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How diverse are species in remote, isolated areas on Earth?


If we consider land areas that have been largely isolated from each other from a human point of view, but with a similar climate - for example, a part of Europe and a part of Americas with a similar climate before the time of Columbus - generally how different can one expect the flora and fauna to be between the places?

I realize there can be quite different approaches to measuring the biological differences. Not being a biologist, I probably miss some quite important metrics. Some ideas that come to my mind:

  • How distinct are the species in each environment? For example, can we expect to see the same ant species? Same grass species? Same bacteria?
  • DNA difference based approaches: How much of the DNA material in each environment does not exist in the other one? How large a proportion of organisms in one environment does not have a close relative on the other, given some threshold closeness value?
  • Historical approach (probably overlaps the DNA approach quite a bit): How long ago (alternatively: how many generations ago) did the common ancestor of similar organisms in each environment live? Do the organisms share this number, i.e. is the common ancestor of, say, humans in Europe and America as ancient as that of ants and grasses?

The concept that you hint at, has been studied at the example of the island of Australia, where marsupials often look quite similar as their counterparts in the same ecological niche, which live outside Australia and have a placenta, and are less related on the DNA level (e.g.: squirrel-like animals, wolf-like, and the now everywhere extinct saber-toothed tiger-like… ).

If you are interested to learn more, I would highly recommend to read Jerry Coyne's "Why evolution is True" ( http://jerrycoyne.uchicago.edu/index.html )

The specific example of Europe and Americas (which does not fully capture the complexity of your question), also is quite interesting - although it is very short on an evolutionary time-scale. E.g.: American squirrels, which lack predators in Europe, and only arrived in Europe because of human journeys following the rediscovery of Americas, are partially outcompeting the beloved red squirrels ( https://en.wikipedia.org/wiki/Eastern_grey_squirrels_in_Europe )


Endemic species

Endemic species are plants and animals that exist only in one geographic region. Species can be endemic to large or small areas of the earth: some are endemic to a particular continent, some to part of a continent, and others to a single island. Usually an area that contains endemic species is isolated in some way, so that species have difficulty spreading to other areas, or it has unusual environmental characteristics to which endemic species are uniquely adapted. Endemism, or the occurrence of endemic animals and plants, is more common in some regions than in others. In isolated environments such as the Hawaiian Islands , Australia , and the southern tip of Africa, as many of 90% of naturally occurring species are endemic. In less isolated regions, including Europe and much of North America, the%age of endemic species can be very small.

Biologists who study endemism do not only consider species, the narrowest classification of living things they also look at higher level classifications of genus, family, and order. These hierarchical classifications are nested so that, in most cases, an order of plants or animals contains a number of families, each of these families includes several genera (plural of "genus"), and each genus has a number of species. These levels of classification are known as "taxonomic" levels.

Species is the narrowest taxonomic classification, with each species closely adapted to its particular environment . Therefore species are often endemic to small areas and local environmental conditions. Genera, a broader class, are usually endemic to larger regions. Families and orders more often spread across continents. As an example, the order Rodentia, or rodents, occurs throughout the world. Within this order, the family Heteromyidae occurs only in western North America and the northern edge of South America. One member of this family, the genus Dipodomys, or kangaroo rats, is restricted to several western states and part of Mexico. Finally, the species Dipodomys ingens, occurs only in a small portion of the California coast. Most often endemism is considered on the lowest taxonomic levels of genus and species.

Animals and plants can become endemic in two general ways. Some evolve in a particular place, adapting to the local environment and continuing to live within the confines of that environment. This type of endemism is known as "autochthonous," or native to the place where it is found. An "allochthonous" endemic species, by contrast, originated somewhere else but has lost most of its earlier geographic range. A familiar autochthonous endemic species is the Australian koala, which evolved in its current environment and continues to occur nowhere else. A well-known example of allochthonous endemism is the California coast redwood (Sequoia sempervirens ), which millions of years ago ranged across North America and Eurasia, but today exists only in isolated patches near the coast of northern California. Another simpler term for allochthonous endemics is "relict," meaning something that is left behind.

