Ecological niche in the context of "Spirochetes"

A species (pl. species) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. It can be defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour, or ecological niche. In addition, palaeontologists use the concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses) are given a two-part name, a "binomen". The first part of a binomen is the name of a genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature, also sometimes in zoological nomenclature). For example, Boa constrictor is one of the species of the genus Boa, with constrictor being the specific name.

While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clonal lineage is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be a perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that a fossil lineage should be divided into multiple chronospecies, or when populations have diverged to have enough distinct character states to be described as cladistic species.

The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 542 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

The time span of the Phanerozoic starts with the sudden appearance of fossilised evidence of a number of animal phyla; the evolution of those phyla into diverse forms; the evolution of plants; the evolution of fish, arthropods and molluscs; the terrestrial colonization and evolution of insects, chelicerates, myriapods and tetrapods; and the development of modern flora dominated by vascular plants. During this time span, tectonic forces which move the continents had collected them into a single landmass known as Pangaea (the most recent supercontinent), which then separated into the current continental landmasses.

In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ecological niche. Thus "habitat" is a species-specific term, fundamentally different from concepts such as environment or vegetation assemblages, for which the term "habitat-type" is more appropriate.

The physical factors may include (for example): soil, moisture, range of temperature, and light intensity. Biotic factors include the availability of food and the presence or absence of predators. Every species has particular habitat requirements, habitat generalist species are able to thrive in a wide array of environmental conditions while habitat specialist species require a very limited set of factors to survive. The habitat of a species is not necessarily found in a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss; a parasitic organism has as its habitat the body of its host, part of the host's body (such as the digestive tract), or a single cell within the host's body.

Plankton are organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). Marine plankton include drifting organisms that inhabit the saltwater of oceans and the brackish waters of estuaries. Freshwater plankton are similar to marine plankton, but are found in lakes and rivers. An individual plankton organism in the plankton is called a plankter. In the ocean plankton provide a crucial source of food, particularly for larger filter-feeding animals, such as bivalves, sponges, forage fish and baleen whales.

Plankton includes organisms from species across all the major biological kingdoms, ranging in size from the microscopic (such as bacteria, archaea, protozoa and microscopic algae and fungi) to larger organisms (such as jellyfish and ctenophores). This is because plankton are defined by their ecological niche and level of motility rather than by any phylogenetic or taxonomic classification. The plankton category differentiates organisms from those that can swim against a current, called nekton, and those that live on the deep sea floor, called benthos. Organisms that float on or near the water's surface are called neuston. Neuston that drift as water currents or wind take them, and lack the swimming ability to counter this, form a special subgroup of plankton. Mostly plankton just drift where currents take them, though some, like jellyfish, swim slowly but not fast enough to generally overcome the influence of currents.

There are several plausible pathways that could lead to plant and animal species extinction from climate change. Every species has evolved to exist within a certain ecological niche, but climate change leads to changes of temperature and average weather patterns. These changes can push climatic conditions outside of the species' niche, and ultimately render it extinct. Normally, species faced with changing conditions can either adapt in place through microevolution or move to another habitat with suitable conditions. However, the speed of recent climate change is very fast. Due to this rapid change, for example cold-blooded animals (a category which includes amphibians, reptiles and all invertebrates) may struggle to find a suitable habitat within 50 km of their current location at the end of this century (for a mid-range scenario of future global warming).

Climate change also increases both the frequency and intensity of extreme weather events, which can directly wipe out regional populations of species. Those species occupying coastal and low-lying island habitats can also become extinct by sea level rise. This has already happened with Bramble Cay melomys in Australia. Finally, climate change has been linked with the increased prevalence and global spread of certain diseases affecting wildlife. This includes Batrachochytrium dendrobatidis, a fungus that is one of the main drivers of the worldwide decline in amphibian populations.

Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin and contains essential nutrients such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells to provide energy, maintain life, or support growth. Different species of animals have different feeding behaviours that satisfy the needs of their metabolisms and have evolved to fill specific ecological niches within specific geographical contexts.

Omnivorous humans are highly adaptable and have adapted to obtaining food in many different ecosystems. Humans generally use cooking to prepare food for consumption. The majority of the food energy required is supplied by the industrial food industry, which produces food through intensive agriculture and distributes it through complex food processing and food distribution systems. This system of conventional agriculture relies heavily on fossil fuels, which means that the food and agricultural systems are one of the major contributors to climate change, accounting for as much as 37% of total greenhouse gas emissions.

In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a testa. More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote and grows within the mother plant to a certain size before growth is halted.

The formation of the seed is the defining part of the process of reproduction in seed plants (spermatophytes). Other plants such as ferns, mosses and liverworts, do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates.

Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations. The first seabirds evolved in the Cretaceous period, while modern seabird families emerged in the Paleogene.

Seabirds generally live longer, breed later and have fewer young than other birds, but they invest a great deal of time in their young. Most species nest in colonies, varying in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even on each other. Seabirds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely.