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- Define the term biogeography and the abiotic factors that impact it
- Discuss how abiotic factors affect species distribution
Biogeography is the study of the geographic distribution of living things and the abiotic factors that affect their distribution. Abiotic factors such as temperature and rainfall vary based mainly on latitude and elevation. As these abiotic factors change, the composition of plant and animal communities also changes. For example, if you were to begin a journey at the equator and walk north, you would notice gradual changes in plant communities. At the beginning of your journey, you would see tropical wet forests with broad-leaved evergreen trees, which are characteristic of plant communities found near the equator. As you continued to travel north, you would see these broad-leaved evergreen plants eventually give rise to seasonally dry forests with scattered trees. You would also begin to notice changes in temperature and moisture. At about 30 degrees north, these forests would give way to deserts, which are characterized by low precipitation.
Moving farther north, you would see that deserts are replaced by grasslands or prairies. Eventually, grasslands are replaced by deciduous temperate forests. These deciduous forests give way to the boreal forests found in the subarctic, the area south of the Arctic Circle. Finally, you would reach the Arctic tundra, which is found at the most northern latitudes. This trek north reveals gradual changes in both climate and the types of organisms that have adapted to environmental factors associated with ecosystems found at different latitudes. However, different ecosystems exist at the same latitude due in part to abiotic factors such as jet streams, the Gulf Stream, and ocean currents. If you were to hike up a mountain, the changes you would see in the vegetation would parallel those as you move to higher latitudes.
Ecologists who study biogeography examine patterns of species distribution. No species exists everywhere; for example, the Venus flytrap is endemic to a small area in North and South Carolina. An endemic species is one which is naturally found only in a specific geographic area that is usually restricted in size. Other species are generalists: species which live in a wide variety of geographic areas; the raccoon, for example, is native to most of North and Central America.
Species distribution patterns are based on biotic and abiotic factors and their influences during the very long periods of time required for species evolution; therefore, early studies of biogeography were closely linked to the emergence of evolutionary thinking in the eighteenth century. Some of the most distinctive assemblages of plants and animals occur in regions that have been physically separated for millions of years by geographic barriers. Biologists estimate that Australia, for example, has between 600,000 and 700,000 species of plants and animals. Approximately 3/4 of living plant and mammal species are endemic species found solely in Australia (Figure 1).
Sometimes ecologists discover unique patterns of species distribution by determining where species are not found. Hawaii, for example, has no native land species of reptiles or amphibians, and has only one native terrestrial mammal, the hoary bat. Most of New Guinea, as another example, lacks placental mammals.
Check out this video to observe a platypus swimming in its natural habitat in New South Wales, Australia. Note that this video has no narration.
A video element has been excluded from this version of the text. You can watch it online here: pb.libretexts.org/fob1/?p=516
Plants can be endemic or generalists: endemic plants are found only on specific regions of the Earth, while generalists are found on many regions. Isolated land masses—such as Australia, Hawaii, and Madagascar—often have large numbers of endemic plant species. Some of these plants are endangered due to human activity. The forest gardenia (Gardenia brighamii), for instance, is endemic to Hawaii; only an estimated 15–20 trees are thought to exist.
What is biogeography?
Biogeography is known as the branch of biology focused on the study of the distribution of living beings in a geographic space . It can also be considered as a specialization of geography that is oriented to the places that living organisms occupy on Earth .
Biogeography combines concepts, tools and techniques from zoology , botany and ecology , among other areas of knowledge. Its object of study is the distribution of species on the planet, dedicating itself to analyzing its origin and the changes that are registered in it.
The biological evolution , the climate change and changes in the structure of the oceans and continents by continental drift and orogénesis are factors affecting the geographical distribution of living beings and, therefore, part of the interests of biogeography.
