Presentation on theme: "Population Ecology. Population Dynamics and Carrying Capacity Population dynamics -study of how populations change in size, density, and age distribution."— Presentation transcript:
Population Dynamics and Carrying Capacity Population dynamics -study of how populations change in size, density, and age distribution -populations respond to their environment -change according to distribution Population dynamics -study of how populations change in size, density, and age distribution -populations respond to their environment -change according to distribution
Dynamics of Natural Populations Population growth curves Biotic potential - the ability to increase population numbers Environmental resistance - the combination of all the biotic and abiotic factors that limit a populations increase. Carrying capacity – the upper limit to the population of any particular organism that an ecosystem can support
Density Dependence And Critical Number Environmental resistance factors can be density dependent. – If population density increases, environmental resistance becomes more intense and causes in increase in mortality. – If population density decreases, environmental resistance lessens, allowing the population to recover. – Food, Water, Disease, Predation Environmental factors that cause mortality can be density independent – A sudden deep freeze in spring – A fire that may kill all small mammals – Natural Disasters
Biotic Potential – Reproductive rate – Ability to migrate (animals) or disperse (seeds) – Ability to invade new habitats – Defense mechanisms – Ability to cope with adverse conditions Environmental resistance – Lack of food or nutrients – Lack of water – Lack of suitable habitat – Adverse weather – Predators – Disease – Parasites – Competitors Biotic Potential and Environmental Resistance
Exponential and Logistic Growth LOGISTIC GROWTH - Rapid exp. growth followed by steady dec. in pop. Growth w/time until pop. Size levels off EXPONENTIAL GROWTH -Population w/few resource limitations; grows at a fixed rate
Natural Population Curves
STABLE – pop. Size fluctuates above or below its carrying capacity – Stable population size – EX: undisturbed tropical rain forests IRRUPTIVE – pop. Growth occasionally explodes to a high peak then crashes to stable low level – EX: Algae, insects CYCLIC – Fluctuations occur in cycles over a regular time period – EX: Lynx & snowshoe hare IRREGULAR – No recurring pattern in changes of population size
The Role of Predation in Controlling Population Size Top-down control - lynx preying on hares periodically reduce the hare pop. Top-down control - lynx preying on hares periodically reduce the hare pop. Bottom-up control - the hare pop. may cause changes in lynx pop. Bottom-up control - the hare pop. may cause changes in lynx pop.
How do Species Reproduce ASEXUAL REPRODUCTION – all offspring are exact genetic copies of a single parent – Common in single celled species (bacteria) – Each cell divides to produce 2 identical cells SEXUAL REPRODUCTION – Organisms produce offspring by combining sex cells or gametes from both parents – Produces offspring with combination of genetic traits from each parent – Provides greater genetic diversity in offspring DISADVANTAGES – Males do not give birth – Increased chance of genetic errors and defects – Courtship & mating rituals consume time & energy and transmit diseases
Reproductive Patterns and Survival r-selected species vs. K-selected species Fig p. 170 OBJ 9.10
Survivorship Curves Shows the % of members in a pop. Surviving at different ages LATE LOSS -High survivorship to certain age; then high mortality -EX: elephants, rhinos, humans CONSTANT LOSS -Fairly constant death rate at all ages -EX: songbirds EARLY LOSS -Survivorship is low early in life -EX: annual plants, bony fish sp.
Age Structure Stages PREREPRODUCTIVE AGE - Not mature enough to reproduce REPRODUCTIVE AGE - Capable of reproducing POSTREPRODUCTIVE AGE - too old to reproduce
Factors Governing Changes in Population Size Four variables – births, deaths, immigration and emigration Population Change = (births + immigration) – (deaths + emigration) Crude Birth Rate = CBR = (births/population)*1000 Crude Death Rate = CDR = (deaths/population) *1000 Immigration and emigration are calculated the same way Crude Growth Rate = CBR = CDR Population Growth Rate = CGR * 100
Calculating Population Growth N 0 is the starting population N is the population after a certain time, t, has elapsed, r is the rate of natural increase expressed as a percentage (birth rate - death rate) andbirth rate - death rate e is the constant (the base of natural logarithms)
Growth Curves – Two Types J or S Exponential growth results in population explosion Rule of 70 to find the doubling time of a quantity growing at a given annual percentage rate, divide the percentage number into 70 to obtain the approximate number of years required to double. For example, at a 10% annual growth rate, doubling time is 70 / 10 = 7 years. This results in a J curve graph.