The structure of the nests themselves are subject to the forces of natural selection. Moreover, a nest can survive over successive generations, so that progeny inherit both genetic material and a legacy niche that was constructed before their time. Biomes are larger units of organization that categorize regions of the Earth's ecosystems, mainly according to the structure and composition of vegetation.
Biomes include tropical rainforest , temperate broadleaf and mixed forest , temperate deciduous forest , taiga , tundra , hot desert , and polar desert. To a microbe , the human body is a habitat and a landscape.
The oceanic microbiome plays a significant role in the ecological biogeochemistry of the planet's oceans. The largest scale of ecological organization is the biosphere: the total sum of ecosystems on the planet. Ecological relationships regulate the flux of energy, nutrients, and climate all the way up to the planetary scale. For example, the dynamic history of the planetary atmosphere's CO 2 and O 2 composition has been affected by the biogenic flux of gases coming from respiration and photosynthesis, with levels fluctuating over time in relation to the ecology and evolution of plants and animals.
Population ecology studies the dynamics of species populations and how these populations interact with the wider environment. A primary law of population ecology is the Malthusian growth model  which states, "a population will grow or decline exponentially as long as the environment experienced by all individuals in the population remains constant. An example of an introductory population model describes a closed population, such as on an island, where immigration and emigration does not take place.
Hypotheses are evaluated with reference to a null hypothesis which states that random processes create the observed data. In these island models, the rate of population change is described by:. Using these modelling techniques, Malthus' population principle of growth was later transformed into a model known as the logistic equation :.
Population ecology builds upon these introductory models to further understand demographic processes in real study populations. Commonly used types of data include life history , fecundity , and survivorship, and these are analysed using mathematical techniques such as matrix algebra.
The information is used for managing wildlife stocks and setting harvest quotas. The concept of metapopulations was defined in  as "a population of populations which go extinct locally and recolonize". Animal migration is set apart from other kinds of movement; because, it involves the seasonal departure and return of individuals from a habitat.
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Plant ecologists use pollen records that accumulate and stratify in wetlands to reconstruct the timing of plant migration and dispersal relative to historic and contemporary climates. These migration routes involved an expansion of the range as plant populations expanded from one area to another.
There is a larger taxonomy of movement, such as commuting, foraging, territorial behaviour, stasis, and ranging. Dispersal is usually distinguished from migration; because, it involves the one way permanent movement of individuals from their birth population into another population.
In metapopulation terminology, migrating individuals are classed as emigrants when they leave a region or immigrants when they enter a region , and sites are classed either as sources or sinks. A site is a generic term that refers to places where ecologists sample populations, such as ponds or defined sampling areas in a forest. Source patches are productive sites that generate a seasonal supply of juveniles that migrate to other patch locations. Sink patches are unproductive sites that only receive migrants; the population at the site will disappear unless rescued by an adjacent source patch or environmental conditions become more favourable.
Climate change and biodiversity
Metapopulation models examine patch dynamics over time to answer potential questions about spatial and demographic ecology. The ecology of metapopulations is a dynamic process of extinction and colonization. Small patches of lower quality i. A dynamic metapopulation structure evolves from year to year, where some patches are sinks in dry years and are sources when conditions are more favourable. Ecologists use a mixture of computer models and field studies to explain metapopulation structure.
Community ecology is the study of the interactions among a collections of species that inhabit the same geographic area. Community ecologists study the determinants of patterns and processes for two or more interacting species. Research in community ecology might measure species diversity in grasslands in relation to soil fertility. It might also include the analysis of predator-prey dynamics, competition among similar plant species, or mutualistic interactions between crabs and corals.
Tansley  : Ecosystems may be habitats within biomes that form an integrated whole and a dynamically responsive system having both physical and biological complexes. Ecosystem ecology is the science of determining the fluxes of materials e. Ecosystem ecologist attempt to determine the underlying causes of these fluxes. This requires an understanding of the community connections between plants i.
Migration of Organisms
The underlying concept of ecosystem can be traced back to in the published work of George Perkins Marsh "Man and Nature". Differences stem from the nature of the unique physical environments that shapes the biodiversity within each. A more recent addition to ecosystem ecology are technoecosystems , which are affected by or primarily the result of human activity. A food web is the archetypal ecological network. Plants capture solar energy and use it to synthesize simple sugars during photosynthesis.
As plants grow, they accumulate nutrients and are eaten by grazing herbivores , and the energy is transferred through a chain of organisms by consumption. The simplified linear feeding pathways that move from a basal trophic species to a top consumer is called the food chain. The larger interlocking pattern of food chains in an ecological community creates a complex food web.
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Food webs are a type of concept map or a heuristic device that is used to illustrate and study pathways of energy and material flows. Food webs are often limited relative to the real world. Complete empirical measurements are generally restricted to a specific habitat, such as a cave or a pond, and principles gleaned from food web microcosm studies are extrapolated to larger systems. Food webs exhibit principles of ecological emergence through the nature of trophic relationships: some species have many weak feeding links e. Theoretical and empirical studies identify non-random emergent patterns of few strong and many weak linkages that explain how ecological communities remain stable over time.
This increases food web stability.
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Biodiversity within ecosystems can be organized into trophic pyramids, in which the vertical dimension represents feeding relations that become further removed from the base of the food chain up toward top predators, and the horizontal dimension represents the abundance or biomass at each level. Species are broadly categorized as autotrophs or primary producers , heterotrophs or consumers , and Detritivores or decomposers.
Autotrophs are organisms that produce their own food production is greater than respiration by photosynthesis or chemosynthesis. Heterotrophs are organisms that must feed on others for nourishment and energy respiration exceeds production. It has been suggested that omnivores have a greater functional influence as predators, because compared to herbivores, they are relatively inefficient at grazing.
Trophic levels are part of the holistic or complex systems view of ecosystems.
This has led some ecologists to "reiterate that the notion that species clearly aggregate into discrete, homogeneous trophic levels is fiction. A keystone species is a species that is connected to a disproportionately large number of other species in the food-web. Keystone species have lower levels of biomass in the trophic pyramid relative to the importance of their role. The many connections that a keystone species holds means that it maintains the organization and structure of entire communities.
The loss of a keystone species results in a range of dramatic cascading effects that alters trophic dynamics, other food web connections, and can cause the extinction of other species. Sea otters Enhydra lutris are commonly cited as an example of a keystone species; because, they limit the density of sea urchins that feed on kelp. If sea otters are removed from the system, the urchins graze until the kelp beds disappear, and this has a dramatic effect on community structure.
Ecosystems, Ecosystem Services, and Biodiversity - Fourth National Climate Assessment
It is difficult to experimentally determine what species may hold a keystone role in each ecosystem. Furthermore, food web theory suggests that keystone species may not be common, so it is unclear how generally the keystone species model can be applied. Complexity is understood as a large computational effort needed to piece together numerous interacting parts exceeding the iterative memory capacity of the human mind.
Global patterns of biological diversity are complex.
Related Migration of Organisms: Climate Geography Ecology
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