In addition to geographic relicts, plants or animals that have greatly restricted ranges today, there are what is known as "taxonomic relicts." These are species or genera that are sole survivors of once-diverse families or orders. Elephants are taxonomic relicts: millions of years ago the family Elephantidae had 25 different species (including woolly mammoths) in five genera. Today only two species remain, one living in Africa (Loxodonta africana ) and the other in Asia (Elephas maximus ). Horses are another familiar species whose family once had many more branches. Ten million years ago North America alone had at least 10 genera of horses. Today only a few Eurasian and African species remain, including the zebra and the ass. Common horses, all members of the species Equus caballus, returned to the New World only with the arrival of Spanish conquistadors.

Taxonomic relicts are often simultaneously geographic relicts. The ginkgo tree, for example was one of many related species that ranged across Asia 100 million years ago. Today the family Ginkgoales contains only one genus, Ginkgo, with a single species, Ginkgo biloba, that occurs naturally in only a small portion of eastern China. Similarly the coelacanth, a rare fish found only in deep waters of the Indian Ocean near Madagascar , is the sole remnant of a large and widespread group that flourished hundreds of millions of years ago.

Where living things become relict endemics, some sort of environmental change is usually involved. The redwood, the elephant, the ginkgo, and the coelacanth all originated in the Mesozoic era, 245 – 65 million years ago, when the earth was much warmer and wetter than it is today. All of these species managed to survive catastrophic environmental change that occurred at the end of the Cretaceous period, changes that eliminated dinosaurs and many other terrestrial and aquatic animals and plants. The end of the Cretaceous was only one of many periods of dramatic change more recently two million years of cold ice ages and warmer interglacial periods in the Pleistocene substantially altered the distribution of the world's plants and animals. Species that survive such events to become relicts do so by adapting to new conditions or by retreating to isolated refuges where habitable environmental conditions remain.

When endemics evolve in place, isolation is a contributing factor. A species or genus that finds itself on a remote island can evolve to take advantage of local food sources or environmental conditions, or its characteristics may simply drift away from those of related species because of a lack of contact and interbreeding. Darwin's Galapagos finches, for instance, are isolated on small islands, and on each island a unique species of finch has evolved. Each finch is now endemic to the island on which it evolved. Expanses of water isolated these evolving finch species, but other sharp environmental gradients can contribute to endemism, as well. The humid southern tip of Africa, an area known as the Cape region, has one of the richest plant communities in the world. A full 90% of the Cape's 18,500 plant species occur nowhere else. Separated from similar habitat for millions of years by an expanse of dry grasslands and desert , local families and genera have divided and specialized to exploit unique local niches. Endemic speciation, or the evolution of locally unique species, has also been important in Australia, where 32% of genera and 75% of species are endemic. Because of its long isolation, Australia even has family-level endemism, with 40 families and sub-families found only on Australia and a few nearby islands.

Especially high rates of endemism are found on long-isolated islands, such as St. Helena, New Caledonia, and the Hawaiian chain. St. Helena, a volcanic island near the middle of the Atlantic, has only 60 native plant species, but 50 of these exist nowhere else. Because of the island's distance from any other landmass, few plants have managed to reach or colonize St. Helena. Speciation among those that have reached the remote island has since increased the number of local species. Similarly Hawaii and its neighboring volcanic islands, colonized millions of years ago by a relatively small number of plants and animals, now has a wealth of locally-evolved species, genera, and sub-families. Today's 1,200 – 1,300 native Hawaiian plants derive from about 270 successful colonists 300 – 400 arthropods that survived the journey to these remote islands have produced over 6,000 descendent species today. Ninety-five percent of the archi pelago's native species are endemic, including all ground birds. New Caledonia, an island midway between Australia and Fiji, consists partly of continental rock, suggesting that at one time the island was attached to a larger landmass and its resident species had contact with those of the mainland. Nevertheless, because of long isolation 95% of native animals and plants are endemic to New Caledonia.

