Ecology part Two Populations!
Population Ecology • Characteristics of a population • Population Density – The number of organisms per given area • Supplies info….chances of reproduction, feeding, nesting site availability • Growth Rate – The change in size of a population over time • Birth rate, death rate • Immigration and emigration • Geographic Distribution – The area on earth or “homerange” in which we find a population.
Biotic PotentialBiotic Potential: maximum reproductive rate of an organismGiven unlimited resources and no limiting factors, many species can produce enormous populations very quickly (e.g. houseflies). Is Biotic Potential ever reached???
Population Growth Curve (K) Competitive ability is crucial when a Population is at “K” Logistic Growth High Rep. Rate Exponential Growth Env. Resistance - Factors that reduce population growth Plenty of resources
Important Terms • Biotic Potential – see previous slide • Limiting factors keep this from occurring in nature. • Carrying Capacity (K) – The number of individual organisms an environment can support! • The environment tends to reach a point where it can’t support any more! • Usually follows exponential growth! • Population Cycle – The population growth and decline of individual species over time • Often measurable and consistent! • Ex: Ruffed Grouse – 10yr cycle
Cycle within a cycle: The ruffed grouse population shows peaks and valleys about every 10 years, with "super peaks" every 20 years. But a super peak only lasts for one year, while the lower peaks can last two to three years
Factors that regulate population growth Biotic and Abiotic Limiting Factors • Density independent – When the influence of a limiting factor is NOT a result of population density. (tend to be abiotic) • Extreme cold during the wrong time of year • High heat, drought, excessive rain, flood, volcanic eruption, forest fire, severe storm • Density Dependent – When the influence of a limiting factor changes with population density (size) • Predation, Parasitism and disease, Competition • Usually biotic
Answer the following questions • What organisms were studied? • How was the data collected? • What type of population “event” does the graph show? • Why does the lynx population seem to increase after the hare population increases? • Why is the hare population always larger than the lynx population?
In 1911, 25 reindeer ‑ 4 males and 21 females ‑ were introduced onto Saint Paul Island, one of the Pribilof Islands in the Bering Sea near Alaska. Saint Paul Island is approximately 106 square kilometers in size, and is more than 320 kilometres from the mainland. On Saint Paul Island there were no predators of the reindeer, and no hunting of the reindeer was allowed. The graph below indicates what happened to the reindeer population on the island between 1911 and 1950.
Answer the following questions. • Could immigration or emigration have played a major role in determining the size of the reindeer population? Explain • What could account for the tremendous increase in population between 1930 – 1938 as compared to the first few years? • What might have caused the decline in reindeer population between 1938 – 1950? • What difference might hunting or introducing predators have made? ***Heron population in England and Wales*** (additional study)
Competition – A Density Dependent factor • Interspecific Competition – Competition between different species • MacArthurs Warblers – Solved through Niche Partitioning • Connell – Barnacles (competition for space) • 1961 Research Paper • Rocky Intertidal #1 • Rocky Intertidal #2 • Rocky Intertidal #3
Competition – A Density Dependent factor Intraspecific Competition – Competition between members of the same species • Ways to reduce intraspecific competition • Social hierarchy - wolves • Role separation – ants, bees • Territoriality • Aggression – yes…it happens in nature!
Summary! • Given optimal conditions, populations of many organisms can grow exponentially. • Some populations will grow exponentially until they overshoot the carrying capacity of the environment. • Mortality rates rise as resources become limited and the population may crash. • Most important components of population dynamics are fertility, life span, longevity, mortality, immigration, and emigration. • Factors that regulate population dynamics can be caused by biotic or abiotic forces, and can act on the population in either a density-dependent or density-independent fashion. • The most important abiotic factors are usually climate and weather. • The most important biological factors are usually competition (both interspecific and intraspecific), predation, and disease. • Extreme crowding can result in stress-related diseases that can lead to a variety of deleterious health effects.