Population Biology Concepts 1. Population Ecology • The study of a group of individual organisms of the same species living in a particular area in how they interact amongst themselves, with other species and with their non‐living environment. 2. Carrying Capacity • The maximum population of a species that a given area can sustain over a period of time. • There are four different types of capacity curves in nature: a. Stable b. Irruptive c. Irregular •
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d. Cyclic
The ‘intrinsic rate of increase’ is the rate a population would grow at with unlimited resources. Population dynamics are affected by: a. size – the number of individuals b. density – the number of individuals in a specific place c. dispersion – the spatial pattern
d.
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age distribution – proportion of individuals at each age in a population Biotic potential is a population’s capacity for growth. •
If carrying capacity is exceeded: a. a population did not make a smooth transition from exponential growth (‘J’ curve)
to logistic growth (‘S’ curve)
b. the population overshot the carrying capacity because of a ‘reproductive time lag’ in which the birth rate and death rate have not yet adjusted to the size of the population c. the population will experience a ‘dieback’ or ‘crash’ to even out the population • No population can grow indefinitely (‘J’ curve), there is always a limit (‘S’ curve). • Carrying capacity is affected by: a. competition within a species or between species b. immigration and emigration c. catastrophes (natural or caused by humans) d. seasonal fluctuations in things necessary for survival 3. Reproductive Strategies • In order to ensure the most/healthiest off‐spring some species (r) do one or more of the following: a. reproduce early in life b. have short amounts of time between successive generations c. reproduce multiple times d.
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have many off‐spring each time they produce
Other species (k) tend to: a. put little energy into reproduction b. reproduce late in life c. have fewer offspring and longer generation times d. put a lot of energy into protecting and caring for their offspring until they reach reproductive age The offspring of K‐species often: a. reproduce inside their mothers b. are fairly big c. mature more slowly than r‐species d. are cared for by their parents until they reach their reproductive age
• Asexual reproduction is when a single organism creates exact copies of itself. • Sexual reproduction is two organisms combine sex cells to produce offspring that have traits from both parents. • Risks and costs of sexual reproduction include: a. chances of genetic error as chromosomes split and recombine b. females must produce more young each generation than asexually reproducing organisms do c. mating is time‐consuming, females run the risk of being injured and diseases can be transmitted 4. Survivorship • Survivorship curves show the number of survivors for a particular species compared with other species. a. Late loss curve – applies mainly to K‐selected species that care for their young until about reproductive age, reducing juvenile mortality. b.
c.
Early loss curve – usually applies to r‐selected species. They often die young, but after a certain age there are high survivorship rates. Constant loss curve – Mortality rates increase with age.
*All pictures and facts come from Miller’s Thirteenth Edition of Living in the Environment.