IB Biology HL 1-2: C 4.1 Populations and Communities PDF

C 4.1 Populations and Communities C.4.1.1 - C.4.1.8 IB Biology HL 1-2 C. 4.1.1 Populations as interacting groups of organisms of the same species living in an area Population: a group of individual organisms of the same species living and interacting in the same area Species: Inter...

C 4.1 Populations and Communities C.4.1.1 - C.4.1.8 IB Biology HL 1-2 C. 4.1.1 Populations as interacting groups of organisms of the same species living in an area Population: a group of individual organisms of the same species living and interacting in the same area Species: Interbreed to produce fertile offspring C. 4.1.2 Estimation of population size by random sampling Estimated, not counted (good for large populations) Based on evidence → sampling Random sample: every member of a population has an equal chance of being selected for the sample Can use grids or quadrat to estimate Sampling error: difference between the true and estimated value C.4.1.3 Random quadrat sampling to estimate population size for sessile organisms Quadrat: A frame that is a fixed size and used for random sampling Good for counting sessile organisms (non moving) Mark the boundary Generate random numbers (grid, direction & steps) Standard deviation indicates the degree of variability Boundary of population C.4.1.4 Capture-mark-release-recapture and the Lincoln index to estimate population size for motile organisms Motile (moving) organisms are hard to count 1. Capture Assumptions - evaluates 2. Mark (M) reliability 3. Release No migration 4. Recapture (N) No deaths/births 5. Calculate the Lincoln index Marked and unmarked have the same chance of being Population size (Lincoln index) = (M x N)/R captured Marks remain visible R = recapture with marks Marks do not affect survival C.4.1.5 Carrying capacity and competition for limited resources Carrying capacity: maximum population size that an environment can support Specific to each population in each habitat Resources are limited Scarce resources promote competition Examples Plants: water, light, nutrient Animals: water, food, territory, oxygen C.4.1.6 Negative feedback control of population size by density-dependent factors Negative feedback control: populations might rise and fall periodically but are relatively stable over time There are factors that can increase of decrease populations 1. Density independent: same effect no matter the population size Ex. fires 2. Density dependent: have an increasing effect when the population is larger a. Competition b. Predation c. Diseases/parasites C.4.1.6 Negative feedback control of population size by density-dependent factors More breeding More deaths and fewer and fewer deaths births carrying capacity More deaths More breeding and fewer and fewer births deaths C.4.1.7 Population growth curves Sigmoid curve Positive feedback: reproduction causes exponential growth Exponential growth happens when density-dependent factors are not effective Plateau phase or there is movement into a new niche where resources are abundant Exponential (example: Eurasian collared drove) phase C.4.1.8 Modelling of the sigmoid population growth curve Model: a small miniature environment (mesocosm, or habitat with ample resources) Duckweed or yeast (we will attempt to do it with algae!) Start with small number of organisms and abundant resources Can investigate carrying capacity or factors that affect growth What are the strengths and limitations to using models?