The concept of continental drift , mentioned in the previous paragraph, refers to the movement of the continental masses in relation to the others. This is a hypothesis developed by a German-born geophysicist and meteorologist in 1912 based on various observations. It is worth mentioning that about fifty years passed before this phenomenon could be adequately explained, thanks to the advances made in the field of plate tectonics , the theory that defines the structure of the most rigid and coldest part of our planet.
The orogénesis , meanwhile, is the process through which the earth ‘s crust and loses extension is bent at a portion elongated arising as a result of a thrust. In general, this phenomenon is accompanied by bending and thrust, that is, deformations and failures. In this context we speak of orogens to give name to the mountain ranges, whose creation takes place when a tectonic plate is subjected to a pressure that pushes it towards the surface.
Because the terrestrial conditions are very different according to the place, the biogeography must study each system in particular, since two evolutions never occur in the same way. Nor are there general precepts that allow, through deduction, to generate knowledge about the various modes of distribution of living organisms on the earth’s surface.
In this context, it is common to distinguish between historical biogeography and ecological biogeography. The historical biogeography studies the changes in the distribution of species in time , while the ecological biogeography emphasizes both temporary and space changes.
It is known by the name of biogeographic or distribution area to the geographic space in which the distribution of species and subspecies takes place. Within biogeography there is an auxiliary science, a specialty, called chorology , which focuses on the study of the distribution area of living beings.
As can be deduced, this field is of great importance for the development of human knowledge, since we are characterized by the thirst for knowledge about everything that surrounds us. Among the issues that are related to the biogeographic area we can highlight demography , the science in charge of studying human populations and their different properties, as well as the possibilities that different taxa have to survive.
On the other hand, there is conservation biology , the science that, since the 1980s, has studied the causes of the marked decline in biodiversity in all its layers, ranging from genetics to ecosystems. One of the main objectives of this scientific discipline is to find a way to reduce this loss to a minimum.
ISLAND BIOGEOGRAPHY AND EVOLUTION: SOLVING A PHYLOGENETIC PUZZLE USING MOLECULAR GENETICS
The strength of the activity is its depth and interdisciplinary approach. This activity reinforces the interdisciplinary nature of modern science. Students utilize real data from real scientists. Students apply the principles of evolution in their reasoning to make use of this data from geology and biological science. This activity originated at Princeton University in the summer of 1995 while I was a participant in the Woodrow Wilson National Foundation Institute on Biology. Though now modified, it was written as part of a biology module on evolution called “Evolution: A Context for Biology.” My original intent was to write a similar activity on Galapagos Finches, but that proved to be too complex and DNA mapping data had yet to be published.
For purposes of this publication, I have placed the student activity in the beginning followed by teacher information and my discussion of possible solutions.
ISLAND BIOGEOGRAPHY AND EVOLUTION: SOLVING A PHYLOGENETIC PUZZLE WITH MOLECULAR GENETICS
Background Figure 1 (left) illustrates one of the many populations of lizards living on the Canary Islands. The Canary Islands form an archipelago of seven volcanic islands just west of the African continent (Map 1). The island chain starts about 85 km (50 miles) west of the continent, following a fault line of the Atlas Mountains in northern Africa. Geologists theorize that a geologic hot spot of upwelling magma has been drifting westward for the past 20 million years, gradually forming the islands as it moves. Thus the most eastern island, Lanzarote, is oldest, while the smaller western island, Hierro, is the youngest, about 0.8 million years old. Volcanic islands are particularly good laboratories for evolutionary science because they can be dated accurately using radioactive isotope decay and because they start out as lifeless masses of rock emerging from the sea.
The development of ecosystems on volcanic islands is somewhat unpredictable. However, ecological succession does occur first with pioneer organisms that gradually alter the environment until a stable climax community is established. What is unpredictable is what plant and animal species will colonize these new environments. Much of this is left to climate, proximity to other land masses, and of course, chance. This investigation deals with three species of lizards of the genus Gallotia, and within one of these species, Gallotia galloti, four separate island populations. The arrival of the Gallotia lizards was probably by rafting (See Map 1). Rafts of natural vegetation are often washed out to sea when high river levels cause river banks to collapse, carrying away both plants and clinging animals. Oceanic currents in this region vary with the seasons. Colonization by airborne organisms, such as insects and birds, usually occurs during storms. In any case, there are some general principles of island colonization:
1) The closer the island to another land mass, the higher the probability of colonization.
