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Population Ecology.

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Presentation on theme: "Population Ecology."— Presentation transcript:

1 Population Ecology

2 Population Dynamics and Carrying Capacity
study of how populations change in size, density, and age distribution populations respond to their environment change according to distribution

3 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 population’s increase. Carrying capacity – the upper limit to the population of any particular organism that an ecosystem can support

4 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

5 Biotic Potential and Environmental Resistance
Lack of food or nutrients Lack of water Lack of suitable habitat Adverse weather Predators Disease Parasites Competitors Biotic Potential Reproductive rate Ability to migrate (animals) or disperse (seeds) Ability to invade new habitats Defense mechanisms Ability to cope with adverse conditions


7 Exponential and 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


9 Natural Population Curves

10 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

11 The Role of Predation in Controlling Population Size
Top-down control - lynx preying on hares periodically reduce the hare pop. Bottom-up control - the hare pop. may cause changes in lynx pop.

12 Species Interactions Niche Competition Symbiotic Relationships
Interspecific Intraspecific Symbiotic Relationships Mutualism Parastism Commensalism

13 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

14 Reproductive Patterns and Survival
OBJ 9.10 Reproductive Patterns and Survival r-selected species vs. K-selected species Fig p. 170

15 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.

16 Age Structure Stages PREREPRODUCTIVE AGE
- Not mature enough to reproduce REPRODUCTIVE AGE - Capable of reproducing POSTREPRODUCTIVE AGE - too old to reproduce

17 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

18 Calculating Population Growth
N0 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) and e is the constant (the base of natural logarithms)

19 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.

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