COEXISTENCE, RESILIENCE AND RESISTANCE OF MARINE INVERTEBRATE COMMUNITIES ACROSS A LATITUDINAL GRADIENT

Abstract

Biogeographic barriers have limit the movement of organisms, leading to speciation and shaping the development of unique regional biotas. Human-aided circumvention of biogeographic barriers, however, has increased the connectivity of isolated biotas, while changes in climate have been altering species geographic ranges, restructuring ecological networks, modifying ecological niche arrangements and increasing the frequency and intensity of natural pulse disturbances. In this context, examination of some of the most fundamental processes underlying the patterns of species diversity and community structure across biogeographical scales is therefore vital, especially as humans increasingly modify these relationships established over the course of geological history. The latitudinal diversity gradient is the most well-established and predominantly studied biogeographic diversity pattern on Earth. Higher tropical biodiversity with a decline towards higher latitudes occur in both hemispheres and has been observed for various systems including terrestrial, freshwater and marine. In my dissertation, I explored latitudinal variation in factors that can inform and modify fundamental ecological principles such as coexistence, community stability, and resistance. I studied communities of marine invertebrates across over 7000 km of continuous coastal habitat spanning 47-degree latitudinal range on the Eastern North and Central Pacific coast, from tropical Panama to subarctic Alaska. Experiments were based on the manipulation of recently recruited or adult communities of sessile marine invertebrates, such as barnacles, marine worms and encrusting colonial organisms. These organisms inhabit coastal ecosystems across continental scales and can colonize artificial substrates such as hull of commercial vessels that travel across oceans serving as vectors for marine biological invasions. Among my three aims I was able to: (1) examine how the complementarity of ecological niches varies from the tropics to subarctic among recruiting taxa, and how the differentiation of these recruitment pulses through time help inform coexistence across large spatial scales; (2) document distinct resilience responses to pulse disturbances between lower and high latitude sites, while exploring the interplay between compositional and functional recovery in biological communities; and finally, (3) implement a novel component to pre-existing models to predict probability of biological invasions based on the distinct pressures of propagule introduction, environmental similarity between donor and recipient regions, and the potential for biotic resistance. My dissertation yields empirical evidence of processes varying with latitude, advancing our knowledge in some of the most fundamental questions in classic and contemporary ecology. Large-scale documentation of the mechanisms and processes that maintain global patterns of biodiversity are uppermost in the design of global conservation strategies, especially in a more connected world.