2) The older the island, the more likely it will be colonized.
3) The larger the island, the more species are likely to be established.
4) Geographic isolation reduces gene flow between populations.
5) Over time, colonial populations become genetically divergent from their parent population due to natural selection, mutation, and/or genetic drift.
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Problem Evolution biologists have been faced with an interesting problem. What is the phylogenetic history of the three species and seven populations of Gallotia lizards on the Canary Islands? Does the presence of four morphologically different populations of G. galloti on the four westernmost islands (Map 2) imply continuing evolution? In this investigation, you will use data from geography, geological history, morphology (body size), and molecular genetics to develop answers to these questions.
1) Which island is most likely to have been colonized first and which last? Tell why you think so.
2) Using Map 2 (download a pdf version—includes Table 1 below) and your geographic reasoning, draw on a separate page a hypothetical phylogenetic (family) tree of the three species and the three additional populations of G. galloti. Your teacher will demonstrate how to draw a phylogenetic tree. Label your end branches with the following population names:
Table 1. Maximum age of the Canary Islands in millions of years. (Anguita et al., 1986)
|Lanzarote & |
1) Explain how the data in Table 1 (above) support your phylogeny diagram? Or what changes should you make and why?
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Compare your two phylogeny charts. Describe how they are different.
Thorpe and his colleagues used restriction enzymes to cut the DNA, and gel electrophoresis to separate the fragments. Radioisotope tagging eventually led to the sequencing of the samples of DNA for each of the seven populations. Thorpe tested two populations on Tenerife to see if ecological differences were part of the story. He felt that because Tenerife is moist and lush in the north while arid and barren in the south, populations on that island might have some genetic differences. Also, he wondered if Tenerife was supplying colonizing lizards from two different directions. The results for Thorpe’s tests appear on the last two pages of this investigation.
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Your task is to count the differences between all pairings of the seven populations and use that data to construct a final phylogenetic tree based on genetic similarities and differences.
Procedure There are 21 different pair combinations possible using seven populations. You should work in a team of four. Each person will be responsible for counting all of the base differences for five of the 21 pairs (see chart below). The pairings are listed on Table 2 (download a pdf version). Note that the first pairing has been counted for you. Record your results in Table 2. When all teams are done, the data will be checked for agreement. The easiest way to make accurate counts is to cut the paper into four strips and tape them end to end in the correct order, A to D. You will then compare pairs of strips side by side to count the differences.
There are 21 possible pairings, each team member selects five pairings other than 1/2.
|Student #1||Student #2||Student #3||Student #4|
INTERPRETATIONS AND CONCLUSIONS
Low numbers express more genetic similarity and imply more recent common ancestry. Pairs with high numbers are said to have greater genetic distance between them. In other words, large numbers imply they are less genetically alike, have more distant ancestry, and have been separated longer. On a phylogenetic tree, early ancestry is expressed by low branches while more recently evolved are on the higher branches. Branches that are far apart imply greater genetic distance.
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1) In Table 2, large numbers imply that pairs of populations are less related. Why is this?
2) Among the six populations, there are three species. How many base pair differences is the minimum to separate any two species of these lizards? (Remember, don’t confuse populations with species.) Give an example to support your answer.
3) Which two populations are most closely related? Justify your answer.
4) Why should you expect the populations S. Tenerife (ST) and N. Tenerife (NT) to have fewer differences than other pairings?
5) Which population is least related to the rest? Why do you say so?
Refer to your last phylogeny chart using genetic similarities and differences found in Table 2. Compare it to the phylogeny chart you drew based on the geographic distances and geologic age of the islands.