Ancient, deep lakes are like islands because they can retain a stable and isolated habitat for millions of years. Siberia's Lake Baikal and East Africa's Lake Tanganyika are two notable examples. Lake Tanganyika occupies a portion of the African Rift Valley, 0.9 mi (1.5 km) deep and perhaps 6 million years old. Fifty percent% of the lake's snail species are endemic, and most of its fish are only distantly related to the fish of nearby Lake Nyasa. Siberia's Lake Baikal, another rift valley lake, is 25 million years old and 1 mi (1.6 km) deep. Eighty-four percent of the lake's 2,700 plants and animals are endemic, including the nerpa, the world's only freshwater seal.

Because endemic animals and plants by definition have limited geographic ranges, they can be especially vulnerable to human invasion and habitat destruction. Island species are especially vulnerable because islands commonly lack large predators, and many island endemics evolved without defenses against predation. Cats, dogs, and other carnivores introduced by sailors have decimated many island endemics. The flora and fauna of Hawaii, exceptionally rich before Polynesians arrived with pigs, rats, and agriculture, were severely depleted because their range was limited and they had nowhere to retreat as human settlement advanced. Tropical rain forests, with extraordinary species diversity and high rates of endemism, are also vulnerable to human invasion. Many of the species eliminated daily in Amazonian rain forests are locally endemic, so that their entire range can be eliminated in a short time.

[Mary Ann Cunningham Ph.D. ]


Measuring biodiversity

Although examining counts of species is perhaps the most common method used to compare the biodiversity of various places, in practice biodiversity is weighted differently for different species, the reason being that some species are deemed more valuable or more interesting than others. One way this “value” or “interest” is assessed is by examining the diversity that exists above the species level, in the genera, families, orders, classes, and phyla to which species belong (see taxonomy). For example, the count of animal species that live on land is much higher than the count of those that live in the oceans because there are huge numbers of terrestrial insect species insects comprise many orders and families, and they constitute the largest class of arthropods, which themselves constitute the largest animal phylum. In contrast, there are fewer animal phyla in terrestrial environments than in the oceans. No animal phylum is restricted to the land, but brachiopods (see lamp shell), pogonophorans (see beardworm), and other animal phyla occur exclusively or predominantly in marine habitats.

Some species have no close relatives and exist alone in their genus, whereas others occur in genera made up of hundreds of species. Given this, one can ask whether it is a species belonging to the former or latter category that is more important. On one hand, a taxonomically distinct species—the only one in its genus or family, for example—may be more likely to be distinct biochemically and so be a valuable source for medicines simply because there is nothing else quite like it. On the other hand, although the only species in a genus carries more genetic novelty, a species belonging to a large genus might possess something of the evolutionary vitality that has led its genus to be so diverse.

A second way to weight species biodiversity is to recognize the unique biodiversity of those environments that contain few species but unusual ones. Dramatic examples come from extreme environments such as the summits of active Antarctic volcanoes (e.g., Mt. Erebus [see Ross Island] and Mt. Melbourne in the Ross Sea region), hot springs (e.g., Yellowstone National Park in the western United States), or deep-sea hydrothermal vents (see marine ecosystem: Organisms of the deep-sea vents). The numbers of species found in these places may be smaller than almost anywhere else, yet the species are quite distinctive. One such species is the bacterium Thermus aquaticus, found in the hot springs of Yellowstone. From this organism was isolated Taq polymerase, a heat-resistant enzyme crucial for a DNA-amplification technique widely used in research and medical diagnostics (see polymerase chain reaction).

