Intellectual Merit:

Why does biological diversity tend to increase towards the tropics and decrease towards the poles? The reasons for this pattern have been debated and likely involve a combination of environmental conditions but also the degree of competition among species over shared resources. We set out to answer this question with a unique dataset from the National Ecological Observatory Network (NEON), consisting of small mammals across the United States and measures of their body sizes.  We found that although temperature explained some of the variation in diversity at the continental scale, it was the degree of competition that explained the most variation in diversity, represented by the degree to which species overlapped each other in body sizes. Our findings imply that increased mammal diversity is enabled by species-specific specialization on resources to avoid competition, which tends to be more intense in warmer regions. This insight would not have been possible without explicitly accounting for individual body sizes and leveraging a continent-wide observational network; most classic work on species coexistence used only species mean body size values within a single ecosystem.

We also applied this framework to understand the patterns of bird biodiversity across the globe, and implications for climate change. Ecologists have long thought that species in the tropics, where climate and food supply are more stable, may be more sensitive to environmental change if they have less variability among their individual members. Yet support for this idea at a global scale was lacking. We tested this idea by comparing body sizes of birds in the tropics with their close relatives in cooler, and less stable conditions in temperate regions. We found that indeed, tropical species had less variable body sizes than their temperate relatives and are thus more likely to be sensitive to environmental change. This study highlights the use of intraspecific variation in understanding where species are most sensitive to environmental change, including climate change.

Broader Impacts: In all, six peer-reviewed publications resulted from this award, and involved undergraduate, graduate, and postdoc authors in addition to the PIs. We placed a high priority on open science, including open access publications, and data and code for analyses deposited in public repositories. Undergraduates, graduate students, and postdoctoral associates were involved in this research through data collection, analysis, interpretation, manuscript writing, and presentation of results through peer-reviewed manuscripts and oral and poster presentations at local to international conferences. In addition to undergraduate research assistants during fall and spring semesters, four Research Experience for Undergraduate (REU) students participated in the research, and received training in. We placed a high priority on increasing opportunities for under-represented students in STEM including: women, the first to attend college and graduate school in their family, African American, Mexican American, and Asian students. A key component of this work involved the creation and teaching of undergraduate teaching modules on the ecological concepts of ?Size, Niches, and the Latitudinal Diversity Gradient?, which are accessible to instructors through a peer-reviewed and open access publication.

We reached scientific audiences through numerous talks at universities and local to international scientific conferences, and through an organized session at the Ecological Society of America, ?Challenges and opportunities for investigating ecological communities across space and time: insights from coordinated research networks.? We engaged the public through a public symposium focused on ?Citizen Science in a Changing World? during the 2018 annual Michigan State University Science Festival which attracts over 20,000 public attendees in a week-long celebration of science for all ages. This Science Pub event included short presentations and a panel discussion on local and global citizen science efforts to conserve biodiversity.

Last Modified: 04/26/2019
Modified by: Benjamin H Baiser