Dr. Susan J. MazerAssociate Professor of Ecology & Evolution
Department of Ecology, Evolution & Marine Biology
University of California
Santa Barbara, California 93106
Phone: 805-893-8011
FAX: 805-893-4724
e-mail: mazer@lifesci.ucsb.edu
Ongoing Project: Photographic Guide to Lowland Rainforest Fruits and Seeds from Madre de Dios (Peru)
Picture of me, on a Bad Hair
Day
Dr. Susan J. Mazer
Associate Professor of Ecology & Evolution
Department of Ecology, Evolution & Marine Biology
University of California
Santa Barbara, California 93106
Phone: 805-893-8011
FAX: 805-893-4724
e-mail: mazer@lifesci.ucsb.edu
EDUCATION:
1981; B.S. Biology; Yale University
1983; M.S. Botany; University of California, Davis
1986; Ph.D. Botany; University of California, Davis
1986 - 1988: Postdoctoral Research Fellowship, Department of Paleobotany,
National Museum of Natural History, Smithsonian Institution, Washington,
D.C.
FOREIGN LANGUAGE FLUENCY: Spanish, French
Research
Interests:
The theme of my research program is to examine evolutionary processes
occurring in wild plant taxa. I've been interested in the process and outcome
of evolution by natural selection at three ecological scales: populations,
communities, and higher taxa. In a variety of research projects,
I've pursued three main goals:
(1) To determine the evolutionary significance of phenotypic variation in quantitative life history parameters, gender expression, floral traits, and reproductive components in wild plant populations. I have focused on quantitative traits (as opposed to discrete characters) because they are widespread and include a wide range of fitness-related traits in natural populations. The study of phenotypic variation in quantitative traits requires the use quantitative genetic methods to detect the component of this variation that is "visible" to natural selection (i.e., the heritable component).
(2) To detect the mechanisms by which natural selection operates to cause - or may be prevented from effecting - evolutionary change in fitness-related traits in populations inhabiting heterogeneous environments. I have been interested in the search for "constraints" on the rate of evolutionary change, including the detection and estimation of: Genotype x Environment interactions, environment-specific heritabilities and genetic covariances, phenotypic plasticity of fitness-related traits, maternal environmental effects on progeny phenotype, and strong environmental (including ontogenetic) components of variation that may delay the rate of genetic change in quantitative traits.
(3) To examine the distribution of reproductive characters and ecological preferences among species, in order to detect patterns that appear to result from long-term ecological and evolutionary processes. In contrast to detailed demographic and genetic studies within species, studies of interspecific variation in life history and reproductive characters rely on the statistical analysis of broad-scale comparative surveys and phylogenetic patterns. Interspecific studies can be used to test the "null" hypotheses that life history and/or reproductive characters of wild species are independent of the kinds of habitats they occupy or of their ecological role. A variety of quantitative methods are now at hand (although hotly debated) to evaluate inter-specific data, but most involve conducting broad-scale comparative surveys that evaluate the joint distribution of reproductive characters and ecological attributes across a taxonomically diverse array of species or within monophyletic groups of which the phylogeny is well-established.
My current research projects include the following.
I. The Efficacy of Natural Selection in Wild Plant Species
Project 1: Quantitative genetic variation and covariation among floral traits in the sand-spurrey, Spergularia marina (Caryophyllaceae): a test of some central assumptions of sex allocation theory.
Since 1991, Dr. Veronique Delesalle (Department of Biology, Gettysburg College, Pennsylvania) and I have been examining empirically several assumptions intrinsic to theoretical models of the evolution of sex allocation and sexual specialization in hermaphroditic organisms. The two most common assumptions are that:
Only within the last few years have evolutionary geneticists begun to examine whether these assumptions apply to plants. The delay in evaluating these assumptions empirically in plants has been partly due to the difficulties associated with measuring sexual expression and partly due to the fact that many species show limited variation in the allocation of resources to male or to female function.
Using a combination of approaches - sampling wild populations, artificial selection experiments, the cultivation of distinct genetic lineages in a controlled environment, and the experimental manipulation of abiotic environmental conditions - we are investigating environmental and genetic sources of variation in gender expression and other floral traits in Spergularia marina. This annual species is particularly suitable for our work because it exhibits remarkably high levels of phenotypic variation in gender expression. (Investment in male function varies from 0 to 10 stamens per flower, while investment in female reproduction varies from 40 - 180 ovules per flower and from ~30 - 100 seeds per fruit).
