Human-caused disturbances, such as landscape fragmentation and alteration, loss of dispersal agents, and global warming, require that plant populations be able to disperse both genes and individuals to new sites. We introduce an innovative approach to the study of seed flow, based on molecular genetic analysis of maternal tissue in the seed coat, by analyzing the seed pool structure of sets of seeds dispersed across a landscape. We will apply this novel analysis to seed dispersal of a threatened tree species, California valley oak, by the acorn woodpecker. We have two objectives: (1) to conduct novel theoretical work on the statistical model that allows hypothesis testing on seed dispersal under different circumstances; (2) to examine the seed pool structure and dispersal distances of seeds found in acorn woodpecker storage sites, and recruits in natural seedling patches.
This research makes several valuable contributions. (1) It develops methods for studying seed dispersal that are applicable to a wide range of species, including those experiencing landscape change and loss of vertebrate dispersers. (2) It contributes to a growing discussion by ecologists and population genetics about the shape of the seed dispersal distribution. (3) Results from this study will be included in several K-12 environmental workshops, meetings with policy-makers, nd state and federal scientists.
This NSF proposal was a supplement to ongoing, and particularly productive project, with a slight change in emphasis. The original proposal had dealt with developing and using new statistical-genetic methods for the study of gene flow across an extended landscape, under a variety of circumstances. We began with a study of Valley oak from the savanna of California, and showed that seed movements from the mother tree were typically very short, a few meters by small mammals, perhaps a couple of hundred meters by birds. In contrast, pollen movement (by wind) could be measured in hundreds of meters to over a kilometer. We showed that overall genetic pattern among new recruits was striking over 500 meters, due largely to restricted seed flow, but that the pollen flow was extensive enough to "smoothe out the bumps" and providing some "genetic glue" to hold the species together over very long distances. Our methods were new, and a variety of colleagues from around the world wanted to ask similar questions about their own species of interest. We quickly became involved in similar studies with other oak species in California, Missouri, Spain and Denmark. The methods were general enough that we also found ourselves collaboratiing with colleagues in Costa Rica on legumiinous tree species (Enterolobium and Albizia), with colleagues in Argentina on South American hardwoods (Nothofagus, Embothrium) and conifers (Araucaria and Austrcedrus), and with colleagues in the US and Spain (Pines). We have also collaborated with people working on shrubs and herbs (Heliconia in Brazil and the Carribean, Dieffenbachia in Mexico), and coaching others on methodology for a variety of other organisms. It quickly became apparent that similar methods could be used with animals, normally tracked with radio collars or small transmitters (deer, moose, birds, etc.), but sometimes using genetic markers instead, and we were drawn into studies of bees and wasps and the pollen they carry, ticks and the bacterial diseases they carry, pelagically distributed limpets and starfish, where larvae move hundreds of kilometers across the ocean. By the time the Supplement was approved, it had become clear that some of the same methods could be used for taxonomic diversity, measured at the species level in a communty. In that regard, population genetics had always relied (almost exclusively) on describing variation in "variance" terms, but population ecologist had couched their analytical methods in terms of "diversity" instead. It has recently become clear that while these two approaches are philosophically a bit different, one can translate back and forth between them computationally, and without much difficulty. They turn out to be two different ways to think about the same phenomena; we have developed methods to "move back and forth" between those different methodologies; and the translations have been productive for several organisms. Working again with colleagues, we have deployed the dual translation to Australian orchids, New Zealand sphagnum mosses, fungal pathogens of US and Canadian blueberry crops, and have been coaching other colleagues on communities of pollinating bee species for agricultural crops, mosquito disease vectors, invasive grasses, and numerous other organisms. It develops that gene flow across the landscape, or animal migration and movement across that same landscape, often with the animals carrying the plant propagules, can be described in the same mathematical biodiversity framework, . We have been developing the formal translation of both phenomena, using a variety of organisms to make the connection producitve: limpets and starfish, spread across the Pacific, birds/bats and the fruits they eat (and spread) in California, Brazil and Mexico; orchids and pollinating wasps in Australia. In the process of working out the translation between "variation-speak" and "diversity-speak", we are beginning to cross the boundary between evolutionary genetics and ecology. What lies ahead is a more productive understanding of evolutionary biogeography. We have initiated a large study, in collaboration with an Argentine colleague, working on the abiotic (climatic and geographic) correlates of both morphological and genetic pattern of Embothrium (a small tree) across the southern third of the Andes, using traditional statistical methods and newly developed methods of our own. We have shown that morphological and genetic pattern across this extended landscape are basically two-dimensional (annual temperature/precipitation, and summer-vs-winter seasonality), a pattern that runs WNW to ESE along (on both sides of) the Andes. Primary diversification over geography is a climatic consequence, but genetic isolation is also evident, due to limited exchange over vast distances. We developed a new method of translating predicted climatic patterns , as a consequence of climate change, and have used that to predict where Embothrium can be expected to persist on the landscape, several decades in the future, and what it will "look like" (morphologically & genetically) in its new locations. It will move with the climate, though it won't have to move very far, and we can expect it to persist.
