What do human economies, large islands and forest fragments reveal about the factors limiting ecosystem evolution?

What factors limit ecosystem evolution? Like human economies, ecosystems are arenas where agents compete for locally limiting resources. Like economies, but unlike genes, ecosystems are not units of selection. In both economies and ecosystems, productivity, diversity of occupations or species and intensity of competition presuppose interdependence among many different agents. In both, competitive dominants need abundant, varied resources, and many agents' products or services, to support the activity and responsiveness needed to maintain dominance. Comparing different-sized land masses suggests that productivity is lower on islands whose area is too small to maintain some of the interdependences that maintain diversity, productivity and competitiveness in mainland ecosystems. Islands lacking the rare, metabolically active dominants that make competition so intense in mainland ecosystems are more easily invaded by introduced exotics. Studies of islets in reservoirs identify mechanisms generating these phenomena. These phenomena suggest how continued fragmentation will affect future 'natural' ecosystems.

Molecular phylogenetics and the evolution of labral spines among eastern Pacific ocenebrine gastropods.

Labral spines are sharp projections of the apertural lip found in some marine gastropods that are used to penetrate hard-shelled prey. The majority of gastropod genera that contain labral spine-bearing species are found in the subfamily Ocenebrinae (Gastropoda: Muricidae). To reconstruct the evolutionary history of labral spine-bearing and labral spine-lacking gastropods in the eastern Pacific (EP) Ocean, partial sequences of two mitochondrial genes (cytochrome oxidase I and 12S rRNA) were obtained from representative taxa. Despite high nucleotide bias, a variety of phylogenetic reconstruction methods produced the same tree topology. The traditional taxonomic view that all "Nucella-like" spine-bearing taxa in the EP belong to a monophyletic "Acanthina" is rejected due to nonmonophyly of this group. The more recently recognized "Acanthinucella" is also not monophyletic, and we therefore propose the new genus Mexacanthina for two Mexican species formerly assigned to Acanthinucella. The genus Ocinebrina, which first appears in the middle Eocene, is not a stem EP ocenebrine lineage and may also not be a monophyletic clade. Tracing the evolutionary history of labral spines among extant lineages indicates that the absence of a labral spine is ancestral for all EP ocenebrines. Ancestral conditions could not be resolved unambiguously for all nodes of the phylogeny based on extant taxa. However, by jointly considering both molecular phylogenetic relationships and the phylogenetic affinities of several extinct taxa, all remaining character state transformation can be inferred unambiguously. Based on this analysis, a labral spine likely evolved independently in at least four lineages of EP ocenebrines. Although homoplasy appears to characterize labral spine evolution among ocenebrine gastropods, the structural position of a labral spine was evolutionarily altered in one lineage, indicating that different types of labral spines do not necessarily reflect convergent evolution.

When biotas meet: understanding biotic interchange.

When the barrier between biotas with long separate histories breaks down, species invade from one biota to the other. Studies of episodes of marine and terrestrial biotic interchange that have occurred during the last 20 million years show that large-scale extinction of species before the onset of interchange renders biotas especially prone to invasion. As environments and species are being exploited and eliminated on an ever increasing scale in the human-dominated biosphere, the geographical expansion of species from biotas in which evolution of high competitive, defensive, and reproductive abilities has proceeded the furthest will become more frequent. Historical events and interactions are essential ingredients for understanding the current and future structure and composition of the world's biota.

The First Historical Extinction of a Marine Invertebrate in an Ocean Basin: The Demise of the Eelgrass Limpet Lottia alveus.

Lottia alveus, a gastropod limpet once found only on the blades of the eelgrass Zostera marina from Labrador to New York in the western Atlantic Ocean, is the first marine invertebrate known to have become extinct in an ocean basin in historical time. The last known specimens were collected in 1929, immediately prior to the catastrophic decline of Zostera in the early 1930s in the North Atlantic Ocean. The brackish water refugium of Zostera throughout the decline was apparently outside of this gastropod's physiological range, and the limpet became extinct. Few marine invertebrates have habits as specialized and ranges and tolerances as narrow as did L. alveus. The fact that most marine invertebrates have large effective population sizes may account for their relative invulnerability to extinction.

Predation through geological time: evidence from gastropod shell repair.

Warm-water marine gastropods from soft-bottom habitats show an increase in the incidence of breakage-resistant shell characteristics over geological time. The hypothesis that breakage became a more important component of selection in the middle of the Mesozoic Era is supported by the finding that frequencies of breakage-induced shell repair increased from the Pennsylvanian and Triassic periods to the Cretaceous, Miocene, and Recent.

Biological versatility and earth history.

Examples from various plant and animal groups indicate that there has been a general increase in potential versatility of form, determined by the number and range of independently varying morphogenetic parameters, among taxa appearing at successively younger stages in the fossil record. Taxa or body plans with higher potential versatility have tended to replace less potentially versatile groups in the same or similar adaptive zone through time. Greater potential diversity allows for greater homeostasis, efficiency, and integration of structures and functions, and for an increase in size of the potential adaptive zone. In contrast, chemical versatility has generally decreased within groups from the pre-Cambrian to the Phanerozoic, partly as the result of apparent changes in the chemical environment and partly as the consequence of selection for efficiency and greater metabolic ease of handling of certain materials.