6) What difference is there between the two phylogenies?
7) Which species, G. stehlini or G. atlantica, is the ancestor of the other? Explain your reasoning.
8) Predict what is likely to happen to the four populations of G. galloti on the four westernmost islands. State what conditions will support this prediction.
Table 3. Base-pair sequences from the mitochondrial genome for cytochrome b of Gallotia species and populations. Island codes in parentheses are P = Palma, NT = north Tenerife, ST = south Tenerife, G = gomera, and H = Hierro. Each sequence consists of four lines, e.g., 1a+1b+1c+1d is the sequence for Gallotia stehlini. (Data from Thorpe et al., 1994). Download a pdf version..
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The final activity will be to use the results from the pairings to compare the differences, and use this information to develop a final phylogeny chart. The solutions are provided below. The diagrams appear to be cladograms, but technically, they are not. Their similarity to cladograms is more related to their ease in drawing. The basic scheme is that low numbers of base pair differences imply closer evolutionary relationships. The phylogeny charts are intended to stimulate student thinking about the problems of understanding past and future evolution. There are many variations to phylogenies students can come up with, some better than others. The criteria should really be: can the solution be logically explained and justified. Only the last phylogeny based on both molecular genetics and biogeography has fewer variations and needs some serious discussion to close the subject. Finally, most questions on this assignment cannot be answered without student explanation. You should emphasize that answers may vary, but logic is required for all solutions.
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The information that follows is intended as a guide to solutions to the phylogenies based on different types of data. These are my interpretations and are by no means definitive.
At left is one possible solution (download a pdf version of all three solutions pictured here) based on geographical distance and island hopping. It does not take into account actual currents which vary over time. There can be other reasonable solutions. The idea here is to get the student thinking about the logic of the problem, not its ultimate answer. Then numbers indicate the chronological sequence.
At left is a possible solution using island distribution and morphology. In using body size, one is tempted to guess that medium lizards of Palma could have been the immediate ancestors to Gomera and the small lizards of Gomera are ancestors to the small lizards of Hierro. This could contradict the argument based on distance. Again, there is no one perfect answer. Ecologists and geneticists have debated several hypotheses for years. Numbers imply chronology.
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The solution at left uses DNA evidence from Table 2 (completed table below— or download a pdf version) to deduce genetic distance. It is considered the most reliable criterion to establish evolutionary kinship. All base pairs have an equal chance for mutation and mutation rate is relatively constant, even though evolution rate is not. Note that north and south Tenerife populations are listed as one. Either may be a source for new colonization. The real surprise here is not the evolution of the smaller forms, it is that stehlini on Gran Canaria appears to have the oldest ancestry, although atlantica is actually closer to Africa. This unexpected surprise could support the hypothesis that the Gallotia lizard ancestor is European! As an extension, have students investigate the currents along the Portugal coast.
ANSWERS TO INTERPRETATIONS AND CONCLUSIONS 1) In Table 2, large numbers imply that pairs of populations are less related. Why is this? Large numbers imply distant ancestry because the longer two populations have been separated the more opportunity there has been for mutations.
2) Among the six populations, there are three species. How many base pair differences is the minimum to separate any two species of these lizards? (Remember, don’t confuse populations with species.) Give an example to support your answer. G. galloti on S. Tenerife has just 19 base pair differences from G. atlantica.
3) Which two populations are most closely related? Justify your answer. The G. galloti populations on Gomera and Hierro must be the most closely related because there are just four base pairs that are different.
4) Why should you expect the populations S. Tenerife (ST) and N. Tenerife (NT) to have fewer differences than other pairings? The S. Tenerife and N. Tenerife are just different populations on the same island, so I would expect some gene flow to occur, thus reducing differences between them.
5) Which population is least related to the rest? Why do you say so? G. stehlini is the population least related to the rest. The evidence is that G. stehlini had more genetic differences from all others, from 36 to 49!
