Notes on ecology

Ecology is the scientific study of organisms and their interactions with each other and the environment. These are my notes on ecology from BIO 1010.

Early ecology

Carl Linnaeus was one of the most influential and earliest ecologists who developed the binomial nomenclature system for naming species. Charles Darwin improved on ecology by describing the distribution and abundance of plants and animals, as well as the interactions between species. He realized that evolution is driven by the ecology of an environment. Ernest Haeckel becomes the first to call the field ecology. Ellen Richards brings ecology to the US, and becomes one of the first proponents of the sustainable stewardship of the environment.

Ecological models

We use models to understand the complex dynamics of ecology. Common ecological models include:

We can then consider both biotic (living) and abiotic (non-living) factors in an environment. Abiotic factors include:

Whereas biotic factors include:

Biomes

Biomes are defined by a specific temperature and precipitation, and determine the organisms that grow. There are many different types of biomes, ranging from the tropical forest to arboreal to deep sea hydrothermal vents. Climates and biomes are very closely connected.

Climate

Water in constant motion in currents are crucial to regulating Earth's temperature. The Gulf Stream distributes heat from equatorial latitudes to North America and northern Europe.

Atmospheric circulation also affects winds, rainfall, and temperature. The global circulation of the rotating splits the atmosphere into 3 cells:

Atmospheric circulation distributes heat around the Earth, allowing different biomes to form and cause different species to evolve.

Seasonal climatic effects are due to the tilt of the Earth. This causes different parts of the Earth to receive different amounts of sunlight during different times of the year.

Biodiversity

Biodiversity is the number of types of species per unit area. Biodiversity is impacted by the latitude - high biodiversity is situated around the equator and low biodiversity is around the poles. The productivity and stabilization hypothesis is used to explain this difference in biodiversity:

Biomass

Sunlight is the source of energy for almost all ecosystems on Earth. Plants use 400-700 nm wavelength electromagnetic waves for photosynthesis.

Biomass can be measured in several different ways:

Biomass measurementDescription
Standing cropTotal plant biomass in an ecosystem
Gross Primary Production (GPP)Total amount of energy fixed by plants
Net Primary Production (NPP)Energy remaining after plants have met their own energetic needs
RespirationGPP - NPP

Continental regions of oceans, such as algal beds and reefs have higher productivity than open ocean, and in general, high sunlight, nutrient, temperature and moisture regions, such as swamps and rainforest, have higher productivity as well.

Carbon cycle

Carbon sources include emissions from burning fossil fuels, forest fires, and respiration. Carbon sinks include the oceans, plants, and soil.

No transfer is 100% efficient, some energy is always lost as heat. Because of the laws of thermodynamics, the ongoing existence of the biosphere depends on a constant flow of energy from producers to consumers.

The number of species

The first calculation of global biodiversity was made by John Westwood in 1833, who arrived at the conclusion of 400,000 insect species on the planet. In 1998, Robert May calls for a global effort to find and describe all living species. There are approximately 1.8 million named species, and it's likely there are far more yet to be discovered - approximately 5 million non-microbial species.

Populations

Species' populations are determined by 3 factors:

Populations grow through birth and migration in, and decline through death and migration change. The population change equation is:

$$ \Delta P = (B - D) + \Delta M $$ Populations are typically stable in environments without human interference. This is due to territoriality. Unstable populations are usually dependent on a certain factor, such as nutrient limitations. Some populations show exponential growth, but that is not sustainable, and once an organism exceeds the carrying capacity of its environment, the entire population dies off. Other populations show logistic growth, where environmental resistance (such as predators, competition, drought, etc.) brings population within carrying capacity.

Ecosystem Dynamics

The first principle of ecosystem dynamics is that everything is ultimately connected to everything else. To understand ecosystems we need to adopt both reductionist and holistic approaches.

The idea of feedback is a process in which the output of a system eventually affects its input. It can cause amplification of output (positive feedback) or diminishing of output (negative feedback).

The Gaia Hypothesis states that the life and physical evolve together as a connected system each influencing and shaping the other. The environment is regulated by all life such as to self-regulate and maintaining itself to sustain life. It could be said that the Earth itself becomes homeostatic. The Daisy World simulation was proof that feedback from living organisms could regulate a planet's environment.

