Ecosystems and Populations Notes PDF

**Environment:** where an organism lives, it is comprised of both biotic (living) and abiotic (non-living) components **Ecology:** the study of the relationships of living things to one another and the environment **Ecosystem**: The resident biological community plus\ the abiotic components (rock,...

**Environment:** where an organism lives, it is comprised of both biotic (living) and abiotic (non-living) components **Ecology:** the study of the relationships of living things to one another and the environment **Ecosystem**: The resident biological community plus\ the abiotic components (rock, air, water, soil, etc)\ and the fluxes of matter and energy between them. **Population**: a group of similar organisms in the same place at the same time\ \ **Community**: a group of interacting populations in the same place at the same time Change is a constant process in nature. Everything is interconnected. **Factors that influence population size** - **Resource availability** (food, H2O, *etc*.) - **competition** (among members of a pop usually for a limited resource) - **Interspecific interactions** (predation, parasitism, etc.) - **conditions of the environment** (weather, fire) **Density-dependent fluctuation**: when a population size fluctuates in response to the density of another population; example: predator/prey relationships **Density-independent fluctuation**: when a population size fluctuates in response to something in the environment like climate or fire. **Carrying capacity (K):** the point at which there is a stable population (births = deaths). The resources in the environment can only support a certain number of individuals. Also known as density-dependent equilibrium. Exponential growth curve showing spotted salamanders over time in study area: **Life history strategy**: two different strategies for growing, surviving, reproducing **R-selected species**: devote a lot of time to reproduction and little to growth. They typically live in harsh environments where large pop sizes are an advantage. Characteristics are: rapid development, early maturity, small body size, short life, early birth, large number of offspring, minimal parental care. (American toad) **K-selected species**: devote a lot of time to growth and little to reproduction. They typically live in stable environments where survival is largely determined by competition for resources. Characteristics are slow development, delayed reproduction, large body size, long life, repeated reproduction, few offspring, good parental care (animals care, plants produce seed with stored food). (Bear) **Recall:\ \ Ecosystems include the\ \ resident biological community\ +\ the abiotic components of the environment\ \ and the fluxes of matter and energy between them.\ ** **Interacting and interdependent!** **Energy flow**: the flow of energy (calories) through an ecosystem begins with photosynthesis (PS) Photosynthesis: Green plants capture solar energy and convert it to chemical energy  Carbon is transferred from the atmosphere to the biosphere during photosynthesis (PS). The leaf surface is the interface between the atmosphere and the biosphere. The carbon from CO~2~ gets incorporated into plant and animal tissue. This tissue is called biomass. Biomass is usually measured in grams of carbon per square meter per year: gC/m²/yr  **Gross Primary Production (GPP)**: the total PS in the system **Net Primary Production (NPP)**: PS-Respiration (units are typically g of carbon/m²/year) **autotroph** (primary producer): the photosythesizers (the plants!) **heterotroph**: consumer **herbivores** **(primary consumers):** plant eaters **carnivores, parasites of animals (secondary consumers)** **decomposers**: break down organic matter **food web**: all of the above interconnected **trophic level**: the level occupied in the food web NPP is net primary production NPP = GPP -- R Trophic pyramid:  **More commonly, however, producers and consumers are connected in intricate [food webs] with some consumers feeding at several trophic levels.** **....complicated feeding patterns within ecosystems, in which a single species may consume a variety of other creatures and in turn serve as prey for multiple predators.**  **Ecosystem productivity (NPP in g/m²/year**): - tropical forests (warm and wet!) 1000-3500 - temperate forests 600-2500 - shrublands 700-1500 - desert grasslands 200-300 - tundra (cold and dry!) 100-250 **most primary production in the oceans is done by microscopic algae (phytoplankton).** **In the oceans, light and nutrients are important controlling factors for productivity.** **Biogeochemical cycles:** the cycling of chemical elements required by life\ between the living and non-living parts of the environment. **[Source] and [sink]** are often used when referring to nutrient cycling. A [source] is a part of the cycle that produces the element. A [sink] is a part of the cycle that removes it from the cycle. [Flux] refers to movement between sources and sinks. **Carbon cycle:** The three main reservoirs of carbon storage are:\ atmosphere, land (biosphere and lithosphere), oceans. Carbon cycles between these three reservoirs. Fossil fuels are considered a 4^th^ reservoir, but, here carbon is only extracted, not cycled back.  The atmosphere is only about 0.04% CO~2~! Carbon Dioxide in the atmosphere varies on different scales: diurnal, seasonal, annual, centennial and millennial You can measure these fluctuations in the atmosphere. Over the last century there has been a measurable change in the concentration of atmospheric CO~2~ from 280 to over 400 ppm due to fossil fuel emissions.  Every year there is a measurable increase in the concentration of atmospheric CO~2~ due to fossil fuel use.  CO~2~ is constantly both entering and exiting the ocean. Using the term "**net sink**" tells us that more carbon dioxide enters the ocean than leaves the ocean. The same is true for forests. **Nitrogen:** **Why care about nitrogen (N)?** **Nitrogen is an essential constituent of protein, DNA, RNA, chlorophyll.** **We need it!** **The tricky part is that nitrogen is abundant in the atmosphere (about 78%) but occurs in an inert form that living organisms cannot use directly.** **In the nitrogen cycle, some of this supply is converted to biologically useful forms.** **Simplified Nitrogen Cycle:** (The goal is to get usable nitrogen from the air into the soil so it can be absorbed by plants and enter the food chain.)  **Another way of getting usable nitrogen into the soil is through the decomposition of proteins found in dead plants and animals:** **Nitrogen is returned to the atmosphere in the process called denitrification: another species of bacteria converts nitrate (NO~3~) to atmospheric nitrogen (N~2~).** **Humans add Nitrogen to the cycle primarily through fertilizer use.** **Interspecific interactions in communities:** Predation +/- Parasitism +/- Competition -/- Commensalism +/o Mutualism +/+