OPTION C.5 POPULATION ECOLOGY

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1 OPTION C.5 POPULATION ECOLOGY

2 INTRO IB BIO C.5 2 Recall that populations are made up of members of the same species that inhabit the same area. The potential size and growth of a population (including microbes) is determined by several factors.

3 C.5 A Population Growth

4 IB BIO C.5 4 Overall, population size is affected by four primary factors: Applications A3: Discussion of the effect of natality, mortality, immigration and emigration on population size. Natality new members due to reproduction Immigration Natality Population Size Mortality loss of members due to death Emigration Nataliy/ Mortality Immigration/ Emigration Immigration arrival of new members from other populations Mortality Emigration members migrating away from the populations

5 IB BIO C.5 5 U2: The exponential growth pattern occurs in an ideal, unlimited environment. In ideal environments with unlimited space, populations are able to grow exponentially without limit (natality > mortality). This can be represented with a J-shaped curve for population size. This pattern results from: Food/water availability Unlimited space Lack of competition J-shaped Curve Lack of predation Lack of disease

6 IB BIO C.5 6 U2: The exponential growth pattern occurs in an ideal, unlimited environment. In the real world, exponential growth is observed when a population inhabits a new area. For example, the European rabbit population exploded after being introduced to Australia. J-shaped Curve

7 IB BIO C.5 7 U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration In reality, though, exponential growth cannot continue indefinitely. As competition for resources and other external factors affect the population, growth will slow and eventually level off.

8 IB BIO C.5 8 U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration As populations grow, they are affected by density-dependent factors. These act on populations as their density increases and slow growth. Examples include: Competition for resources Increased predation Disease Accumulation of metabolic waste products

9 IB BIO C.5 9 U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration Changes in population growth rate are shown in the sigmoid curve (s curve) which is shown below. The curve is divided into distinct phases that result from complex interactions. Sigmoid Curve

10 IB BIO C.5 10 S-Curve: Exponential Phase U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration Initially, resources are abundant so natality is greater than mortality. This results in exponential population growth. Exponential Sigmoid Curve

11 IB BIO C.5 11 S-Curve: Transition Phase U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration As population size increases, density-dependent factors begin to affect growth rate. Natality decreases while mortality increases. Exponential Sigmoid Curve Transition

12 IB BIO C.5 12 S-Curve: Transition Phase U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration As a result, the rate of growth slows which is represented by a decreasing slope in the curve. Exponential Sigmoid Curve Transition

13 IB BIO C.5 13 S-Curve: Plateau Phase U4: The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration The plateau phase occurs when populations saturate resources. Natality/mortality and immigration/emigration are balanced. Exponential Plateau Sigmoid Curve Transition

14 IB BIO C.5 14 Carrying capacity (K) is the maximum size of a population that an U3: Population growth slows as a population reaches the carrying capacity of the environment. environment can support. As populations reach the capacity, the rate of growth slows until a plateau is established. K Exponential Plateau Carrying Capacity Transition

15 IB BIO C.5 15 It is important to note that populations will fluctuate around the U3: Population growth slows as a population reaches the carrying capacity of the environment. carrying capacity. When size is above or below the K value, natality/mortality rates change accordingly to maintain balance. Carrying Capacity

16 IB BIO C.5 16 Population growth curves can be modelled with simple species like Skills S1: Modelling the growth curve using a simple organism such as yeast or species of Lemna. Lemna minor, floating aquatic plants. Factors such as surface area and light can be altered to study growth rates and carrying capacity.

17 IB BIO C.5 17 U5: Limiting factors can be top down or bottom up. A population s carrying capacity is determined by limiting factors. These can be classified as: Top down Factors resulting from species in higher trophic levels (predation) or keystone species. Top Down Bottom Up Bottom up Factors related to the availability of resources (food, water, space, etc.)

18 IB BIO C.5 18 U5: Limiting factors can be top down or bottom up. For example, Snowshoe hares are prey to the Canada lynx. So, the larger the population of lynxes, the more the population size of hares will be regulated by predation. This factor is top down. Hare-Lynx Data Hare (orange) Lynx (blue) Top Down Bottom Up

19 IB BIO C.5 19 U5: Limiting factors can be top down or bottom up. Bacteria colonizing a petri dish are able to grow uncontrolled until space and nutrients in the agar are no longer available. Since these are necessary resources, they are bottom up limiting factors. Top Down Bottom Up

20 IB BIO C.5 20 Applications A5: Bottom-up control of algal blooms by shortage of nutrients and top-down control by herbivory. Both types of limiting factors can be seen in the control of algal blooms. These are rapid increases of algae populations in freshwater systems that disrupt communities by blocking sunlight. Top Down Bottom Up Algal Bloom

21 IB BIO C.5 21 Applications A5: Bottom-up control of algal blooms by shortage of nutrients and top-down control by herbivory. Algal Bloom: Top Down Control Herbivorous fish feed on free-living algae and control the population size. However, human fishing practices can reduce the fish population, resulting in algae population size increasing. Top Down Bottom Up Algal Bloom

22 IB BIO C.5 22 Algal Bloom: Bottom Up Control Applications A5: Bottom-up control of algal blooms by shortage of nutrients and top-down control by herbivory. Decreases in photosynthetic organisms due to blocking sunlight decreases the nutrients available to free-living algae. These nutrients are needed to synthesize proteins and chlorophyll pigment. Top Down Bottom Up Algal Bloom

23 IB BIO C.5 23 Applications A4: Analysis of the effect of population size, age and reproduction status on sustainable fishing practices. Fish are an important food resource worldwide. As a result, it is in our best interest to implement sustainable fishing practices so that populations do not become extinct.

24 IB BIO C.5 24 According to the sigmoid curve, the point between the exponential Applications A4: Analysis of the effect of population size, age and reproduction status on sustainable fishing practices. and transition phase is best for maximizing yield. Populations are growing at the maximum rate and so will repopulate quickly. Exponential Plateau Transition

25 IB BIO C.5 25 Sustainable fishing practices aim to maximize the amount of fish Applications A4: Analysis of the effect of population size, age and reproduction status on sustainable fishing practices. obtained while not permanently damaging populations. Several international agreements have been established for open waters.

26 IB BIO C.5 26 Sustainable fishing practices Applications A4: Analysis of the effect of population size, age and reproduction status on sustainable fishing practices. include: Regulations on catching younger fish as their reproductive capabilities allow for repopulation Agreements to not fish endangered species Established fishing seasons so that populations can breed and grow during off-seasons. Banning certain methods. For example, dredging causes structural damage to habitats.

27 REVIEW IB BIO C Outline factors describing population size. 2. Draw and label a sigmoid population curve. 3. Outline each phase of a sigmoid curve. 4. Describe carrying capacity and factors that affect it. 5. Define limiting factors. 6. Differentiate between top down and bottom up limiting factors using examples. 7. Outline two potential practices of sustainable fishing