Population Dynamics Student Notes PDF

 Quantitative measurements of populations are like snapshots of moments in time  Ecologists often rely on a number of measurements over a long period of time to make inferences about population growth  Both the distribution and growth of a population can be significant when studying pop...

 Quantitative measurements of populations are like snapshots of moments in time  Ecologists often rely on a number of measurements over a long period of time to make inferences about population growth  Both the distribution and growth of a population can be significant when studying populations and communities  habitat and lifestyle can play a role in how populations are distributed  population distributions can follow one of three general patterns: 1  Clumped - most common type found in nature - found in environments that is characterized by low resources needed to survive and as they become rare, clumping of populations around resources occur - Used by organisms that have cooperative behaviors (hunter or predator evasion) Examples: Random - unpredictable spacing, is the least common form of distribution in nature - occurs when the environment is homogenous - no strong social interactions Examples: 2 Uniform - Less common than clumped distribution. - the distance between neighboring individuals is maximized due to: a) competition for a resource b) direct social interactions between individuals within the population, such as territoriality. Examples:  Density  D= N/A D = N / V where:  D = density  N = # of organisms  A = area  V = volume (aquatic habitats) 3  4 factors determine population size: 1. Natality – number of births = b 2. Mortality – number of deaths = d 3. Immigration – number of organisms moving into an area = i 4. Emigration – number of organisms moving out of an area = e Open population = has all four factors; closed has only #1 and #2 influencing the population  population change: ∆N = (b + i) – (d+ e) Other calculations:  per capita growth rate: (often given as a %) cgr = ∆N/ N, where N = Initial number of organisms  Growth rate: gr = ∆N/ ∆t where t = time 4 5 6  Biotic Potential: is the maximum growth rate under ideal conditions. It is usually held in check by environmental resistance. It depends on a number of factors: 1. Offspring – the maximum number of offspring per birth 2. Capacity for Survival – the chances of offspring reaching reproductive age 3. Procreation – the number of times per year an organism reproduces 4. Maturity – the age at which reproduction begins  Generally, growth in small populations begins slowly and then the rate of growth increases  However, the growth must eventually slow because there is a maximum number of organisms that an ecosystem can support 7 1. 2. 3. 4.  Many populations exhibit an S-shaped (sigmoidal) growth curve  This is also known as a logistic growth pattern  The population number increases until it reaches the carrying capacity of the ecosystem  At this point, the population fluctuates near the carrying capacity 8  J – shaped curves are representative of quick growth and then may show a sharp decline in the population  this occurs when a population quickly outgrows the carrying capacity of an ecosystem  as a result, there is a crash in the population, which may be followed by a new growth phase  these J-curves are most often associated with organisms that can reproduce very quickly (insects, bacteria, etc.) B30 http://www.emc.maricopa.edu 9 Limiting Factors (environmental resistance) any limiting factors that are not affected by population density are density independent - factors that are dependent on the population density are density dependent – often problems involving density-dependent factors are alleviated when a population density returns to lower levels  K-selected populations:  Characteristics:  late maturation  fewer, larger young see text p. 756  longer life spans  more parental care  intense competition for resources 10 r-selected populations:  Characteristics: early maturation numerous, smaller young see text p. 756 shorter life spans less parental care little competition for resources Info needed for text p. 756 #6 11