Refer to your last phylogeny chart using genetic similarities and differences found in Table 2. Compare it to the phylogeny chart you drew based on the geographic distances and geologic age of the islands.
6) What difference is there between the two phylogenies? The big difference is which population is oldest. The last phylogeny suggests G. stehlini, not G. atlantica, which is closest to Africa.
7) Which species, G. stehlini or G. atlantica is the ancestor of the other? Explain you reasoning. G. stehlini is the ancestor to G. atlantica because stehlini has more genetic differences from the others than atlantica. It is also possible that both came from Africa independently at different times or even from Europe.
8) Predict what is likely to happen to the gene pools of the four populations of G. galloti on the four westernmost islands. State what conditions will support this prediction. I expect that each island population will continue to evolve to be a separate species because they are geographically isolated and mutations will continue to add up until they will become reproductively isolated as well.
Thorpe, R.S., and R.P. Brown. 1989. Microgeographic variation of the colour pattern of Canary Island lizard, Gallotia galloti within the island of Tenerife: distribution, pattern and hypothesis. Biological Journal of the Linnean Society 38:303.
Thorpe, R.S., D.P. McGregor, and A.M. Cumming. 1993. Population evolution of Canary Island lizards, Gallotia galloti: four base endonuclease restriction of fragment length polymorphisms of mitochondrial DNA. Biological Journal of the Linnean Society 49:219– 227.
Thorpe, R.S., R.P. Brown, M. Day, A. Malhotra, D.P. McGregor, and W. Wuster. 1994. Testing ecological and phylogenetic hypotheses in microevolutionary studies. Pp. 189 in E.P. Eggleton and R. Vane-Wright (eds.), Phylogenetics and Ecology. Academic Press, London.
Thorpe, R.S., D.P. McGregor, A.M. Cumming, and W.C. Jordan. 1994. DNA evolution and colonization sequence of island lizards in relation to geological history. Evolution 48:230.
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Map 1 redrawn from the Journal of Volcanology and Geothermal Research 30:155: F. Anguita and F. Hernan. 1986. Geochronology of some Canarian dike swarms: contribution to the volcano- tectonic evolution of the archipelago. With the kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.
Human activities have rapidly changed the distribution of biota at an unprecedented scale (McKinney & Lockwood, 1999 ) and continue to do so. Ever increasing numbers of species are transported by humans into areas outside their natural ranges (van Kleunen et al., 2015 ), which results in profound changes of biogeographical patterns (Capinha, Essl, Seebens, Moser, & Pereira, 2015 ). These alien species impact on native biodiversity due to competition, predation and hybridization and act as vectors of pathogens and diseases dangerous to both humans and other wildlife (Hof, Araújo, Jetz, & Rahbek, 2011 ). Alien species also have major economic and social impacts that directly and indirectly affect human welfare (Kumschick et al., 2015 Vilà et al., 2011 ). Although research in biological invasions has intensified over the last decades, major taxonomic and geographical knowledge gaps still remain, and global analyses of invasion patterns are still missing for some groups of organisms. This limits a comprehensive understanding of mechanisms and patterns of invasions at large scales (Pyšek et al., 2008 Richardson & Ricciardi, 2013 ) and, in turn, prevents the implementation of sound preventive response actions.
Here, we present the recently completed Global Alien Herptile Database, a comprehensive database of alien amphibian and reptile distributions in countries, federal states and biogeographically separated islands or archipelagos worldwide. We focused on established alien species, defined as those that do not occur naturally in a region and form self-sustaining, introduced populations in that region (Blackburn et al., 2011 ). We excluded casual (i.e., not permanently established) occurrences. Our database contains the distribution of established alien amphibians and reptiles in 359 regions. In a subsequent step, we use this data set to analyse: (1) the global distribution of established alien amphibians and reptiles, (2) the flows of established alien species between their native and alien ranges, (3) the temporal dynamics of invasions during the last centuries and (4) the key drivers shaping the richness of established alien amphibian and reptile species at the global scale.
