James A. Drake’s research while affiliated with The University of Tennessee Medical Center at Knoxville and other places

The quest to understand animate nature, its origins, current state and future course, its dynamical underpinnings and interface with the physical world, is surely the tacit aspiration of contemporary ecology. As a field of inquiry, academic ecology emerged in earnest from the descriptive realm of natural history in the late nineteenth century when observers of nature, pondering similarity and difference, sought cause. Adopting the classic approach to science, ecologists further described, but also dissected, modeled, conceptualized, and manipulated the parts of ecological systems. What emerged is the modern framework of ecology, built upon the struts of population dynamics and tempered by interactions between species, all within an environmental context. Yet with the Earth as a laboratory containing millions of extant and evolving species, the number and variety of plausible ecological studies is functionally inexhaustible. A quick glance through any ecological journal reveals surprising novelty and nuance at every turn. Hence, one is compelled to ask whether progress in ecology is best served by strict adherence to a reductionistic program and unending description, or whether this approach should be blended with more general and epiphenomenological complements. This question is apropos to all of science. Attempts at such a synthesis are well underway sparked by the realities of a complex and decidedly nonlinear nature. In this complex nature one þ one need not always equal two, and the simple logical operator if–then requires else. In ecology, if and then produces a highly contingent mapping of their own accord. Add else, and we have the fundamental reason for the diversity of nature and the nuance of its expression.What then are mechanisms, the holy grail of reductionist ecology, but manifestations of an emergent nature? Nature can be described by the action of mechanisms explicit in our logical operator. Yet understanding nature requires a deeper knowledge of how the action of the mechanism emerged. Here we present a solution to the recalcitrant problem of true or hard emergence, the existence of which has been debated, demonized, and exalted for centuries. We suggest that emergence is hidden within the attractor space of dissipative dynamical systems, or more precisely the interaction between multiple attractors. Our arguments while tentative, suggest that two independent systems can interact in the attractor space and produce a persistent attractor that are essentially offspring of the parents. Emergence in this case is absolute because no trajectories exist linking the child to either parent. You cannot get there from here. Our arguments are based on a long series of experimental studies that have explored the assembly or construction of ecological communities. We offer this notion of emergence as a general solution to all things emergent independent of any particular system

The competition-colonization trade-off has long been considered an important mechanism explaining species coexistence in spatially structured environments, yet data supporting it remain ambiguous. Most competition-colonization research examines plants and the dispersal-linked traits of their seeds. However, colonization is more than just dispersal because rapid population growth is also an important component of colonization. We tested for the presence of competition-colonization trade-offs with a commonly used artificial assemblage consisting of protozoan and rotifer species, where colonization was the ability of a species to establish populations in patches. By ranking species according to their colonization abilities and their pairwise competitive interactions, we show that these species exhibit competition-colonization trade-offs. These results reveal that the competition-colonization trade-off exists within nonplant assemblages and that even in a laboratory setting, species are constrained to be either good competitors or colonizers but not both.

This chapter examines various concepts in community ecology that are difficult to observe in natural systems and examines some laboratory studies that document the production of ecological structure in multi-species systems. Two aspects of ecology have been explored where laboratory studies are crucial for the understanding of ecological phenomena. The first aspect is parameter (and measurement) oriented—what must be measured and how it should be done to make observations in ecological studies. Secondly, the interactive nature of ecological phenomena and the inability to reduce these processes to their constituent components have been explored. These two discussions implicitly address the relationship between reductionism and holism. It has been argued that laboratory studies are not only valid investigative tools, but may also better capture the essential dynamics of ecological systems compared with field studies. Through exploring the use of microcosms, the dynamic reality of ecological systems has been illustrated, and the systems in which explicit tests of these realities are possible have been examined. The chapter contrasts the laboratory approach with the field and model approaches to identify the prescriptive role for laboratory microcosms in ecological research.

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A recent explanation of the declining species richness gradient with increasing latitude away from the tropics implicated broad scale habitat variability, an associated range expansion, and a resulting increase in niche breadth. The niche breadth in turn was thought to affect richness by competition and rescue effect. While all three factors appear to be correlated, neither the postulated nor alternative causal mechanisms have been tested. We conduct such a test using a system which has all the attributes of the large scale pattern but which, in contrast to continental scale observations, allows for estimation or control of crucial variables such as taxonomic composition, habitat heterogeneity, habitat variability, exact species distribution, and local richness. Specifically, we test the alternative that the correlation between the geographical range of species and local diversity is a function of differential species survival and link this phenomenon to habitat variability. We use 40 species of aquatic invertebrates inhabiting a landscape of 49 miniature rock pools on the coast of Jamaica. The system we examined exhibits a gradient of increasing richness with decreasing habitat variability, analogous to the broad scale latitudinal pattern. Furthermore, species with broader ecological ranges are also broadly distributed. Superficially, this appears to be in agreement with the older explanations but two facts suggest different causes. First, there is no evidence of a rescue effect maintaining high richness in many habitats despite their proximity to species sources. Second, ecologically broad species coexist with habitat specialists without reducing richness in jointly occupied habitats.

Relative variability of species has been shown to increase significantly with a decrease in their ecological range. Similarly, the distribution of collapse (e.g., extinctions, disturbances, population declines) magnitudes has also been shown to follow an inverse power-law form described by the 1/f(omega) curve. We hypothesized that the two, possibly general, patterns associated with ecological systems share a common underlying cause: the hierarchical structure of the system itself. To test the hypothesis we used a model system of 49 natural rock pools inhabited by 40 species of invertebrates. Three measures of species variability based on changes in abundance, distribution, and persistence in individual pools conform with the postulated negative exponential curves. Correspondingly, frequency distributions of changes of various magnitudes conform to the 1/f(omega) pattern. Examination of the contributions of species to the 1/f(omega) pattern revealed that species low in the system hierarchy (habitat specialists in this case) are responsible for the majority of small variation events (correlations between the ecological range and position on the 1/f(omega) curve range from 0.625 to 0.807 on the three measures of variability). This permits the conclusion that the two patterns are linked and constitute different expressions of the same hierarchical system structure.