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biol 4120 principles of ecology lecture 8 the distribution and spatial structure of populations n.
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  1. BIOL 4120: Principles of Ecology Lecture 8: The Distribution and Spatial Structure of Populations Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

  2. Chapter 10 • Population and Subpopulations (or local populations) Due to environmental heterogeneity and mosaic of different habitats, many populations are divided into smaller subpopulations.

  3. Properties of Population Most important property is abundance of population which is determined by its distribution and density. Populations have Distribution: population extent, geographic area occupied by a population (also called geographic range) Population size: Number of individuals in a population (varies with food supplies, predation rates etc.) Population Structure: encompasses a number of attributes, including density and spacing of individuals within suitable habitat and proportions individuals of each sex and age class (Spatial structure) Density: How to determine population density? Age structures and Different sex ratios along time

  4. Topics 10.1 Populations are limited to ecologically suitable habitats 10.2 Ecological niche modeling predicts the distributions of species 10.3 The dispersion of individuals reflects habitat heterogeneity and social integrations 10.4 The spatial structure of populations parallels environmental variation 10.5 Three types of models describe the spatial structure of populations

  5. 10.1 Populations are limited to ecologically suitable habitats • Distribution • Spatial location, Area over which a species occupies • Geographic range • Area that encompasses the entire population of a species • Limited by • Climate: temperature, precipitation… • And other factors • Food production • Water supply • Habitat • Incidence of parasites, pathogens and competitors • Geographic barriers All these factors together are called ecological niche

  6. The distribution of a species is related to ecological niche • Fundamental niche: The range of physical conditions over which species can persist • Realized niche: Within the range of conditions, predators, pathogens and competitions limit the distribution of a species to a smaller place

  7. Barnacles

  8. Distribution of a species varies at different spatial scales Distribution of moss Tetraphis Continental scale: climate suitability Particular area: microclimate and stream banks (coniferous trees and abundance) Within a particular locality: occupy stumps of conifer trees (pH is acidic) Local subpopulations

  9. BIOL 4120: Principles of Ecology Lecture 8: The Distribution and Spatial Structure of Populations Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

  10. Recap Population & Metapopulation Populations properties Distribution, size, and structure (density, spacing, age, sex etc) Niche: Fundamental niche Realized niche Distribution patterns at different scales

  11. Distribution of the perennial shrub Clematis Only in Jefferson county, Missouri Dry and rocky soils Further confined to suitable soil structure, moisture and nutrients

  12. Individual fitness is highest within the natural distribution of a species A transplant study by Amy Angert et al. of Michigan State University Two species of monkeyflower, one grows in low and one in high elevations

  13. Other factors influence species distributions • Dispersal limitation • Migration

  14. Dispersal limitation • Dispersal: movement of individuals in space. Dispersal limitation: the absence of a population from suitable habitat because of barriers to dispersal Methods of dispersal Passive dispersal (gravity, wind, water, animal) seeds of plants, small animals, fish, shrimp. fruits and seeds ate and carried by animals (long distances) Active dispersal: animal movement. Barriers to long-distance dispersal often limit geographic ranges are overcome by human intervention Move plants and animals around the world (invasive species)

  15. Migration Geographic range of a population includes all the areas of its members occupy during their entire life history Migration – A round trip, perhaps involving mating Red-necked ducks: Breeding in the northeast Winter in South Carolina and Florida Gray whale: Winter in California, Summer in Arctic Migratory pathways of Ring-necked ducks and gray whale.

  16. Atlantic bluefin tuna range across the breadth of the Atlantic Ocean (A 5 year record of the movement of a single individual using electronic tag) Some fish (Actic Terns) travel 30,000 km per year Tuna: Tagged in 1999 and captured in 2003

  17. Wildebeests in East Africa migrate long distances following the geographic pattern of seasonal rainfall and fresh vegetation

  18. Some migratory movements are a response of occasional failure or depletion of local food supplies (Somalia, Africa, 1962) e.g.: migratory locusts

  19. 10.2 Ecological niche modeling predicts the distributions of species • How to predict the species distribution? • For ecological management purposes (species protection, conservation, new species introduction), we need to understand and predict species distribution • Ecological niche modeling: Using exist species distribution knowledge and the related climatic factors to predict actual or potential species distribution under future climate conditions

  20. Ecological niche modeling The catalog of ecological conditions is a species’ecological envelope. Mostly involve “training” and “test” sites. Also called Climatic Envelope Modeling

  21. Ecological envelopes of three species of Eucalyptus trees across 6,080 plots in southeastern New South Wales, Australia

  22. Ecological envelopes can be used to predict the distributions of invasive species Aquatic plant (Hydrilla) and Chinese bush clover (Lespedeza) Native regions in Asia and new location in US

  23. Global warming on the distribution of Anchovies: expanding their geographic ranges northward increased species richness in North Sea Hiddink and ter Hofstede 2008 Increased species diversity, but decreased some commercial species.

  24. 10.3 The dispersion of individuals reflects habitat heterogeneity and social integrations • Dispersion • The spacing of individuals within respect to one another within the geographic range of a population Not dispersal

  25. Distribution patterns • Distribution patterns 1. Random: Equal chance of being anywhere. Neutral interactions. 2. Uniform (spaced) distribution of resources. Regular: Uniformly spaced. Exclusive use of areas. Antagonistic interaction individuals avoid one another. 3. Clumped: Unequal chance of being anywhere. Mutual attraction between individuals. Patchy resource distribution.