Competition

Resources are limited, and so if one species uses one resources, there are less resources available for another species. Thus, competition leads to a decrease in abundance in all species

InterferenceExploitativeApparent
Species fighting over and blocking each other's access to limited resourcesMultiple species use the same resource, but one is more efficientTwo species share the same predator

Competition can be between species, or interspecies, or within the same species, or intraspecies. Competition is minimized when each species occupies a particular niche, when each species is spatially separated or distributed, and when species' activity occur during specific times. Competition increases with niche expansion. This is why character displacement occurs - to reduce competition and thus improve survival rates, species are driven to different ends, which manifests in adaptive radiation.

The competitive exclusion principle

When species are grown within a lab separately, then two species will reach similar populations. Meanwhile, when species are grown within a lab together, one species dominates and the other species diminishes in population. This is known as competitive exclusion. Therefore, if two or more species live together, they must possess different ecological niches.

Predation

Predators have very specific adaptations to help them hunt:

Predator and prey have a cycle. This is because predators control the prey population top-down, and food controls the prey population bottom-up.

Parasitism

Parasitism is when one organism is adapted to live in another species and use another species for its life processes. Parasites often cause harm to the host and decrease the distribution and abundance of hosts. They can also change the behavior of the host.

Mutualism

Mutualism is where two or more species benefits from associating with each other.

There are two types of mutualism:

There are several benefits of mutualism:

Commensalism

Commensalism is when one species gains benefit while another species neither benefits nor is harmed.

Symbiosis

Symbiosis is any interaction between two dissimilar species acting in unison. It includes mutualism, commensalism, and parasitism.

Keystone species

Keystone species are species that has a disproportionate impact on an ecosystem, such that if they were removed the ecosystem would change drastically. Examples include:

When keystone species are removed, there may be disastrous effects. For instance, in kelp ecosystems in Alaska in the 1990s, biodiversity greatly decreased due to overfishing. This lead to:

Extreme conditions

Threats to biodiversity

Species richness can be affected by:

Increasing area 10x increases biodiversity 2x. Thus, habitat fragmentation causes ecosystems to be vulnerable. Minor disturbances lead to increases in species and maintains diversity. Disturbances lead to two stages of recovery - first, primary succession, when resistant plants begin to colonize a location, and then secondary succession, where other plants and animals move in. Succession never ends and there is no "stable state", but in time the environment recovers or even exceeds the biodiversity it once had. The intermediate disturbance hypothesis postulates that there is an ideal size of disturbances that is most conducive to biodiversity, as low-level disturbances do not create enough niches and competitive exclusion limits biodiveristy, while high-level disturbances lead to high stress and rates of extinction.

Global ecological dilemmas

Invasive species

Invasive species are species that are not native a habitat, and do not have any native predators. They either outcompete or prey on species in the habitat they are introduced into. Invasive species can upset ecosystems as they are not sufficiently limited by the limiting factors of their new ecosystem.

Invasive species can be managed in four stages:

Biological control can sometimes be used to control invasive species. For instance, the prickly pear cactus was once an invasive species in Australia. The introduction of moth larvae from its native habitat allowed the population to be controlled.

However, in other cases, biological control can introduce more problems. For example, the cane toad was introduced to reducing beetle populations that fed on cane toads.

Water security

Eutrophication is when excessive nutrients in a body of water causes dense growth of algae and starves animals of oxygen. Dead zones, or regions in which water is oxygen-depleted, can cause mass die-offs and disrupted aquatic habitats. In addition, various forms of algae can make the water toxic. Causes of eutrophication include overuse of fertilizers, industrial agriculture and animal farming.

Salinization is when freshwater has increased salt concentrations due to road deicers, irrigation runoff, and sewage.

Climate change

Climate change is the long-term change in the Earth's overall temperature. In 1900, chemist Svante Arrhenius discovers the greenhouse effect. In 1958, Revelle & Keeling found that there is an upwards trend in atmospheric CO2 concentration.

Greenhouse gases include:

Climate change leads to:

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