Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Population Biology Population Growth 1. 2. 3. 4. 5. 6. Review: What is a population? What is population growth? How is population growth determined? When does it happen? Why is it important? How fast do populations grow…? Biotic Potential • The biotic potential of a population is its potential to grow (in numbers) if all offspring survive and reproduce at max capacity • Biotic potential is not reached in nature – why? • Offspring die • Not all reproduce • Limiting factors Dynamics of Growth • More births than deaths = Growth • More deaths than births = Decrease • Deaths = Births: No population growth Dynamics of Growth • Exponential Growth growth at a constant rate of increase per unit time. J Curve - Exponential Growth • Nearly all populations will grow exponentially under ideal conditions • This type of curve shows indefinite (unlimited) growth Exponential Growth • As a population gets larger, it also grows faster • Example: – Bacteria (per 24 hours): 2 – 4 – 8 – Million (25 days later) • This type of growth occurs when: 1. Species moves into a new habitat 2. A new food supply is made available Another Type of Growth: S Curve • Most populations do not grow exponentially for long • Exponential growth stops when a population encounters limiting factor(s) such as availability of food and physical space S Curve (Logistic growth) • When limiting factors are encountered, growth stops increasing, and a “leveling-off” occurs – a flattening out of the graph/curve • This upper limit is called the carrying capacity: the # of individuals the environment can support –Represented by the letter “K” –Population stabilizes Environmental Limits To Population Growth • Limiting Factors: biotic or abiotic factors that determine whether an organism can live in a particular environment; controls growth of population 1. Density Dependant: space (including stress from overcrowding, parasitism &disease, competition, food, predation, herbivory 2. Density Independent (affect all populations in similar ways): temperature, storms, floods, droughts, other disturbances Organism Interactions Limit Population Size • Predation/herbivory – Keeps prey and plant population down; eventually predator population down (fluctuates) • Competition for resources – Demand vs. supply • Crowding and stress – Organisms can exhibit aggression, decreased resistance to disease, decreased fertility Summary • Two opposing forces affect population size: biotic potential and environmental resistance • A graph of typical population growth is an S-curve, with K as the upper limit • A number of environmental factors (density de- and inde- pendant) impose limits on population growth • Predictions of future growth can be made by graphing the age make-up of a population in an age-structure graph