  26. Clumped distribution of Aspen trees Different clones of aspen trees, distinguished by timing of leaf fall. Each clone from one seed

  27. 10.4 The spatial structure of populations parallels environmental variation Population density Number of individuals per unit of area Variation in population density Population density of a small songbird of prairies and grasslands: dickcissel Highest at the center of a species’ geographic range

  28. Influenced by available habitat • Carolina wren: Northwards -7oC; Westward>52mm • When all environmental factors within its range of tolerance, the organism can live in its habitat • Horned lark • Avoids forests • Available territory

  29. Recap Populations are limited to ecologically suitable habitats Dispersal and migration Spatial patterns Ecological niche modeling predicts the distributions of species Ecological niche model The spatial structure of populations parallels environmental variation

  30. Ideal free distribution hypothesis All individuals seek good patch and good patch filled up quickly and eventually, becomes less favorable than poor patch. The quality of these good patches decreases until poor patches become equally good choices. In the end, individuals move from better to poorer patches until each patch has the same value for individual fitness, regardless of the intrinsic patch quality.

  31. Dispersal from high-density to low density patches Population distribution rarely reach Ideal Free Distribution 1. individuals do not know which patches are good patches 2. dominant individuals may forces subordinates to leave high-quality patches Results: individuals in best habitats produce surplus individuals whereas in poor habitats, deaths exceeds births and populations can’t maintain their numbers

  32. Dispersal from high-density to low density patches Immigration from good to poor patches One example: Blue tit (Parus caeruleus), a small songbird Two habitats: Deciduous downy oak, more caterpillars as food, high density (90 pairs/100 ha), high reproduction (5.8/pair) Everygreen holm oak, low density (10 pairs/100 ha), low reproduction (3.6 /pair) Immigration maintain poor patch subpopulations (otherwise, 13% decrease).

  33. Even with dispersal, population distribution can not move to very poor habitat

  34. 10.5 Three types of models describe the spatial structure of populations

  35. 10.6 Dispersal is essential to the integration of populations When individuals disperse throughout a population, they link different subpopulations together and make the whole population function and evolve as a single structure. When dispersal is limited, different subpopulations behave independently to each other. Measurements of dispersal: Method: mark and recapture Life time dispersal distance: how far an individuals move, on average, from their birthplace to where they reproduce. Life time dispersal area: Neighborhood size: number of individuals, defined by the life time dispersal area times the population density. An example, 8 small songbird species: Life time dispersal distances: 344 to 1,681 meters Population densities: 16 to 480 individuals per sq. km Neighborhood size: 151 to 7,697 individuals

  36. Neighborhood size= lifetime dispersal area * population density Since the average dispersal distance bears a constant relationship to population density, neighborhood sizes are rather more similar than one expect from either dispersal distance or population density alone: land snails: 1,800 to 7600; songbirds: 151 to 7679; lizard: 225 to 270.

  37. Introduced population can spread rapidly outside their established range European starling in the US (shade area: breeding range; dots: records of birds, young individuals)

  38. Invasive species Gypsy moth caterpillars Defoliated oak forest $764 M loss in 1981

  39. Invasive species Kudzu, an invasive species Native to Asia, introduced to US as an ornamental vine in 1876 Used to control soil erosion in 1930s and 1940s 1950s, recognized as pest Cover southeastern US, 2 million to 7 million acres

  40. 10.7 Macroecology addresses patterns of range size and population density Macroecology: study of relationships between organisms and environments at large spatial scales; to determine and explain the distribution patterns and population size of a particular species by large samples of species.

  41. Macroecology addresses patterns of range size and population density James Brown, University of New Mexico Distribution and population size of a species reflects the distribution of conditions to which individuals of the species were well adapted. If these conditions are common and widespread, then the population should be common and wide-spread.

  42. Range size and population density Birds with large ranges tend to have higher maximum abundances (457 species of North American birds) (McGill and Collins, 2003)

  43. Body size, distribution, and abundance Population density to body size, a matter of size relative to space Sample of herbivorous mammals, slope is -0.73. (Gaston and Blackburn 2000)

  44. One example: Population density in carnivores is closely related to their body size The density of population decreases as the -2/3 power of body mass of predator. (Carbone and Gittleman 2002)

  45. Energy Equivalent Rule Concept: Populations tend to consume the same amount of food per unit of area regardless of the size of individuals Metabolic rate of organisms and therefore, their food requirements, increase with body mass, to a power of 3/4. Since the population density decreases with the body mass at the same rate that food requirement increases. The total food consumption of a population per unit of area is equal to the average consumption per individual multiplied by the local population density (M3/4 * M-3/4=1). Therefore, elephants and mice would have about the same food requirement per hectare, and by implication, they would have similar effects on population and ecosystem processes.

  46. 10.8 Variation in populations over space and time Distribution of crop damage caused by chinch bugs in Illinois varied dramatically over the period between 1840 and 1939. Yellow: low density of chinch bugs Blue: high density Reasons: climate change, resources, predators and pathogens? Population density change over time and space

  47. The END