Ecosystem diversity in the context of "Biologically diverse"

Biodiversity is the variability of life on Earth. It can be measured on various levels, for example, genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth—it is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.

Since life began on Earth, six major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic aeon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion. In this period, the majority of multicellular phyla first appeared. The next 400 million years included repeated, massive biodiversity losses. Those events have been classified as mass extinction events. In the Carboniferous, rainforest collapse may have led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years.

Phoresis or phoresy is a temporary commensalistic relationship when an organism (a phoront or phoretic) attaches itself to a host organism solely for travel. It has been seen in ticks and mites since the 18th century, and in fossils 320 million years old. It is not restricted to arthropods or animals; plants with seeds that disperse by attaching themselves to animals are also considered to be phoretic.

Phoresis is rooted in the Greek words phoras (bearing) and phor (thief). The term, originally defined in 1896 as a relationship in which the host acts as a vehicle for its passenger, clashed with other terminology being developed at the time, so constraints on the length of time, feeding, and ontogeny are now considered. Phoresis is used as a strategy for dispersal, seasonal migration, transport to new host/habitat, escaping ephemeral habitats, and reducing inbreeding depression. In addition to the benefits afforded to individuals and species, its presence can add to the ecological diversity and complexity of an ecosystem.