We have discovered that wild populations differ in the magnitude of ontogenetic variation, in the degree of maternally-transmitted variation in primary and secondary sexual traits, and in their genetic architecture (the pattern of genetic correlations among traits). These results suggest that populations are evolving along different evolutionary trajectories and may be subject to different evolutionary "constraints". In addition, in a study of correlations among maternal family means in four wild populations, and following one generation of strong artificial selection, we detected no evidence to support the widespread assumption or belief that there is an inherent genetic trade-off between male and female investment per flower. Rather, trade-offs between male and female function are likely to be detected only at the level of the entire individual or genotype.
In considering our results, we developed a tentative hypothesis to explain the absence of a negative genetic correlation between pollen production and ovule production at the level of individual flowers (Mazer and Delesalle, Evolutionary Ecology, in press). Briefly, in highly autogamous (self-fertilizing) species such as Spergularia marina, two factors should favor the evolution of an "optimal" pollen:ovule ratio expressed by individual flowers: first, the inability of genotypes to exhibit gender specialization and, second, the presence of strong stabilizing selection favoring genotypes with an efficient pollen:ovule ratio. In spite of strong stabilizing selection on the pollen:ovule ratio, populations may be expected to maintain genetic variation in ovule and pollen production per flower even among genotypes that exhibit similar pollen:ovule ratios. That is, genotypes with high levels of ovule and pollen production per flower (but with relatively low lifetime flower and fruit production) should be able to coexist with genotypes producing relatively few ovules and pollen per flower (but with high lifetime flower and fruit production). Under these conditions, one would expect to detect a positive genetically based correlation between investment in the two gametic types.
In contrast, outcrossing hermaphroditic species can exhibit strong sexual specialization, with some genotypes (or flowers) contributing to future generations primarily through seed production while others pass on their genes primarily through pollen production and export. Here, the potential for strong gender bias, in addition to the possibility that organs within flowers share limiting resources, might more easily lead to the expression of and maintenance of negative genetic correlations between male and female investment within populations.
Future Work: We plan to continue to evaluate the hypothesis that genetic correlations should evolve differently in selfing vs. outcrossing species by measuring genetic correlations in a suite of closely related species that differ in their breeding system. This will require continued labor-intensive artificial selection experiments and the use of molecular or allozyme data to verify selfing rates in natural populations.
Project 2: Genetic and environmental influences on life history, floral traits, and sex allocation in Raphanus sativus (Brassicaceae; wild radish): the instability of genetic parameters across environments.
The measurement of the heritability of fitness-related traits and the evaluation of the relationship between phenotype and expected fitness are the first steps toward determining the role of natural selection on these traits in a given population. Additionally, it's necessary to discover the degree to which heritable variation in individual fitness and fitness functions are constant in time and in space. This is simply because evolution by natural selection is a cumulative process, and evolutionary change (by natural selection) will only occur if the direction of selection is consistent over many generations.
Over the last decade, experimental and natural populations of wild radish (R. sativus L.) have been used by plant evolutionary ecologists, geneticists and pollination biologists as a model system in which to evaluate the strength and type of natural selection that operate on fitness-related traits under natural conditions. For the last ten years (on and off), I've been using this convenient and well-known species to evaluate a suite of questions concerning the nature of selection on a variety of life history and reproductive traits. These questions all relate to the issue of whether components of natural selection remain consistent from generation to generation, or whether, like many other population parameters (e.g., phenotypic means, variance, and population size), the direction and intensity of selection vary enormously in space and time.
For example:
(1) Does the expression of genetic variation in fitness-related traits in natural populations depend on environmental conditions? Are fitness functions environment-specific? If so, do Genotype x Environment interactions contribute to the maintenance of quantitative genetic variation in these traits?
To evaluate these questions, I have replicated seed families of known genetic background in different growing conditions to observe environmental effects on the magnitude of phenotypic and genetic variation in life history and reproductive traits. A primary objective of this work has been to determine the extent to which the heritabity of plant performance, phenotype, and patterns of sex allocation are constant across environments. This common garden approach has proven to be an effective way to measure the effects of population density on the expression of genetic variation in the age of reproduction, flower size, pollen production, pollen size, ovule production, and seed mass; some of the results of this work are summarized in several papers (Mazer and Schick, 1991a, 1991b; Mazer, 1992; Mazer and Wolfe, 1993).