More generally, areas differ in the biodiversity of species found only there. Species having relatively small ranges are called endemic species. On remote oceanic islands, almost all the native species are endemic. The Hawaiian Islands, for example, have about 1,000 plant species, a small number compared with those at the same latitude in continental Central America. Almost all the Hawaiian species, however, are found only there, whereas the species on continents may be much more widespread. Endemic species are much more vulnerable to human activity than are more widely distributed species, because it is easier to destroy all the habitat in a small geographic range than in a large one.

In addition to diversity among species, the concept of biodiversity includes the genetic diversity within species. One example is our own species, for we differ in a wide variety of characteristics that are partly or wholly genetically determined, including height, weight, skin and eye colour, behavioral traits, and resistance to various diseases. Likewise, genetic variety within a plant species may include the differences in individual plants that confer resistance to different diseases. For plants that are domesticated, such as rice, these differences may be of considerable economic importance, for they are the source of new disease-resistant domestic varieties.

The idea of biodiversity also encompasses the range of ecological communities that species form. A common approach to quantifying this type of diversity is to record the variety of ecological communities an area may contain. It is generally accepted that an area having, say, both forests and prairies is more diverse than one with forests alone, because each of these assemblages is expected to house different species. This conclusion, however, is indirect—i.e., it is likely based on differences in vegetation structure or appearance rather than directly on lists of species.

Forest and prairie are just two of a plethora of names applied to ecological assemblages defined in a variety of ways, methods, and terms, and many ideas exist regarding what constitutes an assemblage. Technical terms that imply different degrees to which assemblages can be divided spatially include association, habitat, ecosystem, biome, life zone, ecoregion, landscape, or biotype. There is also no agreement on the boundaries of assemblages—say, where the forest biome ends and the prairie biome begins. Nonetheless, especially when these approaches are applied globally, as with the ecoregions used by the World Wide Fund for Nature (World Wildlife Fund, WWF), they provide a useful guide to biodiversity patterns.


Islands and their biodiversity

When islands and archipelagos illustrate biodiversity, we need to understand how they operate as niches, otherwise conservation, even underwater, will be hindered.Raja Ampat in Indonesia Credit: © Shutterstock

When animals and plants colonise an island, the biodiversity of endemics relies on distance from a mainland and the area of the island itself. This means that remote islands maintain higher biodiversity in general. Even outstanding endemics such as the little dodo (the national bird, the manumea) in Samoa need to fit into a pattern.

What is of great interest is how groups of islands seem to combine their areas (Surface Area Relationships or SARs), especially with small islands in archipelagos. This is naturally called the small island effect, with a good example in the Kapingamarangi Atoll in Micronesia, to the north of Papua New Guinea where plants are significantly different from their relatives. The authors of this paper also studied biodiversity in the West Indian archipelagos and the British Isles with the results displayed within.

Because of their instability in terms of environmental conditions, extinction rates don't relate to area on small islands. Species diversity rarely stabilises where it has been thought that great storms can wipe out the entire community. The authors of a new paper today suggest that immigration is the key factor so far neglected by theorists. Ryan A. Chisholm, Tak Fung, Deepthi Chimalakonda and James P. O'Dwyer supply a thesis on the Maintenance of biodiversity on islands in the Proc. Roy Soc B.

Large islands, instead of recovering more quickly from environmental disturbance, often seem to have lower diversity despite a likely higher immigration rate. Instead of the theories noted above, niche constraints and immigration are proposed as maintaining the very high diversity sometimes achieved on small (and on large) islands.

This means that with niche diversity increasing slowly with area, niche constraints dominate on small islands while immigration dominates on big islands. Such a unified theory on island diversity needs severe testing, with mathematical models now available in both complex and simplified form. Many animal and plant groups were tested alongside a broad range of archipelago types. Key to the theory is the classic prediction. In this case the theory predicts that high immigration rate would decrease in a critical area where there is a transition between niche-structured regimes on small islands and colonization-extinction regimes on larger islands.

