The rapidly increasing world population creates more need for shelter, transportation, energy, and nutrition, leading to the construction of new settlements and agricultural areas, making habitats fragmented, endangering many species and a significant portion of local populations. Biodiversity is adversely affected by the deterioration of the functioning, and the integrity of habitat ecosystems. Insects, which constitute an important part of the animal kingdom, and exist all over the globe, affect human life both directly and indirectly, and are an indispensable part of the food chain; yet insect diversity is also under serious threat. Anatolia is a land where rich habitat and climate diversity are observed, being as rich as the whole of continental Europe in terms of plant and insect diversity on its own. In this review, the origins of, and the contributing factors to, insect diversity in Turkey is examined through data on a few specific insect groups that dwell steppe, aquatic, cave, and mountainous regions.
Top1. Introduction
Insects are one of, arguably, the most important group of animals in the ecosystem (Klein et al., 2007). They play key roles in many processes, such as the spread of seeds, and pollination. They have a major impact on agriculture, and even in non-agricultural areas, both positively and negatively (FAO, 2021). They affect the water quality, act as a vector in the transport and transmission of certain diseases, and their role in the food chain is being the most important food source for many vertebrates (Reptiles, amphibians, birds, humans, etc.) (Prather et al., 2013). While the number of insect species discovered and published in the literature to date is only over one million, insects are the most common animal group in nature and are estimated to be represented by over 5 million species worldwide. While the calculations show that there exists a spreading of more than half a million insect species in the Palearctic region, which Turkey is a part of, it is predicted that there might exist 1.5 million species in the world belonging to the Coleoptera order, which would mean that this order has the most species diversity (Stork, 2018). Why are there so many species of insects? The most important reasons are: a) As it is generally known, insects have a small body size. b) Some insects are able to spread widely as a result of their ability to fly. c) As their life cycles are short, their reproductive capacity is very high. Some species exhibit the facultative embryonic diapauses, giving birth to new generations several times a year under favorable temperatures, and conditions. Others necessarily spend the winter in eggs and give birth to a new generation per year, while some species spend the winter in the final stage of nymph or juvenile form, then quickly become reproductively active in early spring. Some species exhibit summer egg diapause (e. g. Anacridium aegyptium, Orthoptera). d) One of the reasons for the high diversity in Coleoptera, Lepidoptera, Hymenoptera and Diptera is the elimination of the competition for food between the nymphal and the adult period as there is a complete metamorphosis (Holometabolism). e) Since insects are coated by chitin, they are protected against factors such as dehydration and microbes cannot enter their bodies. f) With wide topographical and climatic variety, natural selection gives way to increasingly fitter populations. The insect species that can adapt to many different habitats exhibit a wider variety. g) There exists a correlation between plant and insect diversity, as these lifeforms co-evolve, meaning that richer the diversity of plants is, richer the diversity of insects will be.
Before going into detail as to the main causes of the richness of species in insects, it will be useful to take a look at the general points on, and the main examples of the subject. The distribution of insects in an area is governed by factors such as food availability, suitability for reproductive activities, population density, and vulnerability to predation. These factors limit the distribution and population densities of the insects (le Roux et al., 2020). The body sizes of insects are related to these factors. Since insects have small body sizes, more than one insect species may survive and reproduce in small habitats, but due to competition and food requirements, habitats are often used by very few individuals of larger animal species (Bush & Butlin, 2004).