One striking result is that the magnitude of the genetic component to phenotypic variation in almost all of the characters we have investigated depends strongly on the density at which seeds are initially planted. If this is a general property of natural populations, then evolutionists' ability to detect or to predict the rate of evolution by natural selection in the field will depend critically on the local environmental conditions sampled by the investigator and on the range and frequency of environments occupied by a given population.
We have also discovered that, in wild radish, gender allocation is strongly modified by environmental conditions (specifically, plant population density). In this species, components of female reproduction (the number of ovules per flower, the proportion of ovules that develop into seeds, the number of seeds per fruit, and mean individual seed mass) are much more sensitive to population density than is pollen production per flower or pollen grain size. Female components of reproduction per flower and fruit decline drastically with increasing population density, while pollen production per flower and pollen size remain relatively buffered against environmental change. I have suggested that this gender-specific response to stress may in fact be adaptive, depending on the patchiness of the landscape (Mazer, 1992). Under stressful conditions, genotypes which preferentially invest in the gametic type that is more likely to disperse a long distance (i.e., pollen) - thereby escaping local, unfavorable microhabitats - may have higher long-term fitness than genotypes that preferentially invest in the gamete with relatively short dispersal distances.
Future work: The development of molecular markers in wild radish
makes it possible to determine the distance of gene flow through
pollen vs. seeds. This tool - which I hope to use in future work
on wild radish - would allow a test of the hypothesis that, under
locally stressful conditions, male-biased genotypes have higher
individual fitness than female-biased genotypes.
(2) Are heritable characters genetically linked, and, if so, are correlations consistent across environments? Moreover, do such character correlations represent a "constraint" on the direction or rate of evolution by natural selection or are they the adaptive outcome of selection?
For several reasons, evolutionists are intensely interested in the degree to which characters influencing reproductive success are genetically linked. First, if traits are strongly linked, they may not evolve independently; selection on one character will influence the evolution of correlated characters. Such genetic correlations, and the evolutionary "constraints" they are thought to impose, may impede the evolution of a given character even if its phenotype strongly influences survivorship or reproduction. Consequently, genetically based correlations among characters hold implications for microevolutionary change involving combinations of traits, for population divergence, and for the process of speciation. Within populations, for example, strong genetically-based correlations due to pleiotropy or linkage are often thought to impose limits on the independent evolution of the correlated characters. At a higher level, strong genetic correlations between characters within species may determine or limit the nature of phenotypic divergence among populations during the speciation process. For example, a significant negative correlation between ovule number per flower and flower diameter among genotypes of Primula stricta appears to be mirrored among Primula species means (Mazer and Hultgard, 1993), potentially reflecting such a genetic constraint acting during the speciation process.
A second motive for measuring genetic covariation among reproductive characters is to evaluate the proposal that genes with pleiotropic effects can (under certain conditions) maintain genetic variation in fitness-related traits. Moreover, the repeated detection of particular genetic correlations among traits within species - for example, the commonly observed negative correlation between pollen size and pollen production per flower - and strong patterns of character covariation among species (e.g., the positive correlation between flower size and the pollen/ovule ratio among angiosperms) suggest the presence of non-random associations of trait values that result in alternate phenotypes of equal long-term fitness. In these cases, the presence and persistence within populations of alternate trait combinations suggest that natural selection has operated to maintain these genetic correlations.
Finally, while theoretical work in resource allocation and quantitative genetics predicts that negative genetic correlations should be common in nature, the results of available empirical studies are sparse and often equivocal. Our ongoing work with wild radish and sand-spurrey aims to help fill this gap.
In addition to providing quantitative estimates of the strength and nature of correlations among traits, these wild radish studies will provide estimates of the degree of genetic control over phenotypic plasticity in pollen production and size, flower size, ovule production, gender expression, lifetime seed production and seed mass.
Ongoing and Future Work: In an effort to address the question, "Is plasticity adaptive?", we are also measuring the degree to which the expression of phenotypic plasticity or maternal effects in life history or reproductive traits influences expected fitness over a range of population densities. For example, preliminary results suggest that maternal families that respond to low population density by producing relatively large seeds suffer a fitness deficit under high-density conditions, where they produce relatively small seeds. This pattern suggests that there may be a "cost" to the ability to respond to environmental conditions by altering allocation to offspring.