As an example of this prediction, birds and plants migrate to islands more easily than mammals in general. Mammals have a critical area for this transition at 20km 2 with birds at 0.78km 2 ! Also, total species richness is closely associated with niche diversity. A small island in Oceania might have a tree niche, a grassland niche, and a salty shrub niche, for example. These 3 niches would give 3 species a long term future on the island, although in reality these numbers would be much higher hopefully. Low immigration would maintain this relationship, though species would change over time.

Even general ecologies can be fitted into these new theories. With much greater immigration, critical areas would be very small with hundreds of species coexisting in a rainforest. This requires treating a mainland as simply a very big island, which seems realistic. In aquatic systems, lakes and even isolated coral reefs fit neatly into the theory, in many cases with proximity to a continental shelf a critical factor.

As far as conservation is concerned, forest fragmentation is creating tiny pieces of habitat that will function as islands. Biodiversity would naturally be lost from such entities because immigration is reduced and, secondarily, because of niche structural change, according to the theory. Species loss would be huge even if the niches remain more or less intact. The niche here is a dominant force while immigration is more dominant where larger islands are conserved.


A warning for other ecosystems

The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.

So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.

The Chagos Archipelago is home to some 800 species of fish, including rays, skates and dozens of varieties of shark. Phil Renaud/Khaled bin Sultan Living Oceans Foundation

We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.

Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.


What makes these border regions special?

RODOLFO DIRZO: This area is an ecological theater where evolution has engendered a plethora of plays. A multitude of factors – climatic conditions, topography, geological history, soil types – converge to create an amazing mosaic of ecosystems. A constellation of Northern temperate and Southern tropical lifeforms and lineages coincide with endemic species, as in few areas of the globe. This means these borderlands are a global responsibility.


Chapters 14 and 15 quiz

Difference in appearance
Distinct life form
Distinct species because song or behavior are different enough that each type breed only with individual of won species
individuals of many species exhibit limited variation in physical appearance,
Physical diversity of species lead that different human species
Humans all belong to same species though although different outward appearance

Biological species concept-defines a species as group of populations whose members have potential to interbreed in nature and produce offspring that then develop into fertile adults
Members of a biological species are united by being reproductively capable (potentially)
Members of different species do not mate with each other
Reproductive isolation prevents genetic exchanges and maintains a boundary between species
Some pairs clearly distinct species that interbreed
resulting offspring are hybrid


Habitat Fragmentation and Metapopulation, Metacommunity, and Metaecosystem Dynamics in Intermittent Rivers and Ephemeral Streams

Thibault Datry , . Albert Ruhí , in Intermittent Rivers and Ephemeral Streams , 2017

4.9.1 Introduction

Habitat fragmentation is defined as the process during which a large expanse of habitat is transformed into a number of smaller patches of smaller total area isolated from each other by a matrix of habitats unlike the original ( Fahrig, 2003 ). As a result, habitat fragmentation leads to both habitat loss and habitat disintegration, both of which affect biodiversity ( Benton et al., 2003 Fahrig, 2003 Haddad et al., 2015 ). For many species, populations scattered in space are prone to extinction ( Fahrig and Merriam, 1994 ) if the networks of patches are not sufficiently connected by dispersal ( Hanski, 1999 Bowne and Bowers, 2004 Van Dyck and Baguette, 2005 ). This connection depends on the availability of dispersing individuals and the ease with which these individuals can move across the landscape. This ease of movement is often termed “landscape connectivity” and is a central concept in conservation biology that is of paramount importance for population persistence, patterns of biodiversity, and functioning of ecosystems across landscapes ( Fahrig and Merriam, 1994 Kindlmann and Burel, 2008 ).

Landscape features and geomorphological constraints dictate where and how far individuals can move in all ecosystems thus affecting species coexistence and local community structure ( Salomon et al., 2006 Altermatt et al., 2011 ). In river systems, the dendritic structure of drainage networks results in isolated exterior branches (i.e., the headwaters) converging to form the mainstream channel ( Fagan, 2002 Carrara et al., 2012 Chapter 2.1 ). Moreover, the unidirectional downstream movement of water down river networks carries materials and promotes dispersal of individuals in the downstream direction. Therefore, landscape connectivity and its effects on populations and communities in dendritic networks require a reconsideration of the notion of patch isolation, fragmentation, and connectivity ( Fagan, 2002 ).

