Plant Population Ecology -Data Overview General objectives and questions addressed Key people Some terms Basics of plant life cycle Dispersal, Dormancy and recruitment Neighborhood effects and thinning Herbivory Reproduction Survey of recent papers - topic coverage Objectives of plant population biology: What are the relative magnitudes of effects of ecological and genetic factors in demographic changes in plant populations? How do animal interactions (herbivory, pollination, seed dispersal) affect demographic changes in populations and lead to differences between life history characteristics of populations? How do alternative dormancy and dispersal characteristics affect population dynamics? How are plant size distributions related to age distributions and how do these interact with localized spatial heterogeneity? What are the effect of plant defensive mechanisms on popualtion dynamics in the presence of predators/herbivores? How does the demography of plant parts relate to whole plant and population response? People (a few): Janis Antonovics - plant population genetics A. D. Bradshaw - Phenotypic plasticity J. J. Burdon - plant pathogen interactions Frederick Clements - 1929 text on Plant Competition M. D. Gadgil - dispersal and selection John L. Harper - founder of modern plant population biology K-I. Sakai - competition Jose' Sarukhan - plant demography A. G. Tansley - A founder of vegetation science Patricia Werner - demography of teasel C. T. de Wit - competition and growth models Some references: Papers to read: Fowler, N. L. 1995. Density-Dependent Demography in Two Grasses: A Five-Year Study. Ecology 76:2145-2164. Lonsdale, W. M. 1990. The Self-Thinning Rule: Dead or Alive? Ecology 71:1373-1388. Schemske, D. W. et al. 1994. Evaluating approaches to the conservation of rare and endangered plants. Ecology 75:584-606 References: Dirzo, R. and J. Sarukhan. 1984. Perspectives in Plant Population Ecology. Sinauer, Sunderland, MA. Harper, J. L. 1977. Population Biology of Plants. Academic, London. Some Terms: Allelopathy - adeverse influence exerted by one strain of plant over another of the same species by production of a chemical inhibitor, often terpenoid or phenolic Autecology - the study of the ecology of any individual species Clone - organisms all dervied from a single progenitor by asexual means Dormancy - life stage of temporarily reduced metabolic activity Genet - an individual plant grown from one sexually-produced seed or all the individuals produced by vegetation reprocution from one such plant Iteroparous - capable of reproducing many times Monocarpic - dying at the end of its first fruiting season as do annuals, biennials and some perennials Phenotypic plasticity - ability of a individual to display different phenotypic characteristics depending upon conditions during growth Polycarpic - potentially able to fruit many times Ramet - any physically and physiologically independent individual plant, grown either from a sexually-produced seed or from vegetative reproduction Relative growth rate (RGR) - (ln(W(t2)) - ln(W(t1)))/(t2 - t1) where W(t) is dry weight of plant or plant part at time t Secondary compound - metabolites which do not function in the biochemical activities which support growth (e.g. photosynthesis, respiration, protein synthesis) - includes alkaloids, flavonoids, terpenoids which may function in plant defense Self-thinning - density-dependent mortality in plant populations such that population density decreases as plant size increases Semelparous - reproducing once in its lifespan Synecology - the study of the relationships between communities and their environment Plant Life Cycle: Seed bank in soil - recruitment of seedlings - growth in mass and numbers of plant modular units - seed production Processes affecting within-population dynamics include genetic (frequency dependent and independent selection, outcrossing rate, inbreeding depression) and ecological (deensity dependent and independent effects, pollen limitation, demographic stochasticity, environmental stochasticity) A typical method to analyze plant life cycle effects on population-level processes is to break the population into comparments corresponding to seeds, seedlings, juveniles, adults - sometimes these are related to plant size (biomass, leaf number, etc.) Dispersal Gadgil pointed out that dispersal may limit population sizes due to: (i) Availability of sites for germination are few (ii) habitable areas are too far apart relative to the dispersal capabilities of the species (iii)carrying capacity of the habitable sites is low (iv) time for which sites are suitable is too short relative to the dispersal rate of the species (v) habitability of a site is too short (e.g. successional displacement is rapid) (vi) colonization and full exploitation of carrying capacity of a site is low Seed dispersal distances are affected by mode of dispersal (wind, water, animal, plumes, wings, etc.), and activity of dispersing agent (wind speed, animal presence) Dormancy Typically occurs in the dispersal phase of plants Not only way plant can survive under adverse seasonal environmental conditions - alternative is seasonal dimorphism - two distinct growth phases adapted to different seasons (some desert shrubs which have large leaves for wet season and small leaves for dry season) Innate dormancy - seeds born dormant, viable but not capable of germinating under good conditions when released from parent Induced dormancy - acquired dormancy - inability to germinate due to some experience after ripening Enforced dormancy - inability to germinate due to an environmental constraint such as low water, low temperature, etc. Many studies on alternative dormancy patterns within particular communities - e.g. in Mojave desert some species germinate after summer storms (rare - occur every 5-20 years), some after normal winter rains, soem after November rains, and some which can germinate any time. Seed Bank Many places, the number of individuals present as dormant (seeds) is much higher than those which are actively growing. Some stimuli may be necessary to move a seed from dormant to active state. There are distinctive depth distributions for seeds and seeds may migrate vertically due to percolating rainfall and freezing and thawing and animal disturbance There are long term studies of seed bank dynamics to analyze relative losses due to fungal attack, predation, germination . Some generalizations: long-lived seeds are characteristic of disturbed habitats most long lived seeds are annuals or biennials small seeds tend to have greater longevity than large seeds seeds of mature tropical forests have very short lives Germination is greatly a function of microtopography, microclimate and conditions provided by a "safe site" with conditions to break dormancy, germination to occur and reesources for growth. Neighborhood effects and thinning Presence of a plant changes the environment of its neighbors, leading to potential for interference competition for resources, production of toxic compounds to limit neighbors, and changes in environmental conditions for neighbors (e.g. shading) There is a large literature on self thinning as a plant stand ages with w = k N^(-a) where w is average mass of a plant (grams), N is the plant density (number /m^2) and a and k are constants. There is a long history associated with assuming a =-3/2, giving the so called self thinning law. This supposedly holds for an even aged, crowded plant population and also for a interspecific stand. Another form is to let B= w N be the stand yield so B= k N^(1-a) Several recent careful statistical analyses of the available data indicate that the slope of this relationship is quite variable, and there may not be a power law relationship at all in many cases. Herbivory Defoliation effects on plants can depend on plant age, age of the plant parts consumed, may depend upon the plant density as well as the animal density, and plants have been shown to have mechanisms to minimize damage of defoliation and plants have a variety of buffering mechanisms to limit the efects of defoliation (increased efficiency of remaining leaves, new leaf flush, induced production of defensive compounds, etc.) Seed crops can have several roles in plant population: (1) the replacement of individual that die in a population (2) increase in population size locally (3) colonization of new areas a diostance from the parent (4) display of genetic variation Plants can escape from predation in time by having unpredictable seed production so predators cannot key on it, or when it occurs it is so large that the few predators do not greatly reduce it. Topics from 1990's search on plant population in 4 ecology journals: Summary: Modeling 6 Disease 7 Individual growth 1 Herbivory 16 Chemistry 2 Disturbance 6 Self-thinning 1 Size distributions 3 Competition 7 Reproductive success 11 Dormancy 1 Density dependence 3 Below ground issues 2 Plasticity 2 Spatial issues- dispersal 8 Demography 1 Clonal species 2 Invasive species 1 Establishment 2 Floral allocation 1 Total 83 Topics from Ann Rev since 1980 on plants 1. Measuring Fitness and Natural Selection in Wild Plant Populations Richard B. Primack, Hyesoon Kang 2. The Ecological and Genetic Consequences of Density-Dependent Regulation in Plants Janis Antonovics, Donald A. Levin 5. Phenological Patterns of Terrestrial Plants Beverly Rathcke, Elizabeth P. Lacey 6. A Unified Approach to Marine Plant-Herbivore Interactions. I. Populations and Communities Jane Lubchenco, Steven D. Gaines 7. Herbivores and the Dynamics of Communities and Ecosystems Nancy Huntly 8. Spatial Analysis of Genetic Variation in Plant Populations John S. Heywood 9. Pattern and Patchiness in Plant-Pathogen Interactions--Causes and Consequences J. J. Burdon, A. M. Jarosz, G. C. Kirby 10. Interactions Involving Plants, Homoptera, and Ants R. C. Buckley 11. Ecological Determinants of Genetic Structure in Plant Populations M. D. Loveless, J. L. Hamrick 12. Ecology of Seed Dispersal Henry F. Howe, Judith Smallwood 13. The Potential for Application of Individual-Based Simulation Models for Assessing the Effects of Global Change H. H. Shugart, T. M. Smith, W. M. Post 14. Architecture of Tropical Plants P. B. Tomlinson 15. Maternal Effects in Plants Deborah A. Roach, Renata D. Wulff 16. Seed Dispersal by Adhesion Anne E. Sorensen 17. The Evolution of Phenotypic Plasticity in Plants Carl D. Schlichting 18. Biological Aspects of Endemism in Higher Plants Arthur R. Kruckeberg, Deborah Rabinowitz 19. Resource Limitation in Plants--An Economic Analogy Arnold J. Bloom, F. Stuart Chapin, III, Harold A. Mooney 21. Herbicide Resistance in Weedy Plants: Physiology and Population Biology Suzanne I. Warwick 23. The Causes of Treeline George C. Stevens, John F. Fox 24. Fungal Endophytes of Grasses Keith Clay 27. Hydrophilous Pollination Paul Alan Cox 30. Tropical Rainforest Gaps and Tree Species Diversity Julie Sloan Denslow 33. The Role of Competition in Plant Communities in Arid and Semiarid Regions Norma Fowler 36. Morphogenetic Constraints on Patterns of Carbon Distribution in Plants Maxine A. Watson, Brenda B. Casper 39. The Ecology of Leaf Life Spans Brian F. Chabot, David J. Hicks 41. Evolution of Dioecy in Flowering Plants K. S. Bawa 42. Interactions Among Three Trophic Levels: Influence of Plants on Interactions Between Insect Herbivores and Natural Enemies Peter W. Price, Carl E. Bouton, Paul Gross, Bruce A. McPheron, John N. Thompson, Arthur E. Weis