II. The Detection of the Long-term Outcome of Natural Selection and the Ecological Sorting of Species Among Habitats: Comparative Studies of Plant Reproductive Characters
One way to examine the long-term role of natural selection in molding plant reproductive characters is to use a comparative approach. That is, one examines the joint distribution across an array of species of character states (for the trait[s] of interest) and an environmental attribute. A related method is to make explicit use of phylogenetic relationships among species in order to evaluate:
These methods are non-experimental in nature, but they have been extremely successful in elucidating the ecological importance or function of life history and reproductive characters in plants and animals.
I have used a comparative approach to detect and to evaluate the statistically subtle ecological and evolutionary associations between seed size, life history and habitat attributes among hundreds of temperate zone species (see Mazer, 1989, 1990). In addition, I have explored the ecological significance of allometric relationships involving fruit size, shape and composition (fruit pulp mass to seed mass ratios) at several developmental and taxonomic levels including: ontogenetic patterns; within-species relationships; associations among related species (within the Lauraceae); and patterns among unrelated species (at the level of plant communities) (Mazer and Wheelwright, 1993). Finally, I recently examined with Dr. Bruce Tiffney (UCSB) the association between taxonomic diversification and dispersal mode among hundreds of angiosperm genera and families (Tiffney and Mazer, 1995). These broad-scale comparative studies lend a perspective not attainable from detailed population or genetic studies within species.
III. Adaptations of Fruits, Seeds, and Taxa to Lowland Tropical Rainforest Habitats: Manu National Park, Peru, and the Biological Dynamics of Forest Fragments Project, Manaus, Brazil
Project 1: Habitat and Floristic Heterogeneity in in a Lowland Rainforest
From 1987 - 1993, as a Research Collaborator at the National Museum of Natural History, I participated in the Smithsonian's Biological Diversity Program. This research program established a biological station in Manu National Park, the largest tropical rainforest reserve in Peru (over 1,800,000 hectares). Several thousand species of angiosperms live in the park, and many are economically important species of which the reproductive biology and ecological requirements in nature are poorly known. To protect the wildlife and flora of this remote wilderness, Manu National Park was established in 1973, when a total of 1,532,806 hectares were set aside. Since this time, UNESCO declared the area as a "Biosphere Reserve", which now comprises 1,881,200 hectares divided into three zones which differ in their degree of use for tourism, research and settlement. Approximately 1,530,000 hectares are protected in their natural state with no human interference (the Core Zone); 257,000 hectares are available for limited tourism and research (the Buffer Zone), and the remaining 91,000 hectares are available for human settlement (the Cultural Zone). The BIOLAT field station has been established in the Buffer Zone at the site of the Park Guard Headquarters, Pakitza.
The main goal of my research in Manu was to detect ecological factors that influence the distribution of the dominant tree species among dissimilar but adjacent habitat types. I conducted a three-year study of soil quality and leaf litter accumulation in different rainforest sites and habitats (Mazer, 1996, in press); this work suggests that habitats (e.g., terra firma vs. floodplain) differ in the rate of decomposition (by microorganisms and fungi) faced by dispersing seeds and young seedlings, a factor that may influence the distribution and abundances of adult tree species.
The work in Manu has motivated me to seek evidence for adaptations of fruits and seeds to terra firma vs. floodplain habitats. I am now working on a photographic field guide (to be co-authored by Ing. Fernando Cornejo) to the fruits and seeds of Peruvian lowland neotropical rainforest habitats from the Madre de Dios region (southeastern Peru). To date, we have completed a one-year period of fruit and seed collecting and photography at a research site on the Tambopata River, near Manu National Park. This field work was followed by a year of herbarium and lab work; our expected date of completion of the book is June, 1998. We have collected, identified, photographed, and prepared voucher specimens of over 1000 species (including more than 100 families and 500 genera) that will be included in the Field Guide, and I plan for many of the images soon to be available on the World Wide Web.
Future Work: My long-term goal is to evaluate adaptations of fruits
and seeds (involving modes of dispersal, germination behavior,
secondary chemistry, and morphology) that belong to species restricted
to particular rainforest habitats.
Below are a few samples of our fruit and seed images. Please note that
in the images of highly magnified seeds and fruits, the smallest units of the scale are millimeters. Please forgive all imperfections; this section is still under construction!
Mendoncia glabra (Poeppig) Nees (Acanthaceae)
Press for a view of Mendoncia hirsuta (Poeppig) Nees (Acanthaceae)
Press for a view of Tapirira guianensis Aublet (Anacardiaceae)
Press for a view of Ormosia nobilis Tulasne (Fabaceae)
Press for a view of Pterocarpus rohrii M. Vahl (Fabaceae)
Our photographs of fresh fruits - as seen below - were taken in the field (at the Tambopata
Wildlife Reserve, Madre de Dios) over a 12-month period. To save film, photographs
include the images of fruits representing 1 - 5 species that were producing fruit at the same
time. These photographs will be digitized and editted to provide separate, single-species
images for publication and/or continued display at this web site.
