Final answer:
Diseases/viruses are a biotic limiting factor in an ecosystem, as they involve interactions among living organisms and can alter population sizes and community structures. An ecosystem ecologist or community ecologist would be ideal collaborators for assessing the impact of biotic factors such as E. coli in an environment.
Step-by-step explanation:
Diseases/viruses can be significant limiting factors in an ecosystem. Diseases are considered a type of biotic limiting factor because they involve interactions between living organisms. Diseases affect population dynamics and can alter community structures by reducing the population of affected species, potentially leading to increased space and resources for other species.
When considering the collaboration to better understand the impact of E. coli on beach visitors, an infectious disease specialist should collaborate with an ecosystem ecologist or a community ecologist, given that they study the interactions within communities including the diseases affecting those communities. Bacteria that can use atmospheric nitrogen are considered a biotic factor, as they are living organisms influencing ecosystems through processes like nitrogen fixation which directly impacts the nutrient cycles.