Genetic Evolution of Species | Cell Biology
The concept of ‘organic evolution’ envisages that all the living forms of today developed from a common ancestor. That is, the various life forms are related by descent, which accounts for the similarities among them. The idea of organic evo­lution was not widely accepted until 1859 when Darwin published his classic work ‘The Origin of Species’.
This work contained a large body of evidence in favour of the idea that evolution continuous and it provided an attractive hypothesis to explain the mode of evolution.
Subsequently, various concepts regarding the mechanism of evolution were developed Haldane, Fischer, Wright and several others, Information’s from diverse areas of study, such as, geology, palaeontology, taxonomy, population genetics, biochemistry, molecular genetics and others have been collated and resynthesized to understand evolution.
Present Status of Genetic Evolution of Species:
The modality of evolution of species in the plant kingdom involves a combination of pro­cesses and phenomena in nature. The processes cover all the changes inherent in the concepts of Drawin, de Vries, and lately by Stebbins.
The basic materials bringing about changes in the individual of a population, are the genes and their alterations. In fact, the random gene changes provide with basic raw materials in the evolutionary process.
Such changes may be major or minor, involving alterations in structure and numbers of genes as well as of chromosomes and chromosome segments. In short, genie and chromosomal alterations occurring at random in the individuals of a population, provide the basic materials for the evolution.
The next step in the evolutionary process at the population level, is the recombination of genes between different individuals. The random hybridization between different individuals containing different genetic changes leads to the origin of new individuals with newer gene combinations. At this step, the population may represent a heterogeneous mass of individuals containing different gene combinations.
The next step in evolution is the operation of natural selection in the struggle for existence among the heterogeneous recombination’s, for opti­mum utilization of the resources in their specific environments. Ultimately through natural selec­tion, certain individuals with altered gene com­plements occupy the environmental niche with the gradual exclusion of others.
Through cross bree­ding amongst themselves, such a population ulti­mately becomes stable with specific altered gene combinations and becomes a stable genotype.
The stable population characterized by a particular gene combination, stands apart from the parental species to which the population initially belonged. Such a stabilized population, characterizing a genotype differing in phenotype from its predecessors, is often considered as attaining an incipient species level.
Such an incipient species can even undergo intercrossing with individuals of the parental population and may lose identity.
As such, the attain­ment of a species status from the level of incipi­ent species, would require a compatibility barri­er between the new and the old populations. Without this barrier, despite phenotypic differen­ces, the identity of the new population cannot be maintained.
There is every possibility of its mer­ger with parental species through breeding in absence of barrier leading to the origin of a series of graded phenotypes. The barrier to compati­bility, essential for attaining species status, can be achieved through different means.
The method without involving any genie changes leading to compatibility barrier is migration. The migration of the new population to new environment, far removed from the original, leads to geographical isolation. Such geographical isolation enables a population to develop its own phenotypic cha­racteristic adapted to the changed environment, far removed from the original.
Such species are also termed allopatric species.
The common method, other than the migration and consequent geo­graphical isolation, is the genie changes or muta­tions leading to a barrier to fertilization.
Such barrier to fertilization between species-occupying the same geographical area, otherwise termed as sympatric species, can be achieved through sea­sonal isolation, i.e., blooming at different seasons caused by genie changes in the individual.
Not necessarily seasonal, but the barrier may be pre­sent even between two species maintaining their individuality, occupying the same habitat and blooming in the same season. The compatible barrier between the two species, original and derived, can also be due to incompatibility of germinal line, the pollens and ovule.
Such genie sterility may be manifested either in the absence of fertilization or barrier to post-fertilization embry­onic development. Such sterility barrier at the genie level is the principal factor in stabilization and as such evolution of species.