The species shown in the image above include: Heliconia stricta Huber (Heliconiaceae: blue-fruited infructescence with bright orange bracts); Randia armata Swartz DC. (Rubiaceae: yellow-green, round fruit); and Vigna luteola Jacquin) Bentham (Fabaceae: dark legumes).
Click for a view of Marsdenia macrophylla (Humboldt & Bonpland ex Schultes) Fournier
For a view of Passiflora stricta Huber (Passifloraceae: large green fruit) and Melothria dulcis Wunderlin (Cucurbitaceae: bright yellow, round fruit) Press Here
For a view of Lacmellea peruviana (Van Heurck & Muell. Arg.) Markgraf (Apocynaceae: yellow/green oblong fruits, lower right corner); Bactris simplicifrons C. Martius (Arecaceae: infructescence with 5 yellow/orange fruits); Ruellia sp. C. Martius (Acanthaceae: green fruits, lower center); Pseudolmedia laevis (R. & P.) J. F. Macbride (Moraceae: pair and cluster of bright red fruits, upper left corner); Maietia guianensis Aublet (Melastomataceae: spiked green/black fruits, lower left corner) Press Here
For a view of Endlicheria dysodantha (Lauraceae: upper right corner); Solanum barbeyanum Humber (Solanaceae: pair of bright yellow, oblong fruits); Pseudolmedia laevigata Trecul (Moraceae: four reddish fruits, lower left corner) Miconia prasina (Swartz) DC. (Melastomataceae: cluster of dark blue to light green fruits); and Borismene japurensis (C. Martius) Barneby (Menispermaceae: oblong, orange fruits) Press Here
Project 3: The Effects of Forest Fragmentation on the Ecology and Distribution of Palms
This field study was designed in collaboration with Dr. Aldicir Scariot (a graduate student in my research group) to provide a preliminary test of several predictions derived from Island Biogeography Theory as applied to a fragmented tropical rainforest landscape. Using the Biological Dynamics of Forest Fragments Project research site near Manaus, Brazil, the effects of the short-term isolation (10-15 years) of forest fragments on components of palm diversity, abundance, and demography were measured and evaluated in a total of 11 reserves of four size classes (1-hectare, 10-ha, 100-ha and continuous forest). This project had three main objectives. The first goal was to provide quantitative measures of the composition, species richness, and species diversity of the palm community in forest fragments of different sizes and adjacent intact continuous forest. The second objective was to evaluate the effect of forest fragmentation on seedling, juvenile, and adult densities for the entire palm community, for common and rare species as distinct groups, for each forest stratum (canopy, midstory, and understory), and for each individual palm species. The third aim was to estimate the effects of physical damage on seedling mortality across reserve sizes in order to determine whether this process contributes to the demographic differences observed among fragment sizes. A total of 23,225 individuals representing 36 species of palms were monitored. While the number of palm species per hectare currently surviving as adults in the monitored plots did not differ among reserve sizes, the smaller forest fragments had fewer and different palm species in the seedling life stage than the continuous forest, revealing that palm populations are most sensitive to fragmentation in the seedling stage. The groups of common species (21 species) and rare species (10 species) each had lower population densities in the smaller fragments than in the 100-hectare or continuous forest reserves. All forest strata similarly presented a trend of declining palm population densities as reserve size decreased. Eight of the 21 common species were negatively affected by reduced reserve size; one species alone showed a significant increase in density in the small fragments. An experiment using artificial seedlings was also conducted to evaluate the effects of physical damage on seedling persistence in forest fragments of different sizes. The 10-ha forest fragment in one of the three sites had significantly lower seedling survival curves over year compared with continuous forest. Over all sites and after one year, seedling mortality caused by litterfall was much higher in the 1- and 10-ha reserves than in the continuous forest. In sum, it is clear that in the short period of time since these forest fragments were established, the demographic effects of fragmentation are already detectable, at least in the seeding stage. Nevertheless, if density-dependent mortality occurs among the seedlings, this could obscure the pattern of fragment-size-dependent palm densities. These results hold several implications for rain forest conservation and reserve management, but precise predictions concerning the longterm outcome of forest fragmentation on species diversity and local population persistence require more detailed studies of the ecological processes that may differ among forest fragments of different sizes.
