Population Distribution and Abundance Chapter 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Introduction Ecologists usually define a _____________ as a group of individuals of a single species inhabiting a specific area. Characterized by the number of individuals and their ____________. Additional characteristics of a population …

Distribution Limits _________________________limits geographic distribution of a species. Organisms can only compensate so much for environmental variation.

Niches __________: Summarizes environmental factors that influence growth, survival, and reproduction of a species. Grinnell’s definition focused on the effects of … Elton’s definition included …

Niches Hutchinson defined niche as: n-dimensional hyper-volume n equates to… _______________________- hypervolume _______________________ -includes interactions such as competition that may restrict environments where a species may live.

Kangaroo Distributions and Climate

Kangaroo Distributions and Climate Limited distributions may not be directly determined by climate. Climate often influences species distributions via:

Tiger Beetle of Cold Climates

Distributions of Plants Along a Moisture-Temperature Gradient Encelia species distributions correspond to variations in temperature and precipitation.

Distributions of Barnacles Along an Intertidal Exposure Gradient Organisms living in an intertidal zone have evolved to different degrees of resistance to drying. Barnacles show distinctive patterns of zonation within intertidal zone. Connell found Chthamalus stellatus restricted to upper levels while Balanus balanoides is limited to middle and lower levels.

Distributions of Barnacles Along an Intertidal Gradient

Distributions of Barnacles Along an Intertidal Gradient Balanus appears to be more vulnerable to … Chthamalus adults appear to be excluded from lower areas by …

Distribution of Individuals on Small Scales __________: Equal chance of being anywhere. ________________of resources. __________: Uniformly spaced. __________: Unequal chance of being anywhere. Patchy …

Distribution of Individuals on Small Scales

Distribution of Tropical Bee Colonies Hubbell and Johnson predicted aggressive bee colonies would show regular distributions while non-aggressive species would show random or clumped distributions. As predicted, four species with regular distributions were highly aggressive. Fifth was non-aggressive and randomly distributed. Prospective nest sites marked with pheromones.

Distributions of Desert Shrubs Traditional theory suggests desert shrubs are… Phillips and MacMahon found distribution of desert shrubs changes from … Young shrubs clumped for (3) reasons:

Distributions of Desert Shrubs Phillips and MacMahon proposed as plants grow, some individuals in clumps die, reducing clumping. Eventually creates … Brisson and Reynolds found competitive interactions with neighboring shrubs appear to influence distribution of creosote roots, Larrea tridentata.

Google Earth…

Distributions of Individuals on Large Scales Bird Populations Across North America Root found at continental scale, bird populations showed clumped distributions in Christmas Bird Counts. Clumped patterns occur in species with widespread distributions. Brown found a relatively small proportion of study sites yielded most of records for each bird species in Breeding Bird Survey.

Plant Distributions Along Moisture Gradients Whittaker examined distributions of woody plants along moisture gradients in several North American mountain ranges. Documented moisture gradient from moist canyon bottoms up to the dry southwest-facing slopes. Tree species showed a highly clumped distribution along moisture gradients, with densities decreasing substantially toward the edges of their distribution.

Plant Distributions Along Moisture Gradients

Organism Size and Population Density

Organism Size and Population Density In general, population density declines with increasing organism size. Damuth found the population density of herbivorous mammals decreased with increased body size. Peters and Wassenberg found aquatic invertebrates tend to have higher population densities than terrestrial invertebrates of similar size. WHY?!? Mammals tend to have higher population densities than birds of similar size.

Plant Size and Population Density Plant population density decreases with increasing plant size. Underlying details are very different. Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities.

Commonness and Rarity Rabinowitz devised commonness classification based on (3) factors: Populations that are least threatened by extinction, have extensive geographic ranges, broad habitat tolerances, and some large local populations. All seven other combinations create some kind of rarity.

Rarity Rarity I Rarity II Peregrine Falcon Passenger Pigeon http://falconrytoday.net/news/wp-content/uploads/2009/08/Peregrine-Falcon0014.jpg http://www.saroffillustration.com/portfolio/page/ns4_pigeon.jpg

Rarity Rarity III California Condor http://www.dfg.ca.gov/wildlife/hunting/condor/images/condor119.jpg