For publications earlier than 2019, view our publications archive.
2011 |
Karlin, Eric F.; Hotchkiss, Sara C.; Boles, Sandra B.; Stenøien, Hans K.; Hassel, Kristian; Flatberg, Kjell I.; Shaw, A. Jonathan: High genetic diversity in a remote island population system: sans sex. In: New Phytologist, vol. 193, iss. 4, pp. 1088-1097, 2011. (Type: Journal Article | Abstract | Links)@article{Karlin2011,It has been proposed that long-distance dispersal of mosses to the Hawaiian Islands rarely occurs and that the Hawaiian population of the allopolyploid peat moss Sphagnum palustre probably resulted from a single dispersal event. • Here, we used microsatellites to investigate whether the Hawaiian population of the dioicous S. palustre had a single founder and to compare its genetic diversity to that found in populations of S. palustre in other regions. • The genetic diversity of the Hawaiian population is comparable to that of larger population systems. Several lines of evidence, including a lack of sporophytes and an apparently restricted natural distribution, suggest that sexual reproduction is absent in the Hawaiian plants. In addition, all samples of Hawaiian S. palustre share a genetic trait rare in other populations. Time to most recent ancestor (TMRCA) analysis indicates that the Hawaiian population was probably founded 49–51 kyr ago. • It appears that all Hawaiian plants of S. palustre descend from a single founder via vegetative propagation. The long-term viability of this clonal population coupled with the development of significant genetic diversity suggests that vegetative propagation in a moss does not necessarily preclude evolutionary success in the long term. |
Kellner, James R.; Asner, Gregory P.; Vitousek, Peter M.; Tweiten, Michael A.; Hotchkiss, Sara; Chadwick, Oliver A.: Dependence of Forest Structure and Dynamics on Substrate Age and Ecosystem Development. 2011. (Type: Bachelor Thesis | Abstract | Links)@bachelorthesis{Kellner2011,We quantified rates, sizes, and spatial properties of prevailing disturbance regimes in five tropical rain forest landscapes on a substrate-age gradient in Hawaii. By integrating measurements from airborne LiDAR with field studies and statistical modeling, we show that the structure and dynamics of these forests respond to processes that change during the development of ecosystems. On young substrates of 0.3 ky where forests are in primary succession and are limited by N, mean canopy height was 13 m and height decreases more than 1 m occurred in small, isolated events (power-law exponent = 1.69 ± 0.02, n = 61 gaps ha−1). The proportion of the landscape affected by disturbance increased on high-fertility intermediate-aged substrates of 5–65 ky and canopies were heterogeneous. Frequencies of height decreases more than 1 m were n = 14, 18, and 30 gaps ha−1 corresponding to power-law exponents of 2.188 ± 0.02, 2.220 ± 0.03, and 1.982 ± 0.02 on substrates of 5, 20, and 65 ky. There was a substantial difference between forests on a 150 ky substrate and sites of 5–65 ky; trees on the older substrate formed patchworks of stunted cloud-forest and stands of taller-stature trees. The frequency of recent disturbance events more than 1 m was n = 48 gaps ha−1, corresponding to a power-law exponent of 1.638 ± 0.01. Across the substrate-age gradient, the proportion of each landscape that decreased in height by more than 1 m was 0.16, 0.40, 0.41, 0.36, and 0.17, respectively. These findings demonstrate that substrate age and processes associated with ecosystem development can mediate the rates, sizes, and spatial characteristics of disturbance regimes on forested landscapes, and point toward the necessity of large-area samples to obtain robust estimates of natural dynamics. |
2009 |
Alexander, M. L.; Hotchkiss, S. C.: Bosmina remains in lake sediment as indicators of zooplankton community composition. In: Journal of Paleolimnology, vol. 43, pp. 51-59, 2009. (Type: Journal Article | Abstract | Links)@article{Alexander2009,We measured Bosmina spp. mucro and antennule lengths in surface sediment samples from Wisconsin lakes to test whether such measures could be used to reconstruct zooplankton community composition and size structure in paleolimnological studies. Our data set included 58 lakes of various depths, water chemistry, trophic state, macrophyte cover, and zooplankton community composition. We used non-metric multidimensional scaling ordination (NMS) and simple correlation analysis to assess whether mucro and antennule measurements reflect the zooplankton community size structure. Bosmina mucro length (r = 0.727, p < 0.05) and antennule length (r = 0.360, p < 0.05) correlated with the NMS axis, which essentially represents zooplankton community size structure. Bosmina mucro length correlated positively with the abundance of the large-bodied zooplankter Epischura lacustris (r = 0.364, p < 0.01), as well as Diacyclops thomasi (r = 0.256, p < 0.05), and Leptodiaptomus minutus (r = 0.578, p ≤ 0.001), but correlated negatively with the abundance of the small-bodied zooplankter Tropocyclops prasinus (r = −0.385, p < 0.01). Bosmina antennule length correlated positively with the abundance of L. minutus (r = 0.344, p < 0.01) and negatively with T. prasinus (r = −0.258, p < 0.05). This broad, spatial scale assessment supports the use of Bosmina mucro and antennule lengths as a proxy for zooplankton community size structure. Mucro length is a stronger indicator of zooplankton community size structure as seen in its strong correlation with the NMS axis 1 and the significant correlations with abundance of predatory copepods. |