Ch 5 Populations and Communities 5.1 Populations I. population group of same species Exponential Model - adding a large number of individuals with each generation ex: humans in last 200 yrs and bacteria limiting factor - restrains growth - space, any resource Logistic Model - growth assumes a capacity - carrying capacity - number of individuals the environment can support over a long period of time ex: most natural things A. 2 kinds of limiting factors 1. density-independent factors a. does not depend on pop. size b. ex: weather, floods, and fires 2. density-dependent factors a. triggered by increasing population size b. resource limitations like food shortage or lack of nesting sites IV. Population Regulation Population Regulation, cont B. All populations fluctuate (go up and down) in size V. Human population growth Exponential growth Why? Population Dispersion Clumped Dispersion Is the tendency for populations to be found in tight clusters, dispersed across a large landscape. In between these population hubs, very few to no individuals are usually found. This sort of a dispersion can be caused by a number of factors. Some species cluster together for protection, while others group around natural resources necessary to their survival. Uniform Dispersion Is the tendency for populations to be found evenly distributed about their habitat. This is generally caused by a species ability to survive anywhere in their habitat - they use the resources found immediately around them, and spread out as to use all of the available resources. Random Dispersion Is the tendency for populations to be found randomly about their habitat. In immobile species, this is usually caused by their ability to live anywhere in a given habitat, except, they are limited to growing wherever they are first set root (which is usually caused randomly, from spores drifting in the wind to seeds falling and tumbling on the ground). In motile populations, individuals are able to move about their habitat, so that at any given instance, they can be found anywhere about their environment. 5.2 Interactions in communities I Type of interactions A.Coevolution the evolution of 2 or more species that is due to mutual influence -If rabbits get faster, so do fox. -B. Parasitism one harmed one benefits -C. mutualism both benefit -D. commensalism one benefits other is unharmed Animal Interactions Summary of: Predator/Prey (Lion vs. Zebra)Lion vs. Zebra Mutualism (Bird & Water Buffalo)Bird & Water Buffalo Commensalism (Nurse Shark & Remora)Nurse Shark & Remora Parasitism (Cricket & Worm) (Complex Life Cycle) (ParasitoidCordyceps)Cricket & WormComplex Life CycleParasitoidCordyceps 5.3 Shaping communites II. Keystone species species critical to an ecosystem many others depend on it I. Niche role organism plays in community Predator/ prey /etc, comfort zone