## Population Growth Curves [block_0] 1. Populations don’t grow indefinitely. 2. Over time, they follow a **sigmoid growth curve**, which consists of three distinct phases: rapid growth, slowed growth, and stabilization. 3. This curve explains how populations interact with their environment and the **limits imposed by resources, competition, predators, and diseases**. [{"_key":"block_7","_type":"block","asset":null,"children":[{"_key":"2764cd92b476","_type":"span","markDefs":[],"marks":[],"text":"Recall that a "},{"_key":"df52c6ef5ed7","_type":"span","markDefs":[],"marks":["strong"],"text":"population "},{"_key":"8a6a6d0e8ed6","_type":"span","markDefs":[],"marks":[],"text":"is a group of organisms of the same species living in a specific area."}],"markDefs":[],"style":"normal"}] ## Phases of the Sigmoid Growth Curve [block_8] ### 1. Exponential Growth Phase: [68a7af55b5e6] Population grows **rapidly** due to: 1. Abundant **resources** (e.g., food, space). 2. Few limiting factors like **predators or diseases**. [{"_key":"667cda051c68","_type":"block","asset":null,"children":[{"_key":"9aed9f97f72c","_type":"span","marks":[],"text":"Bacteria in a nutrient-rich petri dish double every few hours during this phase"}],"markDefs":[],"style":"normal"}] [{"_key":"block_21","_type":"block","asset":null,"children":[{"_key":"0cd2283a0c4c","_type":"span","markDefs":[],"marks":[],"text":"Think of a population of rabbits introduced to a new area with plenty of food and no predators. "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"70bcb8808f01","_type":"block","asset":null,"children":[{"_key":"1ffba5db13bd","_type":"span","markDefs":[],"marks":[],"text":"The population will grow quickly as each pair of rabbits produces offspring."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ### 2. Transitional Phase [block_22] Growth slows as **resources become limited**, leading to: 1. **Increased competition** for food, space, and water. 2. **Higher mortality rates** as some individuals cannot survive or reproduce. [{"_key":"block_29","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZviYu","_type":"span","markDefs":[],"marks":[],"text":"This phase marks the beginning of environmental resistance, where factors like competition and predation start to limit growth."}],"markDefs":[],"style":"normal"}] ### 3. Plateau Phase [block_30] Population size **stabilizes** near the **carrying capacity** because: 1. **Birth and death rates** are roughly equal. 2. Resources are insufficient to support further growth. [{"_key":"block_37","_type":"block","asset":null,"children":[{"_key":"5c0f2904f0e4","_type":"span","markDefs":[],"marks":[],"text":"Recall that"},{"_key":"b4720a47e0de","_type":"span","markDefs":[],"marks":["strong"],"text":" carrying capacity "},{"_key":"cd395f81020d","_type":"span","markDefs":[],"marks":[],"text":"refers to the maximum population size that an environment can sustainably support."}],"markDefs":[],"style":"normal"}] [{"_key":"block_40","_type":"block","asset":null,"children":[{"_key":"b51a0f96541a","_type":"span","markDefs":[],"marks":[],"text":"A forest can only support a certain number of deer based on the availability of food and space. "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"4577014b38f1","_type":"block","asset":null,"children":[{"_key":"ffdc611c357d","_type":"span","markDefs":[],"marks":[],"text":"Once this limit is reached, the population stabilizes."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## Factors Affecting Population Growth Curves [block_35] ### 1. Predation [27bc6f98dad4] 1. **Impact:** Predators control prey populations by hunting them. 2. **Effect on Curve:** The curve fluctuates as prey population declines, followed by predator decline, then recovery. ![](https://cdn.sanity.io/images/w7j7fz60/production/7c923c43c57d8b82d274c92b4f0c604f13334305-800x401.jpg) [{"_key":"7b250b668208","_type":"block","asset":null,"children":[{"_key":"684d5469e3b4","_type":"span","marks":[],"text":"In predator-prey cycles, an increase in foxes leads to fewer rabbits, which in turn reduces fox numbers."}],"markDefs":[],"style":"normal"}] ### 2. Competition [block_38] 1. **Impact:** Individuals compete for limited resources like food, water, and space. 