ecology

• Abiotic factors are nonliving, e.g. temperature, climate, light and water availability, topology
• The photic zone is the part of a body of water that gets sunlight
• All aquatic photosynthesis occurs in the photic zone Image from OpenStax, CC BY 4.0
• The aphotic zone includes only animals and other heterotrophs Image from OpenStax, CC BY 4.0
• Air is 80% nitrogen, 20% oxygen
• Biotic factors are living, e.g. population, community, ecosystem, biosphere, habitat, niche
• A population is a group of individuals of the same species living in the same area.
• A community is a group of populations living in the same area.
• An ecosystem is a community of interrelationships between organisms and with their physical environment.
• The biosphere is the regions of earth’s surface that contain living things The biosphere includes the atmosphere, hydrosphere, and lithosphere
• A habitat is the type of place where an organism usually lives This includes other organisms, as well as the physical and chemical environment.
• A niche describes all biotic and abiotic resources in the environment used by an organism.
• Basic population ecology terms Size: N, total number of individuals in population Density: total number of individuals per area or volume occupied Dispersion: how individuals in a population are distributed Age structure: description of the abundance of individuals of each age Survivorship curve: shows how mortality of individuals in a species varies during their lifetimes Note: Dispersions may be clumped, uniform, or random
• Survivorship curve types Type I: most individuals survive to middle age and die quicker after this age (human)Type II: length of survivorship is random (invertebrates-hydra)Type III: most individuals die young, with few surviving to reproductive age and beyond (oysters) """Survivorship Curves"", link, by Rayhusthwaite at English Wikipedia, CC BY 3.0"
• Biotic potential is the maximum growth rate under ideal conditions i.e. when there are unlimited resources and no restrictions
• Age at reproductive maturity, clutch size, frequency of reproduction, reproductive lifetime, survivorship of offspring to reproductive maturity contribute to biotic potential of a species
• Carrying capacity is the maximum number of individuals of a population that can be sustained by habitat
• Limiting factors prevent a population from reaching biotic potential
• Limiting factors can be: Density-dependent, i.e. more intense as population density increases Density-independent, i.e. no relation to population density Examples: Density-dependent: increased, spread of disease, parasites, predation Density-independent: natural disasters or big temp changes
• The intrinsic rate of growth is when the reproductive rate (r) is maximum i.e. at biotic potential
• Exponential growth occurs whenever the reproductive rate (r) is greater than zero Image from OpenStax, CC BY 4.0
• Logistic growth occurs when limiting factors restrict the population size to the carrying capacity of the habitat. Image from OpenStax, CC BY 4.0
• Population cycles are fluctuations in population size due to various limiting factors Ex: a population cycle of a predator (lynx) and prey (hare) Image from OpenStax, CC BY 4.0
• Exponential and logistic growth patterns have two kinds of life-history: K-selected population: members have low reproductive rates and are roughly constant at K in sizeR-selected population: rapid exponential population growth K-selected example (sigmoidal growth curves): human population R-selected example: bacteria
• Human population growth is enabled by increase in food supply, reduction in disease, reduction in human wastes, and habitat expansion
• Ecological footprint is the amount of raw land necessary to sustain an individual’s lifestyle habits
• Species richness is the total number of different species present
• Relative abundance is the amount of individuals in each species
• Community ecology studies interactions between populations Ex: interspecific competition (competition between species)
• The competitive exclusion principle (Gause’s principle) states that if two species compete the same resources, one is likely to be more successful i.e. if they occupy the same niche
• Resource partitioning is when two species occupy the same niche but pursue slightly different resources or secure resources in different ways This way, individuals minimize competition and maximize success
• Character displacement is divergence of features as a result of resource partitioning This is also known as niche shift, and it reduces competition. For example, the mating calls of 2 species of frogs are different when they occupy the same island. On separate islands, the mating calls are the same.
• A realized niche is the niche that an organism occupies when there is competition Example: One barnacle species can live on rocks that are exposed to a full range of tides (fundamental). In the natural environment, a second species of barnacle outcompetes the first, but only at lower tide levels where desiccation is minimal. The first species then only survives in its realized niche, the higher tide levels.
• A fundamental niche is what an organism occupies when there is no competition Example: One barnacle species can live on rocks that are exposed to a full range of tides (fundamental). In the natural environment, a second species of barnacle outcompetes the first, but only at lower tide levels where desiccation is minimal. The first species then only survives in its realized niche, the higher tide levels.
• A predator is any animal that totally or partly consumes another organism True predator: kills and eats another animal. Parasite: spends most of its life living on host Parasitoid: an insect that lays its eggs on a host for larvae to consume Herbivore: an animal that eats plants
• Symbiosis is intimate, often permanent association between two organisms Commensalism (+/o) – one benefits, the other is unaffected Mutualism (+/+) – both organisms benefit Parasitism (+/-) – benefits at the expense of the host; include ecto- or endoparasites Commensalism examples: Remora and shark - remora gets food shark discards Barnacle and whale - barnacle gets wider feeding opportunities Mutualism examples: Gut bacteria - bacteria get food, we get vitamin K
• Saprophytism is feeding on dead organic matter Nutrients are digested externally.
• Scavengers consume dead animals directly Ex: vultures, hyenas, bacteria of decay
• Arthropods excrete solid uric acid crystals to conserve water
• Cold-blooded (aka poikilothermic) describes the vast majority of plants and animals; body temp. is close to that of surroundings This means metabolism is radically affected by environmental temperatures.