Final answer:
A pseudoxylaria infestation in a termite mound would negatively affect geckos in the ecosystem due to competition for resources.
Step-by-step explanation:
A widespread pseudoxylaria infestation in a termite mound would negatively affect a population of geckos in the ecosystem through competition for resources. Pseudoxylaria competes with termitomyces, a fungus that provides food for termites. With the infestation, the termites may not have enough food to support a healthy population, which would in turn reduce the food available for geckos, leading to a decline in their population.