Chapter 11 Intraspecific Population Regulation I Population growth

Chapter 11 Intraspecific Population Regulation

I. Population growth curves • No population grows indefinitely – Will confront the limits of environment – Most do not grow exponentially • Interactions tend to regulate population’s size

II. Regulation by growth mechanisms 1. Density-dependence = regulation by mechanisms controlled by size of population 2. Density-independence = effects of influence do not change with population density

1. Density-dependent • Effect increases as population size increases • No influence at low density • Larger population / more individuals affected • Largely through competition for resources

2. Density-independent • Effects do not change with population density • Proportion of individuals affected – same at any density • Can have significant impact on populations • Can mask or eliminate densitydependent regulation

III. Competition • Among same species individuals for resources • One aspect of population regulation • 2 kinds of competition – Scramble competition—no one receives enough of the resource – Contest competition—some claim enough and deny others a share

• Limited resource will cause species to exhibit only one type of competition • Scramble competition—produces chaotic oscillations in populations – Wastes resources—limits average density to below carrying capacity of habitat • Contest competition—causes a fraction to suffer (unsuccessful individuals) – Eliminates waste of resources – Permits maintenance of high density

• As populations increase toward insufficient resources, scrambling competition reduces food intake. • this slows growth and limits reproduction • seen in overstocking of fish • vertebrates fecundity affected • Biomass—a function of accumulated living tissue • can be few large or many smaller individuals

IV. Aggression • High density causes stress • Aggressive contacts increases • Stress triggers hyperactivation endocrine glands – Suppresses growth, reproduction and immune system

V. Coping with stress • Pheromones encourage or inhibit reproduction • Seeking new vacant habitat—dispersal – Success rate low – Few arrive at suitable habitat and flourish • Dispersal before resource depletion is important with low density

VI. Dispersal • Individuals dispersed are normally in good condition, either sex, any age—good chance of survival • Relocation habitats have increased resources + breeding sites, decreased competition • Distance relative to availability of habitat • Requires a source and sink

VII. Social issues of populations Social behavior limits populations: 1. Surplus animals, not breeding, or attempting and failing 2. Prevented from breeding 3. Removal of dominant animals results in breeding of surplus animals 4. Breeding animals not using all space or food

Social organization • Common in populations • Based on aggressiveness, intolerance and dominance of one over another • 2 opposing forces at work – Mutual attraction – Negative reaction against crowding and need for personal space

Simple social organization • • Alpha individual—dominant over all Beta—dominant over all except alpha Omega—subordinate to all Rankings established by fighting, bluffing, threatening • Ranking maintained by habitual subordination and punishment • Important for populations—stabilizes intraspecific competition – Resolves disputes with minimal energy

IX. Movement and distribution • The space occupied during a year = home range – May differ with sex – Not defended • Range defended = territory – Varies with availability of food • Size of territory – – Carnivores > herbivores/omnivores Dominant > subordinate Males > females Adults > subadults

Territoriality • Animal defends exclusive area no shared with rivals • Occurs in regular patterns of distribution • Costly in energy and time – May interfere with breeding, feeding and rearing of young • Quality territory = dominant male • Floating reserve—evicted individuals

X. Territory vs home ranges • Indicates the carrying capacity • Management becomes ecological/economical problem • Plants can be territorial – Shading and competition for nutrients – Release of organic toxins

XI. Review • Density dependent influences population growth and fecundity • Density independent factors may be more important – May eliminate density dependent factors – May go beyond a limit of tolerance