Ecological processes operating over multiple spatial and temporal scales determine patterns of population viability and distribution, biodiversity, and ecosystem functioning ( Loreau et al., 2003 ). Specifically, processes structuring populations, communities, and ecosystems occur both at local and large scales, whereby local-scale processes are influenced by processes occurring over much larger scales ( Hubbell, 2001 Leibold et al., 2004 Logue et al., 2011 ). These metasystem concepts (i.e., metapopulations, metacommunities, and metaecosystems) recognize that local discrete populations, communities, and ecosystems form networks connected by gene flow, dispersal, and flows of material and energy. Associated with the recent developments in spatial ecology ( Massol et al., 2011 ), this concept is highly relevant to explore how populations, communities, and ecosystems are organized in intermittent rivers and ephemeral streams (IRES). Stream systems possess several physical characteristics that differentiate them from patch-like systems such as sets of ponds, lakes, or meadows (e.g., Fagan, 2002 ). For instance, the dendritic structure of drainage networks directs the dispersal of organisms, restricting most dispersal within the stream corridors ( Tonkin et al., 2014 ). Also, the unidirectional flow of water means that passive drift dispersal travels primarily downstream. Such restrictions dictate that dispersal is mostly directional in stream systems, although overland dispersal may also contribute to species distributions across riverscapes. In IRES, the different contributions of spatial and temporal dispersal may complicate assumptions about the importance of directional dispersal for metapopulation and metacommunity dynamics. Therefore, IRES are excellent model systems in which to apply metasystem approaches ( Datry et al., 2016a ).

In this chapter, we address the effects of riverine network fragmentation by flow intermittence on metapopulation, metacommunity, and metaecosystem dynamics. Considering IRES as coupled aquatic-terrestrial systems, we explore how spatiotemporal patterns of flowing, nonflowing, and dry phases influence the local and regional processes involved in these dynamics. We first present the essential concepts of metasystem and spatial ecology and their relevance to the study of IRES. Then, we review and illustrate metapopulation, metacommunity, and metaecosystem dynamics in IRES, identifying promising research areas. We conclude with a synthesis of research gaps and an illustration of the value of metasystem concepts for the management and restoration of IRES.


Biology

Oceanic biology is extraordinarily complex because of the diversity of organisms that inhabit the seas, the wide range of environments they inhabit, and the varied and complex ways in which they interact with and contribute to essential global processes. Research in the Biology Department at WHOI encompasses a diversity of organisms, levels of biological organization, and approaches. WHOI biologists study organisms from the smallest scale (marine viruses, bacteria, and archaea) to the largest (whales). Department members address questions ranging from molecular and cellular processes to population structure and ecosystem function. Aspects of oceanic life are investigated using powerful techniques of molecular biology, biochemistry, cell biology, genomics, proteomics, sophisticated acoustic and optical methods, behavior, ocean informatics, and mathematical modeling of molecular processes and population dynamics.

WHOI biologists perform laboratory-based investigations as well as field studies in local Massachusetts and coastal New England waters and at sites around the globe (Polar Regions, Atlantic, Pacific and Indian Oceans coastal, open water, and deep sea). Special strengths in the department include the ecology and physiology of microbes bio-optical studies of phytoplankton advanced optical and acoustic techniques for zooplankton distribution and behavior the ecology, behavior, development, and genetic history of invertebrates the behavior and distribution of marine larvae fish ecology mathematical analysis and computer modeling of life history, population dynamics and physical-biological interactions toxicological and molecular biological research on pollution effects and adaptations and acoustical, anatomical and behavioral studies of marine mammals.