Geographical abundance distributions of coastal invertebrates: using one-dimensional ranges to test biogeographic hypotheses
It is often assumed that species generally reach their highest densities in the centre of their range and decline in abundance towards the range edges. A number of mechanisms have been proposed that could theoretically support this pattern, and several ecological theories have been developed based on the assumption that this pattern occurs in nature. However, few studies have quantified geographical patterns of species abundance throughout species ranges. This is largely because of the logistical challenges of sampling throughout the large spatial areas of most species ranges. We use intertidal invertebrates, which have relatively well defined linear ranges, to test the hypothesis that species are most abundant in the centres of their ranges.
Our sampling programme covered all or most of the ranges of twelve intertidal invertebrate species along the Pacific coast of North America, from Cabo San Lucas (Baja California, Mexico) to Shelikof Island (AK, USA).
We sampled invertebrate density at forty-two field sites using quadrat and transect methods. We used a shape fitting procedure to find idealized range shapes that best fit the sampled distributions of abundance. The idealized range shapes represented both a distribution where abundance was highest at the range centre and distributions where abundance was highest at one or both of the range edges.
Overall, this suite of species did not show the expected pattern of high abundance near the range centre. Six of the species showed patterns indicative of high densities near one of their range edges, whereas only two showed patterns with high densities near their range centres. Furthermore, nine of the twelve species had sites near the range edges in which density ranked in the top 20% of all sites.
The hypothesis that species are most abundant in the centre of their ranges cannot be generalized to this diverse suite of intertidal organisms. The diversity of distribution shapes that we found suggest that evolutionary and ecological theories that assume high abundance at range centres should be re-examined with consideration of alternative abundance distributions. We suggest that sampled geographical distributions of abundance can be combined with demographic and physical factor data taken at the same scale to test hypotheses related to the causes of range boundaries and the responses of species ranges to climatic change.
Overall, we provided clarity regarding phylogenetic relationships, biogeography, and ecological niche evolution in Diapensiaceae. A phylogenetic understanding of Diapensiaceae could be improved by increased sampling within species, as we sampled only one to three individuals per species. The resolution of questions of species monophyly may require greater sampling. Additional molecular data could also improve the phylogenetic inference of Diapensiaceae. We did not include subspecies within the family due to specimen limitations. Likewise, two recently described species, Shortia rotata (Gaddy & Nuraliev, 2017 ) and S. brevistyla (Gaddy et al., 2019 ), segregates of S. sinensis and S. galacifolia, respectively, were not included because (i) we were unable to obtain specimens for S. rotata, and (ii) S. brevistyla had not been recognized when we collected samples for this study. In addition, herbarium specimens of neither S. rotata nor S. brevistyla have been annotated as distinct from S. sinensis and S. galacifolia, respectively the digitized herbarium specimen records for S. sinensis and S. galacifolia may, thus, represent lumped entities. Therefore, S. rotata and S. brevistyla could not be included as separate species in our analyses.
Many questions remain unanswered regarding the evolution of Diapensiaceae. Scott & Day ( 1983 ) noted the low chromosome number for the family—most members of Diapensiaceae have n = 6 (2n = 12), with Galax urceolata having 2n = 12, 18, or 24 (Reynolds, 1968 )—however, chromosome numbers across the complete range of most species in Diapensiaceae are unknown, and chromosome evolution within the family has not been thoroughly investigated. Scott & Day ( 1983 ) also suggested that further attention should be paid to the factors governing range size, given that dispersal appears to be limited in the majority of taxa analyzed. Although we identified that temperature shifts may have allowed D. lapponica and D. obovata to expand their ranges, much is still unknown about the persistence of the taxa through climate oscillations. Also, the effect of climate change on the family should be investigated. For example, climate change is predicted to greatly decrease the range of G. urceolata (Gaynor et al., 2018 ), and similar analyses and projections would be useful for other species in the family. We hypothesize that other species of Diapensiaceae, given their general dependence on cool temperatures, may be similarly impacted by a rapidly changing climate.
