Papers by Margaret "Maggie" J Sporck-Koehler
AimThe taxon cycle hypothesis describes the cyclic movement of taxa during range expansion and co... more AimThe taxon cycle hypothesis describes the cyclic movement of taxa during range expansion and contraction, accompanied by an evolutionary shift from open and often coastal vegetation to closed, and often inland forest vegetation in island systems. The Hawaiian Archipelago is an ideal system to test this hypothesis given the linear fashion of island formation and a relatively well-understood geological history.LocationHawaiian Islands.MethodsWe sampled 153 individuals in 15 of the 16 native species of HawaiianEuphorbiasectionAnisophyllumon six major Hawaiian Islands, plus 11 New World close relatives, to elucidate the biogeographic movement of this lineage along the Hawaiian island chain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference for phylogenetic reconstruction. Connectivity among islands and habitat types was estimated using BayesTraits. Age and phylogeographic patterns were c...
PhytoKeys, 2016
Two species of Coprosma (Rubiaceae) J.R.Forst. & G.Forst. are described from the island of Maui o... more Two species of Coprosma (Rubiaceae) J.R.Forst. & G.Forst. are described from the island of Maui of the Hawaiian Archipelago. A newly described taxon, Coprosma cordicarpa J.Cantley, Sporck-Koehler, & M.Chau, sp. nov. is locally common in medium to high elevation dry forests and shrublands of leeward East Maui. The second taxon is resurrected from the synonymy of C. foliosa A.Gray as C. stephanocarpa Hillebr. and occurs in mesic to wet rainforests of both East and West Maui. Both taxa are segregated from C. foliosa, with which they share similar morphological characters. A conspicuous and persistent calyx of the fruit and various floral characters most easily differentiate both taxa from other Hawaiian taxa. The newly described Coprosma cordicarpa is further distinguished from C. stephanocarpa by a central constriction of the fruit with a depressed apex, which gives it a characteristic heart shape. Furthermore, the taxa are largely separated phenologically, ecologically, and geographically. Descriptions, conservation status, and specimens examined for the new species are included.
Journal of Experimental Botany, 2020
Since C4 photosynthesis was first discovered >50 years ago, researchers have sought to underst... more Since C4 photosynthesis was first discovered >50 years ago, researchers have sought to understand how this complex trait evolved from the ancestral C3 photosynthetic machinery on >60 occasions. Despite its repeated emergence across the plant kingdom, C4 photosynthesis is notably rare in trees, with true C4 trees only existing in Euphorbia. Here we consider aspects of the C4 trait that could limit but not preclude the evolution of a C4 tree, including reduced quantum yield, increased energetic demand, reduced adaptive plasticity, evolutionary constraints, and a new theory that the passive symplastic phloem loading mechanism observed in trees, combined with difficulties in maintaining sugar and water transport over a long pathlength, could make C4 photosynthesis largely incompatible with the tree lifeform. We conclude that the transition to a tree habit within C4 lineages as well as the emergence of C4 photosynthesis within pre-existing trees would both face a series of challeng...
Two species of Coprosma (Rubiaceae) J.R.Forst. & G.Forst. are described from the island of Maui o... more Two species of Coprosma (Rubiaceae) J.R.Forst. & G.Forst. are described from the island of Maui of the Hawaiian Archipelago. A newly described taxon, Coprosma cordicarpa J.Cantley, Sporck-Koehler, & M.Chau, sp. nov. is locally common in medium to high elevation dry forests and shrublands of leeward East Maui. The second taxon is resurrected from the synonymy of C. foliosa A.Gray as C. stephanocarpa Hillebr. and occurs in mesic to wet rainforests of both East and West Maui. Both taxa are segregated from C. foliosa, with which they share similar morphological characters. A conspicuous and persistent calyx of the fruit and various floral characters most easily differentiate both taxa from other Hawaiian taxa. The newly described Coprosma cordicarpa is further distinguished from C. stephanocarpa by a central constriction of the fruit with a depressed apex, which gives it a characteristic heart shape. Furthermore, the taxa are largely separated phenologically, ecologically, and geographically. Descriptions, conservation status, and specimens examined for the new species are included.
Cyanea konahuanuiensis Sporck-Koehler, M. Waite, A.M. Williams, sp. nov., a recently documented, ... more Cyanea konahuanuiensis Sporck-Koehler, M. Waite, A.M. Williams, sp. nov., a recently documented, narrowly endemic species from the Hawaiian Island of O‘ahu, is described and illustrated with photographs from the field. The closest likely relatives to the species, current conservation needs, and management future are discussed. It is currently known from 20 mature plants from two subpopulations and is restricted to a drainage below the Kōnāhua-nui summit (K1), the highest summit of the Ko‘olau Mountains, located on Windward O‘ahu. It differs from all other Cyanea species by its combination of densely pubescent leaves, petioles, and flowers; sparsely pubescent to glabrous stems, long calyx lobes, and staminal column being adnate to the corolla.
International Journal of Plant Sciences, Jan 12, 2009
Linkages among leaf traits and environment have most often been tested across communities but inf... more Linkages among leaf traits and environment have most often been tested across communities but infrequently within lineages. We studied seven endemic Hawaiian Plantago taxa radiated across elevations, climates, and habitats. We grew plants of six taxa in controlled conditions for 1–2 yr and collected leaves from a seventh in the field. For all taxa, we measured 46 leaf traits and tested hypotheses for trait-environment and trait-trait associations. Because of the rarity of the study plants, our study included low replication within taxa and multiple growth locations; despite these limitations, given reasonable assumptions, our analyses pointed to genetic differentiation among taxa. The leaves of bog taxa were smaller and thicker than those of woodland taxa, with higher leaf mass per area (LMA), stomatal pore area per leaf area, and carbon isotope discrimination d13C). Taxa from higher elevations had thicker leaves and higher LMA, as well as lower nitrogen per mass and higher adaxial stomatal distribution. Taxa of drier sites had higher vein density andd13C. Many traits were allometrically related to leaf area, including stomatal density, major vein densities, and xylem conduit numbers and dimensions. Stomatal and xylem traits were correlated, indicating a matching of hydraulic supply and demand. Leaf diversification in Hawaiian Plantago involved coordinated trait shifts, generating strong, apparently adaptive trait linkages.
Book Chapter by Margaret "Maggie" J Sporck-Koehler
Biomes and Ecosystems: An Encyclopedia
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Papers by Margaret "Maggie" J Sporck-Koehler
Book Chapter by Margaret "Maggie" J Sporck-Koehler