2. **Effect on Curve:** Growth slows earlier, reducing the **carrying capacity**. ![](https://cdn.sanity.io/images/w7j7fz60/production/0fb1e4ddc819e40ae2ef7167dee93f364917fc8f-736x526.png) ### 3. Disease [block_41] 1. **Impact:** High population density makes it easier for diseases to spread, reducing population size. 2. **Effect on Curve:** Rapid decline during outbreaks, followed by stabilization as the population recovers. ![](https://cdn.sanity.io/images/w7j7fz60/production/aa24f7105c2ee3527588fa2a7bbcbd9d65b24e77-688x464.png) [{"_key":"c01342819650","_type":"block","asset":null,"children":[{"_key":"612672588d11","_type":"span","marks":[],"text":"Disease outbreaks in crowded rat populations can cause sudden declines."}],"markDefs":[],"style":"normal"}] ### Why Exponential Growth Occurs in the Initial Phase [f29f78785378] Exponential growth happens when: 1. **Resources** are **plentiful**. 2. There are **few** **limiting factors** like predators or diseases. 3. The population is **small**, allowing rapid reproduction. [{"_key":"block_49","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZvibI","_type":"span","markDefs":[],"marks":[],"text":"When yeast is added to a sugar-rich environment, it reproduces rapidly until the sugar is depleted or waste products accumulate."}],"markDefs":[],"style":"normal"}] [{"_key":"block_58","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZvibt","_type":"span","markDefs":[],"marks":[],"text":"Remember that the sigmoid curve is an idealized model. Real populations may not follow it perfectly due to factors like sudden environmental changes."}],"markDefs":[],"style":"normal"}] ## Testing Population Growth Against Models [block_59] 1. **Scientists use population growth graphs to:** 1. **Compare **real populations to theoretical models. 2. **Identify **how factors like predation or resource scarcity impact growth. 2. **Graph Setup:** 1. **Logarithmic scale:** Population size on the vertical axis. 2. **Linear scale:** Time on the horizontal axis. [{"_key":"block_66","_type":"block","asset":null,"children":[{"_key":"dc547daa4dd7","_type":"span","markDefs":[],"marks":[],"text":"Imagine tracking the growth of a bacterial population in a lab. "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"b572e33d0998","_type":"block","asset":null,"children":[{"_key":"33bed07bdfac","_type":"span","markDefs":[],"marks":[],"text":"By plotting the data on a graph, you can see how closely it follows the exponential growth model."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"block_74","_type":"block","asset":null,"children":[{"_key":"f09874369ab1","_type":"span","markDefs":[],"marks":[],"text":"How do population growth models help us make decisions about resource management and conservation? "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"d28cbea7f13f","_type":"block","asset":null,"children":[{"_key":"771a042d6af0","_type":"span","markDefs":[],"marks":[],"text":"What are the ethical implications of controlling population sizes?"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"076878c5f495","_type":"block","asset":null,"children":[{"_key":"50bfe1efacc50","_type":"span","marks":[],"text":"When analyzing population growth curves, always:"}],"markDefs":[],"style":"normal"},{"_key":"4ceab7532e0b","_type":"block","asset":null,"children":[{"_key":"fb44d529b5480","_type":"span","marks":[],"text":"Describe the "},{"_key":"fb44d529b5481","_type":"span","marks":["strong"],"text":"three phases"},{"_key":"fb44d529b5482","_type":"span","marks":[],"text":" (exponential, transitional, plateau)."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"0f423ee82855","_type":"block","asset":null,"children":[{"_key":"a9bd440bb6990","_type":"span","marks":[],"text":"Explain how "},{"_key":"a9bd440bb6991","_type":"span","marks":["strong"],"text":"factors like predation, competition, and disease"},{"_key":"a9bd440bb6992","_type":"span","marks":[],"text":" modify the curve."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## Reflection and Review [block_67] 1. **How do density-dependent factors (e.g., predation, competition, and disease) shape population growth curves?** 2. **Why does exponential growth never last indefinitely in real populations?** 3. **What are some real-world examples of populations that follow a sigmoid growth curve?** [{"_key":"654a80e3910a","_type":"block","asset":null,"children":[{"_key":"505b2e2270e80","_type":"span","marks":[],"text":"Try sketching a population growth curve and labeling key phases and factors that influence it. Can you describe each phase in your own words?"}],"markDefs":[],"style":"normal"}]