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Biomedical subjects

Kai M A Chan

Publications and source records attributed to Kai M A Chan.

8 recordsLinked to original sources
PubMed2006

Conservation planning for ecosystem services.

Despite increasing attention to the human dimension of conservation projects, a rigorous, systematic methodology for planning for ecosystem services has not been developed. This is in part because flows of ecosystem services remain poorly characterized at local-to-regional scales, and their protection has not generally been made a priority. We used a spatially explicit conservation planning framework to explore the trade-offs and opportunities for aligning conservation goals for biodiversity with six ecosystem services (carbon storage, flood control, forage production, outdoor recreation, crop pollination, and water provision) in the Central Coast ecoregion of California, United States. We found weak positive and some weak negative associations between the priority areas for biodiversity conservation and the flows of the six ecosystem services across the ecoregion. Excluding the two agriculture-focused services-crop pollination and forage production-eliminates all negative correlations. We compared the degree to which four contrasting conservation network designs protect biodiversity and the flow of the six services. We found that biodiversity conservation protects substantial collateral flows of services. Targeting ecosystem services directly can meet the multiple ecosystem services and biodiversity goals more efficiently but cannot substitute for targeted biodiversity protection (biodiversity losses of 44% relative to targeting biodiversity alone). Strategically targeting only biodiversity plus the four positively associated services offers much promise (relative biodiversity losses of 7%). Here we present an initial analytical framework for integrating biodiversity and ecosystem services in conservation planning and illustrate its application. We found that although there are important potential trade-offs between conservation for biodiversity and for ecosystem services, a systematic planning framework offers scope for identifying valuable synergies.

Biodiversity↗
PubMed2005

Leaky prezygotic isolation and porous genomes: rapid introgression of maternally inherited DNA.

Accurate phylogenies are crucial for understanding evolutionary processes, especially species diversification. It is commonly assumed that "good" species are sufficiently isolated genetically that gene genealogies represent accurate phylogenies. However, it is increasingly clear that good species may continue to exchange genetic material through hybridization (introgression). Many studies of closely related species reveal introgression of some genes without others, often with more rapid introgression of maternally inherited chloroplast or mitochondrial DNA (cpDNA, mtDNA). We seek a general explanation for this biased introgression using simple models of common reproductive isolating barriers (RIBs). We compare empirically informed models of prezygotic isolation (for pre- and postinsemination mechanisms of both female choice and male competition) with postzygotic isolation and demonstrate that rate of introgression depends critically upon type of RIB and mode of genetic inheritance (maternal versus biparental versus paternal). Our frequency-dependent prezygotic RIBs allow much more rapid introgression of biparentally and maternally inherited genes than do commonly modeled postzygotic RIBs (especially maternally inherited DNA). After considering the specific predictions in the context of empirical observations, we conclude that our model of prezygotie RIBs is a general explanation for biased introgression of maternally inherited genomic components. These findings suggest that we should use extreme caution when interpreting single gene genealogies as species phylogenies, especially for cpDNA and mtDNA.

Animals↗
PubMed2004

SYMMETREE: whole-tree analysis of differential diversification rates.

UNLABELLED: SymmeTREE implements several tests of differential diversification rates that exploit information on the topological distribution of species diversity throughout entire trees to address two general questions: (1) Has a given tree experienced significant variation in diversification rates among its branches? and (2) If so, along which branches have significant shifts in diversification rate occurred? These explicitly model-based methods are robust to uncertainty in estimates of branch length/duration and can accommodate incompletely resolved trees and other forms of phylogenetic uncertainty. AVAILABILITY: http://www.phylodiversity.net/bmoore/software.html CONTACT: brian.moore@yale.edu.

Algorithms↗
PubMed2004

The Golden Rule and the potentiality principle: future persons and contingent interests.

Duties to future persons are central to numerous key ethical issues including contraception, abortion, genetic selection, treatment of the environment, and population control. Nevertheless, we still seem to be lacking Parfit's 'Theory X', a general theory of beneficence whose appropriateness extends to future generations. Starting from the Golden Rule (TGR), R.M. Hare purportedly derived counterintuitive duties to potential people and 'the potentiality principle'. However, I argue that Hare's derivation involves a hidden and unjustifiable extension from TGR, and show how the most plausible form of TGR is compatible with multiple contradictory principles for the treatment of future persons. I appeal to our own preferences to argue that one extension of TGR follows the spirit of TGR, while the other is deeply implausible. Using the plausible extension, I derive a Contingent Interests Principle (CIP) that offers much promise as Parfit's elusive Theory X. In contrast to Hare's interpretation of TGR, this application provides solid justification for rejecting the potentiality principle.

Abortion, Induced↗
PubMed2002

Whole-tree methods for detecting differential diversification rates.

Prolific cladogenesis, adaptive radiation, species selection, key innovations, and mass extinctions are a few examples of biological phenomena that lead to differential diversification among lineages. Central to the study of differential diversification rates is the ability to distinguish chance variation from that which requires deterministic explanation. To detect diversification rate variation among lineages, we propose a number of methods that incorporate information on the topological distribution of species diversity from all internal nodes of a phylogenetic tree. These whole-tree methods (M(Pi), M(Sigma), and M(R)) are explicitly connected to a null model of random diversification--the equal-rates Markov (ERM) random branching model--and an alternative model of differential diversification: M(Pi) is based on the product of individual nodal ERM probabilities; M(Sigma) is based on the sum of individual nodal ERM probabilities, and M(R) is based on a transformation of ERM probabilities that corresponds to a formalized system that orders trees by their relative symmetry. These methods have been implemented in a freely available computer program, SYMMETREE, to detect clades with variable diversification rates, thereby allowing the study of biological processes correlated with and possibly causal to shifts in diversification rate. Application of these methods to several published phylogenies demonstrates their ability to contend with relatively large, incompletely resolved trees. These topology-based methods do not require estimates of relative branch lengths, which should facilitate the analysis of phylogenies, such as supertrees, for which such data are unreliable or unavailable.

Animals↗