Population and Community Dynamics Chapters 19 and 20

Populations Population size: number of individual organisms present at any one time May increase, decrease, undergo cyclical change or remain stable over time

Population Density Number of individuals in a population per unit area High density makes it easier for organisms to mate and clump together, but can also increase competition and instances of infection diseases

Population Distributions Spatial arrangement of organisms in an area Random Uniform Clumped

Population Distribution Random Resources are plentiful and other organisms do not strongly influence the population Uniform Occur when individuals hold territory or compete for space; ex: desert plants Clumped Most common; arrangement according to availability of resources; ex: humans

Life History Patterns Type I: Type II: Type III: Survival rates are high when organisms are young and decrease sharply when they are old Type II: Survival rates are equivalent regardless of an organism’s age Type III: Most mortality takes place at young ages and survival rates are greater at older ages

Life History Patterns

Population Growth Exponential Growth Rate of increase goes up as the total number of females goes up Populations undergo exponential growth unless they meet constraints

Habitats Limiting Factors Physical, chemical, biological attributes of the environment that restrain population growth Any factor whose shortage or absence restricts species success Density Independent Density Dependent

Carrying Capacity Carrying Capacity Maximum population size of a species the environment can continuously support and sustain The closer the population is to the carrying capacity, the greater the environmental resistance

Carrying Capacity

Logistic Curve is just a model  

Kinds of Organism Interactions Predation - One animal kills/eats another. Predator benefits from food. Prey adaptation is manifested in a higher reproduction rate.

Prey Defenses Prey defenses Mechanisms to prevent being eaten Spines Tough epidermis (skin) Poisonous Chemicals Camouflage Bright Coloration Flocking Behavior

Lynx and Snowshoe Hare

Competition Competition - Two organisms strive to obtain the same limited resource, and both are harmed to some extent. Intraspecific - Members of same species competing for resources. Interspecific - Members of different species competing for resources. The more similar the competing species, the more intense the competition.

Mimicry Mimicry One species resembles another species Mimicked species possesses an overt antipredator defense 2 types of Mimicry Müllerian Batesian

Mimicry Müllerian Mimicry - Mimic shares same protective defense

Mimicry Batesian Mimicry - Mimic lacks defense of the organism it resembles

Symbiotic Relationships Symbiosis - Close, physical relationship between two different species. At least one species derives benefit from the interaction. Parasitism - One organism (parasite) lives in or on another organism (host), from which it derives nourishment.

Ectoparasites - Live on host’s surface. Fleas Endoparasites - Live inside host. Tapeworms

Symbiotic Relationships Commensalism - One organism benefits while the other is not affected. Remoras and Sharks Mutualism - Both species benefit. Obligatory in many cases as neither can exist without the other. Coral and Zooxanthellae

Cleaning Symbiosis