2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ Oikos 112: 185 Á/195.The species Á/time relationship (STR) describes how the species richness of a community increases with the time span over which the community is observed. This pattern has numerous implications for both theory and conservation in much the same way as the species Á/area relationship (SAR). However, the STR has received much less attention and to date only a handful of papers have been published on the pattern. Here we gather together 984 community time-series, representing 15 study areas and nine taxonomic groups, and evaluate their STRs in order to assess the generality of the STR, its consistency across ecosystems and taxonomic groups, its functional form, and its relationship to local species richness. In general, STRs were surprisingly similar across major taxonomic groups and ecosystem types. STRs tended to be well fit by both power and logarithmic functions, and power function exponents typically ranged between 0.2 and 0.4. Communities with high richness tended to have lower STR exponents, suggesting that factors increasing richness may simultaneously decrease turnover in ecological systems. Our results suggest that the STR is as fundamental an ecological pattern as the SAR, and raise questions about the general processes underlying this pattern. They also highlight the dynamic nature of most species assemblages, and the need to incorporate time scale in both basic and applied research on species richness patterns.

Summary Hypoxic injury is a key pathological event in a variety of diseases. Despite the clinical importance of hypoxia, modulation of hypoxic injury mechanisms for therapeutic benefit has not been achieved suggesting that critical features of hypoxic injury have not been identified or fully understood. As mitochondria are the main respiratory organelles of the cell they have been the focus of much research into hypoxic injury. Previous research has focused on mitochondria as effectors of hypoxic injury, primarily in the context of apoptosis activation [1] and calcium regulation [2]; however, little is known about how mitochondria themselves are injured by hypoxia. Maintenance of protein folding is essential for normal mitochondrial function [3], while failure to maintain protein homeostasis (proteostasis) appears to be a component of ageing [4, 5] and a variety of diseases [6, 7]. Previously it has been demonstrated that mitochondria possess their own unfolded protein response [8–10] that is activated in response to mitochondrial protein folding stress, a response that is best understood in C. elegans. As hypoxia has been shown to disrupt ATP production and translation of nuclear encoded proteins [11], both shown to disrupt mitochondrial proteostasis in other contexts [3, 12], we hypothesized that failure to maintain mitochondrial proteostasis may play a role in hypoxic injury. Utilizing C. elegans models of global [13, 14], focal [15], and cell non-autonomous hypoxic injury we have found evidence of mitochondrial protein misfolding post-hypoxia, and that manipulation of the mitochondrial protein folding environment is an effective hypoxia protective strategy.

Aggregation of cytosolic proteins is a pathological finding in disease states, including ageing and neurodegenerative diseases. We have previously reported that hypoxia induces protein misfolding in Caenorhabditis elegans mitochondria, and electron micrographs suggested protein aggregates. Here, we seek to determine whether mitochondrial proteins actually aggregate after hypoxia and other cellular stresses. To enrich for mitochondrial proteins that might aggregate, we performed a proteomics analysis on purified C. elegans mitochondria to identify relatively insoluble proteins under normal conditions (110 proteins identified) or after sublethal hypoxia (65 proteins). A GFP-tagged mitochondrial protein (UCR-11 - a complex III electron transport chain protein) in the normally insoluble set was found to form widespread aggregates in mitochondria after hypoxia. Five other GFP-tagged mitochondrial proteins in the normally insoluble set similarly form hypoxia-induced aggregates. Two GFP-tagged mitochondrial proteins from the soluble set as well as a mitochondrial-targeted GFP did not form aggregates. Ageing also resulted in aggregates. The number of hypoxia-induced aggregates was regulated by the mitochondrial unfolded protein response (UPRmt) master transcriptional regulator ATFS-1, which has been shown to be hypoxia protective. An atfs-1(loss-of-function) mutant and RNAi construct reduced the number of aggregates while an atfs-1(gain-of-function) mutant increased aggregates. Our work demonstrates that mitochondrial protein aggregation occurs with hypoxic injury and ageing in C. elegans. The UPRmt regulates aggregation and may protect from hypoxia by promoting aggregation of misfolded proteins.