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Sensitivity analysis, the study of how ecological variables of interest respond to changes in external conditions, is a theoretically well-developed and widely applied approach in population ecology. Though the application of sensitivity analysis to predicting the response of species-rich communities to disturbances also has a long history, derivation of a mathematical framework for understanding the factors leading to robust coexistence has only been a recent undertaking. Here we suggest that this development opens up a new perspective, providing advances ranging from the applied to the theoretical. First, it yields a framework to be applied in specific cases for assessing the extinction risk of community modules in the face of environmental change. Second, it can be used to determine trait combinations allowing for coexistence that is robust to environmental variation, and limits to diversity in the presence of environmental variation, for specific community types. Third, it offers general insights into the nature of communities that are robust to environmental variation. We apply recent community-level extensions of mathematical sensitivity analysis to example models for illustration. We discuss the advantages and limitations of the method, and some of the empirical questions the theoretical framework could help answer.

SummaryAutophagy is a lysosome-mediated self-degradation process of eukaryotic cells that, depending on the cellular milieu, can either promote survival or act as an alternative mechanism of programmed cell death (PCD) in terminally differentiated cells. Despite the important developmental and medical implications of autophagy and the main form of PCD, apoptosis, orchestration of their regulation remains poorly understood. Here, we show in the nematode Caenorhabditis elegans, that various genetic and pharmacological interventions causing embryonic lethality trigger a massive cell death response that has both autophagic and apoptotic features. The two degradation processes are also redundantly required for normal development and viability in this organism. Furthermore, the CES-2-like basic region leucine-zipper (bZip) transcription factor ATF-2, an upstream modulator of the core apoptotic cell death pathway, is able to directly regulate the expression of at least two key autophagy-related genes, bec-1/ATG6 and lgg-1/ATG8. Thus, the two cell death mechanisms share a common method of transcriptional regulation. Together, these results imply that under certain physiological and pathological conditions, autophagy and apoptosis are co-regulated to ensure the proper morphogenesis and survival of the developing organism. The identification of apoptosis and autophagy as compensatory cellular pathways in C. elegans might help us to understand how dysregulated PCD in humans can lead to diverse pathologies, including cancer, neurodegeneration and diabetes.

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Darwin’s mechanistic explanation for the emergence and maintenance of biological diversity provides the conceptual basis for a self-consistent theory of ecology that relies on a coherent system of seven Darwinian principles. A universal population dynamic concept of fitness connects the principles through robust mathematical relations, enabling the formal treatment of alleles (selfish genes) and the individuals of clones or sexual species within the same logic. The central thesis of the theory is that the inevitable checks on the inherent capacity of life for exponential growth lead either to regulated, robust coexistence or to competitive exclusion among different variants. As fitness is constrained by inescapable trade-offs between its components, the ultimate competitive victory of a perfect organism (‘Darwinian demon’) is impossible and coexistence may follow. Besides basic concepts like dynamical system, state description, fitness, regulation, impact, and sensitivity, the crucial method of timescale separation is also explained and illustrated.

Taking a fresh look at Darwin’s original theory of the origin of species and following the road paved by Gause, Hutchinson, MacArthur, and Levins a consistent system of fundamental principles is revealed, one that makes the integration of ecology possible. These principles are explained, formalized, and illustrated by mutually compatible mathematical models in this book, demonstrating how this coherent modelling approach helps to explain or predict actual population and community dynamics and patterns on the field or in the lab. At the core of the Darwinian theory of ecology lies a generalized fitness concept applicable to populations of alleles and clones as well as of conspecific individuals. It is the theory of structured populations that provides a universal methodology to calculate the fitness of any reproductive unit in the face of any complexity arising from differences in individual states. The inherent capacity of all living organisms to increase their populations exponentially is necessarily constrained by resource depletion or natural enemies, so that the ultimate growth rate of persistent populations is regulated. Competition between different reproductive units leads either to competitive exclusion or to robust coexistence, depending on how similarly they are regulated. This is shown in general and demonstrated with several types of model. A generalized and formalized niche theory consistent with the principles is explicated, discussed, and illustrated by empirical studies. Studies on global, regional, and local ecological patterns close the book, discussed in the spirit of the process-based approach of Darwinian ecology.