Ch10 The Distribution and Spatial Structure of Populations2.pdf

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BIO120H © Lis| Page 111 chapter 10: THE DISTRIBUTION AND SPATIAL STRUCTURE OF POPULATIONS  fragmentation of habitat breaks them up into small passes  restricts mvmnt  isolated subpopulations in small habitats die due to loss of genetic diversity  species able to use disturbed habitats have become widespread  fragmentation also reduces habitat quality  more habitat edge  ex. trees at edge exposed to higher winds, die from excessive water loss  songbirds vs. brown-headed cowbird  cowbirds lay eggs in nests of songbirds  prefer open farms and fields  thus, they go into forest edges to search for host nests  nest parasitism reduces reproductive success of hosts  rodents also have ventured into forest edges, preying on eggs  population: consists of the indiv. of a species within a given area  live in areas of suitable habitat  patchy distribution of suitable habitat leads to divided pop.  subpopulations (local populations) subpopulations  pop. would move less frequently here than in homogeneous habitats  distribution (population extent): the geographic area occupied by a pop.  a.k.a. ggeographic rangeof a population  population size: the # of indiv. in a pop.  varies w/ food supplies, predation rates, nest site availability, other ecological factors  population structure: attributes of a pop. including   density and spacing of indiv. w/in a suitable habitat (spatispatial structure  proportions of indiv. of each sex and in each age class  spatial structure + pop. distribution present a pic of pop. arrangement in space  due to behavioural and physiological responses of indiv. to envmt POPULATIONS ARE LIMITED TO ECOLOGICALLY SUITABLE HABITATS  fundamental niche: the range of physical conditions over which species can persist  w/in the range of conditions, predators, pathogens, and competitors limit the distribution of a species to a smaller realized niche realized niche  envmtal conditions influence pop. abundance and dispersal by influencing birth, death, and dispersal  Clematis fremontii (perennial shrub)  distribution  climate restricts into a small area of the Midwestern US  the distinctive variety, riehlii occurs only in Jefferson County  Clematis fremontii var. riehlii’s geographical range  dry, rocky soils on outcroppings of limestone  2 species of monkeyflowers (Mimulus) living at diff. elevation in the Sierra Nevada of California  studied survival and reproduction w/in and outside natural elevation  lower-elevation indiv. (M. cardinalis) transplanted to plots w/in and above its natural elevational distribution  higher-elevation indiv. (M. lewisii) transplanted to plots w/in and below its natural distribution  survival, growth, and flower production higher in plots w/in normal ED  thus, species can sustain its pop.. only w/in the narrow range of envmtal conditions that make up its niche BIO120H © Lis| Page 211 Dispersal Limitation  presence/absence of a suitable habitat, barriers to dispersal, etc. have influence on pop. distribution  dispersal limitation: the absence of a pop. from a suitable habitat b/c of barriers to dispersal  ex. suitable habitats for sugar maples exist in Europe and Asia, but their seeds can’t disperse that far across the oceans to colonize  some of this limitation is destroyed by human intervention  introduced species  some indiv. have even crossed barriers themselves ex. to populate remote islands Migration  geographic range includes all areas a pop.’s members occupy during their life history  dwindling supplies of food promotes the long distance migrations of many species  irruptive behaviour (outbreaks) of i.e. migratory locusts from areas of food depletion ECOLOGICAL NICHE MODELING PREDICTS THE DISTRIBUTIONS OF SPECIES  the more suitable the conditions for a species, the denser its pop. and the greater its productivity  ecologists can use this to predict the actual or potential distributions of species  to manage conservation of species  ecological niche modeling: a method for predicting the distri. of species from limited info about the range of conditions where indiv. of that species are known to occur 1. map the locations where the species has been recorded in geographic space  known occurrences w/in native distri. 2. graph the physical conditions found in these locations to create and ecological envelope for the species (ecological space)  temperature and precipitation  ecological envelope: the catalogue of ecological conditions of a species  project back onto gepgraphy (native range prediction, and invaded range predi.) 3. map the locations where those conditions occur to predict the species’ distribution in its native region  native range prediction 4. map the locations where those conditions occur in a region to which species has been introduced to predict its potential distribution there  invaded range prediction  accuracy of geographic predictions can be evaluated by dividing the data into a  “training” set: used to construct the ecological envelope  “test” set: used to determine the accuracy of the predicted distribution  knowledge of the entire geographic range allows for accurate ecological niche modeling BIO120H © Li| Page 3011 THE DISPERSION OF INDIVIDUALS REFLECTS HABITAT HETEROGENEITY AND SOCIAL INTERACTIONS  dispersion: the spacing of indiv. w/ respect to one another w/in the geographic range of a pop. (NOTE: dispersal refers to the mvmnts of indiv.)  patterns of dispersion range from clumped to spaced  clumped distri.: indiv. are found in discrete groups  results from: direct interactions b/w indiv.  ex. plants too close to larger neighbours suffer from shading and root competition  evenly sspaceddistri.: each indiv. maintains a min. distance b/w itself and its neighbours  results from: social predisposition to form groups, clustered resources, tendencies of progeny to remain close to their parents  ex. birds find safety in numbers, salamanders aggregate under logs b/c they are attracted to dark, moist places, trees (ex. aspen) form clumps of stems which are all the same indiv. by vegetative reprod.  seed dispersal mechanisms  animals carry seeds over relatively long distances (spreads them evenly through envmt) ex. Baccaurea racemosa  spaced distri.  some have wings (helicopters) ex. Shorea leprosula  clumped distri. (limited dispersal abilities)  pop seeds out of drying capsules (ballistic dispersal) ex. Croton argyratus  clumped distri. (limited dispersal abilities)  on smaller scales, indiv. create regular spacing w/in a clump ex. aspen clones THE SPATIAL STRUCTURE OF POPULATIONS PARALLELS ENVIRONMENTAL VARIATION  suitable envmts vary in quality  some have resources to support large pop, others of similar size have fewer resources or diff. vegetation structure  w/in the geographic range of a pop, the # of indiv. per unit of area (population densdensity varies Variation in Population Density  the narrow range of conditions a species is adapted to support the highest pop. densities  found closer to the centre of a species’ distribution (geographic range)  D decreases towards the periphery of its range  this pattern is irregular since envmtal conditions don’t vary smoothly Ideal Free Distributions  indiv. choose the best quality habitat patches to maximize its access to resources  good patches fill quickly  indiv. settle in highest-quality patches first, then resources become depleted and quality of the patch decreases; poor patches become equally good choices at this point  thus, indic. move from better to poorer patches until each patch has the same value for indiv. fitness, regardless of the intrinsic patch quality  ideal free distribution: the distri. of indiv. across habitat patches of diff. intrinsic ideal free distribution quality such that the realized quality of the patches, in terms of fitness for the indiv. occupying them, is equalized BIO120H © Lis| Page 411  tested the patch-seeking behaviour of the fish by providing food (water fleas) at diff. rates at opposite ends of an aquarium  two diff. patches Manfred Milinski (tendencies  differed in quality (decreased as the # of fish using the patch increased) toward an ideal  fish were free to move b/w patches free distribution)  fish distributed themselves b/w the 2 halves in the ratio stickleback fish predicted for an idea free distribution (5:1)  when the patches were switched, the fish followed research studys  fish used cues (ex. rate
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