3.1: Species Diversity
In general, the first step in responding to the conservation need of a species or population is to know its identity. For this reason, one of the three main goals of conservation biology is to document all life on Earth or, in plain language, to give each species a name. The task of giving each species a (formal) name falls on specialist scientists known as taxonomists. Taxonomists (and the people assisting them) explore nature, collect specimens of plants, animals, and other organisms, describe/name those specimens, and store the specimens in permanent collections, such as natural history museums and herbaria (there are currently over 6,500 natural history museums in the world). These permanent collections, affectionally called “Libraries of Life”, provide the material and locations that taxonomists use to describe species and to develop systems for biodiversity classifications.
When a species is formally described, it is given a unique two-part name, known as a binomial name. For example, the binomial name for the lion is Panthera leo. The first part of the name, Panthera, identifies the generic epithet (or simply genus); in this case, the panthers or big cats. The second part of the name, leo, identifies a subset within the genus known as the specific epithet (or simply species); in this case, the lion. This binomial system thereby both identifies a lion as its own species and connects it to other closely-related species: Africa and Asia’s leopards (P. pardus, VU); Asia’s snow leopard (P. uncia, VU); Asia’s tigers (P. tigris, EN); and South America’s jaguars (P. onca, NT) (Figure 3.2).
Binomial species names, as well as the taxonomic relationships between different species, form the backbone of taxonomic databases, as compiled and organised by biodiversity informatics projects. Some biodiversity informatics projects focus on one group of species, while others focus on certain regions. For example, all known marine species are listed in the World Register of Marine Species ( http://www.marinespecies.org ), while the Catalogue of Afrotropical Bees ( https://doi.org/10.15468/u9ezbh ) collates information of only African bees. In some cases, multiple projects—each using different assumptions to suit different user groups better—may catalogue the same group of species. For example, the world’s fungi, are listed both in Index Fungorum ( http://www.indexfungorum.org ) and MycoBank ( http://www.mycobank.org ), while bird names are indexed by at least seven different projects, each a little different from the other. There are even some biodiversity informatics projects that attempt to catalogue all life on Earth; examples include Catalogue of Life ( http://www.catalogueoflife.org ), Encyclopaedia of Life ( http://eol.org ), and Wikispecies ( https://species.wikimedia.org ).
What is a species?
There are three rules of thumb that taxonomists use to describe a species:
- Morphological definition of species: Individuals that are distinct from other groups in their morphology, physiology, or biochemistry.
- Biological definition of species: Individuals that breed (or could breed) with each other in the wild, but do not breed with members of other groups.
- Evolutionary definition of a species: Individuals that share a common evolutionary past, usually indicated by genetic similarities.
In practice, conservation biologists generally rely on the morphological definition to identify species. The ability to recognize physical or morphological differences between organisms is handy even when the actual identity of specimens is unknown. In such cases, field biologists may refer to the unknown species as morphospecies (Figure 3.3), at least until an expert identifies the unknown individuals or a taxonomist gives them an official scientific name. In contrast, the biological definition of species relies on information that is difficult to obtain and thus not readily available. The biological definition also fails to recognize recent speciation, which can cause closely related but distinct species to interbreed. Similarly, it is generally impractical for fieldworkers to measure differences in genetic sequences to distinguish one species from another because these procedures currently require expensive, immovable laboratory equipment.
Taxonomists can use morphological, biological, and genetic information to identify species.
Despite the practical difficulties of applying the biological and evolutionary definitions in the field, both provide important guidelines for conservation efforts. The biological species definition allows us to better understand species biogeography and the mechanisms that prevent two closely-related species to interbreed. The evolutionary species definition in turn allows us to better understand how and why the genetic makeup of populations change over time, through processes such as random mutations, natural selection, emigration, and immigration. It is thus important for conservation biologists to acknowledge the importance of maintaining these dynamic processes in protecting natural systems, and where possible, include them in their fieldwork (Box 3.1).
Tammy Robinson and Clova Mabin
Centre for Invasion Biology, Stellenbosch University,
Stellenbosch, South Africa.
trobins@sun.ac.za , clovamabin@gmail.com
Trying to find threatened species in aquatic systems can be like trying to find a needle in a haystack. Traditionally, researchers have set off with nets, buckets, and even snorkels and scuba gear to painstakingly search for threatened species in ecosystems, ranging from streams to coral reefs. While searching in a small system, such as a pond, might not seem too difficult, it can be a real challenge to find tiny, inconspicuous organisms in and amongst the mud, stones, and plants, especially when they are trying their best to remain hidden. Things get even trickier when combing through large ecosystems like lakes or bays. These difficulties make it hard to reliably monitor the status or distribution of threatened aquatic species.
However, scientists have recently developed a new search tool called environmental DNA, (eDNA in short), where researchers collect and search water samples for the DNA of the species they are interested in. The eDNA technique was first developed by a biologist trying to detect organisms in sediment (Willerslev et al., 2003) but is now being used by conservationists working in all kinds of aquatic ecosystems. Organisms continually release small amounts of DNA into the water by sloughing off skin or other cells and releasing bodily wastes. This DNA then mixes in the surrounding environment, allowing those organisms to be detected through genetic analyses without actually sampling them directly.
Researchers have been testing just how useful eDNA is for finding threatened species in ponds and streams (Thomsen et al., 2012). They detected the eDNA of fish, shrimp, dragonflies, and amphibians in most ponds where the species were known to occur and found no trace of the eDNA of these species where they were absent. The most exciting development was their ability to detect eDNA evidence of threatened species in places where they had previously occurred but not been recently recorded by traditional search methods. Field observations and experiments also showed that eDNA can persist for up to two weeks in fresh water, and that concentrations can correspond to population sizes; this suggests that scientists may be able to monitor the abundance of rare aquatic species to a high degree of accuracy using this approach. For example, Lake Victoria could be searched for rare cichlid fish species that may still be present at low numbers even though researchers have not seen them for several years.
eDNA technology also holds considerable promise for the management of aquatic invasive species, if they could be detected as new arrivals before their numbers grow enough to be detected by conventional methods (Takahara et al., 2013). Early detection will give conservation managers a head-start and enable them to react quickly to invasions and increase their chances of preventing the environmental damage associated with invasive species. In a local twist to the tale, ongoing work in South Africa is applying eDNA as a tool for measuring the success of management efforts aimed at removing the invasive marine European shore crab (Carcinus maenas) (Figure 3.A) that could outcompete or threaten native African marine species. It is hoped that eDNA will be able to track the decline in crab numbers as the species is removed and then be used to monitor for any new arrivals should the crabs re-invade.
This exciting new approach in detecting species is rapidly developing and improving our efficiency at monitoring threatened and invasive species. This makes the process less like looking for a needle in a haystack, and more like finding the millions of needles right under your nose.