Selected Publications
Mazer, S. J. 1989. Ecological, taxonomic, and life history correlates of seed mass among Indiana Dune angiosperms. Ecological Monographs 59: 153-175.
Mazer, S. J. 1989. Genetic associations among life history and fitness components in wild radish: controlling for maternal effects on seed weight. Canadian Journal of Botany 67: 1890-1897.
Mazer, S. J., R. R. Nakamura and M. L. Stanton. 1989. Seasonal changes in components of male and female reproductive success in Raphanus sativus L. (Brassicaceae). Oecologia 81: 345-353.
Mazer, S. J. 1990. Seed mass variation of Indiana Dune genera and families: taxonomic and ecological correlates. Evolutionary Ecology 4: 326-358.
Byrne, M. and S. J. Mazer. 1990. The effect of position on fruit characteristics, and relationships among components of yield in Phytolacca rivinoides (Phytolaccaceae). Biotropica 22: 353-365.
Mazer, S. J. and C. T. Schick. 1991. Constancy of population and genetic parameters for life-history and floral traits in Raphanus sativus I. Norms of reaction and the nature of genotype by environment interactions. Heredity 67: 143-156.
Mazer, S. J. and C. T. Schick. 1991. Constancy of population and genetic parameters for life-history and floral traits in Raphanus sativus II. Effects of planting density on phenotype and heritability estimates. Evolution 45: 1888-1907.
Mazer, S. J. 1992. Environmental modification of gender allocation in wild radish: consequences for sexual and natural selection. In Robert Wyatt, ed.), Ecology and Evolution of Plant Reproduction: New Approaches. Chapman and Hall. pp. 181 - 225.
Mazer, S. J. and L. M. Wolfe. 1992. Density influences the expression of genetic variation in seed mass in wild radish (Raphanus sativus: Brassicaceae). American Journal of Botany. 79: 1185-1193.
Mazer, S. J. and U. Hultgård. 1993. Variation in gender allocation and covariation among floral characters within and among four species of northern European Primula. American Journal of Botany. 80: 474-485.
Mazer, S. J. and N. T. Wheelwright. 1993. Fruit size and shape: allometry at different taxonomic levels in bird-dispersed plants. Evolutionary Ecology. 7: 556-575.
Delesalle, V. A. and S. J. Mazer. 1995. The structure of phenotypic variation in gender and floral traits within and among populations of Spergularia marina (Caryophyllaceae). American Journal of Botany 82: 798 - 810.
Tiffney, B. H., and S. J. Mazer. 1995. Angiosperm growth habit, dispersal, and diversification reconsidered. Evolutionary Ecology 9: 93 - 117.
Mazer, S. J., and D. L. Gorchov. 1996. Paternal effects on progeny phenotype: distinguishing genetic and environmental causes. Evolution. 50: 44 - 53.
Mazer, S. J. and V. A. Delesalle. 1996. Temporal instability of genetic components of floral trait variation trait: maternal family and population effects in Spergularia marina (Caryophyllaceae). Evolution 50: 2509 - 2515.
Delesalle, V. A., and S. J. Mazer. 1996. Effects of nutrient levels and salinity on floral trait expression in Spergularia marina (Caryophyllaceae). International Journal of Plant Sciences 157: 621 - 631.
Mazer, S. J. and V. A. Delesalle. 1996. Floral trait variation in Spergularia marina (Caryophyllaceae): ontogenetic, maternal family, and population effects. Heredity 77: 269 - 281.
Mazer, S. J. 1996. Leaf litter accumulation, decomposition, and soil quality within and among flood plain and terra firme habitats in the vicinity of Pakitza, Peru. Smithsonian Institution Biological Diversity Program Research Volume. In press.
Machon, N. , M. Lefranc, I. Bilber, S. J. Mazer, and A. Sarr. 1996. Allozyme variation in Ulmus species from France: analysis of differentiation. Heredity, in press.
Mazer, S. J. and V. A. Delesalle. 1996. Floral trait covariation in Spergularia marina (Caryophyllaceae): temporal and geographic variation. Journal of Evolutionary Biology, in press.
Mazer, S. J. and V. A. Delesalle. 1996. Genetic correlations among
sex allocation traits within selfing and outcrossing species:
evolutionary predictions and preliminary observations. Evolutionary
Ecology, in press.