Taxonomy and Biological Control

GORDON GORDH , JOHN W. BEARDSLEY , in Handbook of Biological Control , 1999

Distinguishing Similar Species

Most modern taxonomists subscribe to the biological species concept in which total reproductive isolation between organisms is taken as an indication of species status. Although the concept has considerable merit, several problems are associated with implementation. For example, most taxonomists work primarily with preserved museum specimens, and reproductive isolation cannot be tested in museum preserved material. Biological control workers, with laboratory and insectary facilities available, are better equipped than most museum taxonomists to carry on reproductive isolation studies.

The confirmation of reproductive isolation through hybridization studies in some cases has led to reevaluation of the comparative morphology of sibling species, which, in turn, has elicited minor but consistent anatomical differences. Examples of hybridization studies with closely related taxa pertinent to biological control include Muscidifurax ( Kogan & Legner, 1970 ), Aphytis ( Rao & DeBach, 1969a , 1969b , 1969c ) and Trichogramma ( Nagarkatti and Nagaraja, 1977 ). It is important to emphasize that the taxonomy of the cultures and species involved must be carefully researched before taxonomic decisions are made based on hybridization work.

The extent of reproductive isolation has been shown to vary among organisms. Hybridization experiments with natural enemies for use in biological control projects often yield living samples of closely related natural enemies from geographically and ecologically diverse localities. These can provide the raw material for the basic hybridization studies needed to clarify the taxonomic status of similar entomophagous forms.

Not all organisms reproduce sexually. In so-called uniparental organisms, the biological species concept cannot be used to test reproductive isolation because males do not exist or exist at very low percentages of the offspring and may not be functional. The phenomenon of female-only species is called thelytoky by workers in biological control. Unfortunately for biological control workers, thelytoky is common among natural enemies of agricultural pests and presents an obstacle to accurate identification. In the absence of tests for reproductive isolation, morphometric analysis may provide clues to identity of closely related or morphologically nearly identical forms.

Parlatoria pergandii Comstock (chaff scale) represents a problem on citrus in Texas. Aphytis hispanicus (Mercet) and A. comperei (DeBach & Rosen) are among the natural enemies found on chaff scale. Both species are thelytokous and similar (cryptic species). Key anatomical characters used to distinguish the species overlap. However, Woolley and Browning (1987) have used principal component analysis and canonical variate analysis to distinguish between the species. These and other statistical techniques may be used by museum taxonomists when electrophoretic analysis is not possible.


When an animal or plant arrives at an island for the first time, the new environment will usually be different from the one it’s used to. As a result, a species will gradually adapt to survive or die out.

Over time, its appearance, behaviour and the way its body works might change – to become more successful at evading a predator, or more efficient at exploiting a new food source. For example, it might develop longer limbs, or lose those it no longer needs. Eventually, it may alter so much that it can no longer breed with its original species: it’s evolved into an entirely new species.

An island, especially a remote one, may be colonised by relatively few species. This allows the members of one species to exploit numerous different lifestyles, or ‘niches’ – a phenomenon called adaptive radiation. As the individual groups adapt to their different niches, they may evolve into distinct species. This is how one ancestor can eventually lead to the evolution of many new species – often looking and behaving quite different from each other.

On the isolation of an island, some plants and animals can rapidly evolve into not just one, but many new species.

Scientists call this adaptive radiation. And one of the best examples of it, anywhere in the world, is found on the Hawaiian island of Maui.

Here live numerous species of Hawaii’s rare honeycreepers.

And among those most exquisite adaptations is the shape of the bill. This is exactly what Darwin observed, at the very cradle of the idea of evolution, in the Galapagos Islands. Yet another group of finches, another group of modifications to bill form in adaptation to mode of life.

The first finches arrived on Hawaii five million years ago. They quickly radiated and adapted into five distinct lifestyles: Insect-picking gleaners, generalists, long-beaked nectar eaters, seed-lovers and parrot-beaked bark pickers.

And each of these different lifestyles has spawned multiple species. The total tally of these endemic birds once exceeded 50.