Unit 8: Ecology

Ecology is all about the interactions that organisms have amongst themselves and with their environment. This can be seen on a small scale, within populations, and on larger scales, in ecosystems and across the globe. The relationships that exist between organisms are complex and ever changing. We are constantly responding to our environment and those around us. Some of the largest problems plaguing our planet right now are the largest culprits to the changing landscape of ecosystems across the globe. All of these issues come together in the awesome unit of Ecology.

Browse slides from the stream 'Nutrient Cycles & Succession.'

In today’s live stream, we discussed various nutrient cycles and ecological succession. We started by talking about the role and importance of nutrients, specifically carbon, nitrogen, and phosphorus. We then talked about how water transforms within a cycle, reviewing that precipitation occurs when water from the air turns into a liquid on the ground, that evaporation occurs when liquid water evaporates into the air, that condensation occurs when water vapor turns into liquid droplets, and that transpiration occurs when plants lose water through their stomata. Next, we discussed the carbon cycle. The carbon cycle starts with the cellular respiration of plants and animals who release carbon dioxide into the air. Next, through photosynthesis, carbon dioxide is incorporated into the plants’ biochemistry, and when the plants become a food source for consumers, the carbon goes through the food chain. Through cellular respiration of the consumers, the carbon enters the air again. In the nitrogen cycle, bacteria first go through fixation to turn the nitrogen in the air into ammonia in the soil. Through other bacteria, the ammonia is then changed to nitrate through nitrification. Now the plants can absorb the nitrates and ammonia through their roots resulting in the nitrogen becoming a part of their bodily functions. If they get eaten, the nitrogen then gets transferred to the consumer until finally, an animal dies and decomposes, putting the nitrogen back into the soil. The nitrogen can also go back into the air when the denitrifying bacteria turn the nitrates into atmospheric nitrogen. In the phosphorus cycle, plants suck up the phosphorus in the soil. When they get eaten, the phosphorus, like nitrogen, gets transferred to the consumer who uses to make ATP or other macromolecules. When they die, the phosphorus gets returned into the soil and the cycle starts again. Next, we talked about succession, both the primary and the secondary kinds. Primary succession is when there is no soil available in the beginning, but eventually, after the soil is created, life would start occurring. Secondary succession is when soil already exists in the environment and just the life existing before was killed by a natural disaster, like a fire. This means that life can grow easily in the environment because the nutrient-rich soil already exists. After discussing how species diversity, defined in terms of species richness and relative abundance, works for a little bit, we talked about invasive species and how they might have decreased the species diversity of an environment. Finally, we end the session by answering a couple of questions from the chat both relating to nutrient cycles and succession and relating to other topics in biology like DNA replication.

Live Stream Notes: In this live stream, we discuss community ecology. We learn that community ecology is the relationship among different species in the same environment. We start by discussing energy and how it flows through the trophic levels. Trophic levels consist of the producers (like plants and algae), primary consumers (like deer and rabbits), secondary consumers (like snakes), and tertiary consumers (like hawks and sharks). As we move up the trophic levels, we see that 90% energy is “lost” as heat per a level so the next level up only gets 10% of the previous trophic level’s energy. This is why tertiary consumers eat so much than secondary consumers. On the other hand, producers make up the largest portion of the food web and the energy pyramid. When a secondary consumer species is removed from an environment, the food source may be decreased for the tertiary consumers leading to a decrease in population while there would be overpopulation of the primary consumers and maybe even depletion of the producers. This species, usually near the top of the food web, would be a keystone species because it has a drastic impact on the food chain. We also learned that there are 3 relationships species can have other than predator and prey, parasitism (one benefits, one hurts), commensalism (one benefits, one does not have effects), and mutualism (both benefit). After doing 2 FRQ questions, we end the session by discussing the difference between commensalism and mutualism.

Browse slides from the stream 'Community Ecology,' where we cover topics including Ecology.

Browse slides from the stream 'Population Ecology.'

In this session, we cover aspects of population ecology. We learn that ecology is the study of interactions organisms have with their environments and with each other. In addition, we look at how to calculate population growth with three simple math problems and discuss the differences between exponential and logistic growth. Furthermore, we review abiotic (nonliving) and biotic (living) factor examples, such as temperature, rocks, light, and plants. We end the session with an idea of how density dependent and density independent factors differ, followed by a practice problem that illustrates how to calculate carrying capacity.

Organisms have highly evolved mechanisms of responding to their environment. These responses may be behavioral, such as finding higher ground during a rainstorm, or physiological, such as an increase in epinephrine during a high-stress situation. A number of environmental factors, such as changing temperature, weather patterns, an increase or decrease in food or water, or a decrease in a shelter can lead to changes within an organism. Many organisms are dependent on the seasons, hibernating or migrating in winter. These mechanisms and responses help them to survive and reproduce.

All organisms in an ecosystem need energy. Remember, all the energy that we have on earth originates from the sun. Photosynthetic bacteria convert this energy into usable energy through photosynthesis. Energy flows through ecosystems, starting with energy from the sun and traveling through photosynthetic organisms and the organisms that consume them. The majority of energy is lost in the form of heat between levels of the ecosystem. This is because energy is used by the individual in order to produce heat, digest, and go through basic daily functioning.

A population is defined as a group of the same species living in the same area. An example of this would be humans living in Chicago. Within a population, there are a number of factors that affect the health and growth of the species. 

Populations are often affected by factors that inhibit their ability to continue to survive and reproduce. These factors may be broken into two categories: density-dependent factors and density-independent factors.

A community refers to a group of different populations living in the same area. An example of this would be humans, dogs, and rats living in the city of Chicago. A community has many interactions between the populations of species that live there. These interactions can be positive, negative, or neutral. When studying a community, scientists often measure the species diversity and species composition in that area. This refers to the number of unique species living in the area and what percent of the population is represented by each species. A species with a large number of unique species with equally distributed populations would be considered highly diverse.

Biodiversity refers to the amount of diversity in species and within species in an ecosystem. Ecosystems with a higher level of biodiversity are better able to respond to changes in their environment. This is due to the increase in potential defenses to various problems. For example, if a highly diverse population is infected with a specific pathogen, it is likely that at least a few individuals within the population possess some sort of immunity or enhanced ability to fight the pathogen. This allows the population to survive through the challenging environmental shift. Less diverse ecosystems may collapse if exposed to extreme changes in the environment or other detrimental events. Using the previous example, it is less likely that individuals within a population would possess immunity to the pathogen, and it is more likely that the entire population may be wiped out from the pathogen. An increase in genetic diversity always leads to an increase in protection from environmental changes. This concept is tested frequently on the AP exam.

Disruptions to ecosystems may lead to the process of evolution, as changes in the environment may lead to a selective advantage for some species over others. This process takes place if certain adaptations give organisms an advantage over others to survive and reproduce.