/01/2012.  Public Domain.