El Nino Effects on the Dynamics and Control of An Island Ecosystem in the Gulf of California

Abstract

The tremendous increase in precipitation associated with the 1992-1993 El Niñ o profoundly affected terrestrial communities on arid islands in the Midriff region of the Gulf of California. In 1992, winter precipitation was 5.4 times the historical mean, and winter precipitation over the entire El Niñ o was the highest two-year amount ever recorded. Increased precipitation led to an explosion of annual plant growth on the previously barren (0-4% cover) islands: plant cover increased 10-160 times over what it had been. With the resumption of arid conditions in 1994, live plant cover returned to the low levels seen before the onset of El Niño.Insect abundance tracked this pulse in plant productivity and approximately doubled in 1992 and 1993 compared to 1991 levels. In 1994, the crash of annual plants caused insect densities to drop to the lowest levels recorded during the 5-yr study. El Niñ o also affected the composition of the insect assemblage. In the dry years 1990-1991, the assemblage was dominated by insects feeding on products originating in the ocean: detritivores/scavengers on shore drift of marine algae and carcasses, avian parasites, and detritivores of bird products. Herbivores were extremely rare. The heavy plant growth in 1992 stimulated large (40-190 times pre-El Niñ o levels) increases in herbivores.The great increases in land plant biomass and insect abundance are indicative of an important change in the dynamics of this system. Previously, most material flowing through the food webs of these islands originated directly or indirectly in the ocean. In contrast, during this El Niñ o, most material originated via productivity by terrestrial plants. Thus, wet El Niñ os represent an agent that switches the system from one dependent primarily on allochthonous input to a system driven to a greater extent by in situ productivity. The influence of this pulse of terrestrial productivity extends beyond the El Niñ o years: the persistence and slow release of plant and detrital biomass reserves may also greatly affect dynamics for years after the El Niñ o event has passed. We suggest that large-scale climatic events such as El Niñ o may be long-lasting determinants of community dynamics rather than occasional disturbance events.

Effect of resource subsidies on predator–prey population dynamics: a mathematical model

“…The use of secondary resources by species from adjacent habitats or ecosystems is widespread [46,50,52]. These allochthonous resources, or resource subsidies, can strongly affect the abundance and space use of consumers in recipient ecosystems, with cascading effects on in situ resources [28,30,38,50,53].…”

“…For predator-prey systems that are dynamically unstable, the indirect effects of a second resource are often different from those predicted by equilibrium dynamics [6,7,46]. Adaption of predator behaviours, such as consumption rate constants and relative time spent in searching in distinct patches, can hinder predators from achieving an ideal free distribution and may instead promote oscillation or even chaos [3].…”

Animal water balance drives top-down effects in a riparian forest—implications for terrestrial trophic cascades

“…The evolution of terrestrial life has been driven by the challenge of maintaining water balance with scarce freshwater resources, but effects of animal water limitation on terrestrial food webs have received little attention, in contrast to plant-mediated bottom-up effects [1,[2][3][4][5]. This is a significant gap in our understanding of ecological dynamics, because over 40% of the earth's land surface is classified as drylands [6] and precipitation limits diversity of plants and animals at all but the highest latitudes globally, even outside of drylands [7].…”

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

“…Ecosystems on islands tend to be strongly bottom-upregulated environments, with marked seasonal and inter-annual variations in resource availability. This variation can be driven by climatic patterns [5] and marine to terrestrial interfaces in resource exchange, including seabird-driven nutrient subsidy [6]. The impact of these inputs on population dynamics can differ among habitats according to resource quality and availability [7,8].…”