The current distributions of species of Diapensiaceae are shaped by both climatic and biogeographic factors. Disjunctions between clades recognized as genera are most likely due to ancient vicariance events. On the basis of our inferences, the disjunction between ENA and EA in Diapensiaceae can be traced to two vicariance events—(i) Pyxidanthera versus the clade of Berneuxia, Shortia, Schizocodon, and Diapensia at 49.9 Mya (95% HPD: 44.82–53.8 Mya) and (ii) a split between Shortia galacifolia and all other Shortia species around 24.1 Mya (95% HPD: 18.33–30.16 Mya). These findings clearly provide further examples of pseudocongruence across the well-known ENA–EA disjunction. Although all species of the family occupy generally similar habitats, as seen by analysis of specific ecological variables as well as ecological niche models, niche shifts have accompanied some divergences, such as the origin of Schizocodon and, more recently, between species of Schizocodon and among EA species of Shortia. Overall, the diversification in Diapensiaceae appears to have been shaped by both large-scale biogeographic factors, such as vicariance, and divergence in ecological niche among closely related species.
17.7: Biogeography and Species Distribution - Biology
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Taxonomy, Biology, Biogeography, Evolution and Conservation of the Genus Erikssonia Trimen (Lepidoptera: Lycaenidae)
A.J. Gardiner, 1,* R.F. Terblanche 2
1 1Organization for Tropical Studies, School of Animal Plant and Environmental Sciences, University of
2 2School of Environmental Sciences and Development, North-West University, Potchefstroom Campus, Priv
Biogeography: Polar Bears and Penguins
Polar bears live in the Arctic, but not the Antarctic. For penguins, the picture is reversed. The pattern of organisms around the globe -- the absence of some species from environments that would suit them, and closer relationships between species that are geographically near each other than between species that inhabit similar environments -- is persuasive evidence of the evolutionary origin of biodiversity.
Credits: Courtesy of Animation Factory and STARLab Very Low Frequency Research Group
Evidence for Evolution
Darwin, Wallace and the other 19th century naturalists who traveled widely were fascinated by the distribution of animals and plants in their habitats around the world. Why do the Galapagos Islands of South America and the Cape Verde Islands off Africa have strikingly different fauna and flora, despite having similar environments? Why does the Arctic have polar bears and Antarctica penguins?
These patterns impressed Darwin deeply. To him, they argued that species arose in single centers by descent with modification from existing species, and that their geographic range was limited by their ability to migrate to other suitable environments.
The distribution of flora and fauna of the oceanic islands provided Darwin with some of his strongest arguments. The islands contain a small number of species because immigration from the mainland was difficult, he said. Some categories of life are absent altogether, such as batrachians -- frogs, toads, and newts -- even though they would seem to be adapted for such habitats. The reason? They are killed by saltwater, so could not reach the islands by migration. Terrestrial mammals aren't found on oceanic islands more than 300 miles from the mainland. But bats, with their long-distance flying ability, are plentiful.
Another point: Most of the species on islands, while distinct from other species, are most closely related to species on the nearest mainland. Therefore, Darwin said, the island inhabitants must have migrated from the original, mainland area where the species originated. That explains why the species on the Galapagos Islands most closely resemble those on the nearby South American mainland, and those in the Cape Verdes resemble those of west Africa.
Aside from the islands, Darwin was intrigued by unusual distributions of animals and plants across the continents. He concluded that changes in locations of climatic zones over time -- the advance and retreat of glaciers, for example -- could explain some of the patterns in animals' habitats.
Just as intriguing to Darwin, and even more apparent now, is the fact that fossils of possible ancestors of living species are often found in the same parts of the globe where their descendants live today. Darwin observed this in the South American fossils he collected, relatives of today's capybaras and armadillos. Apes today live only in Africa and Asia, and that is where the fossils most resembling modern apes are also found. There are no apes, fossil or living, known from anywhere in the Americas.
These same patterns are just as impressive today. And since Darwin's day, advances in scientific understanding have shown how accurate his conclusions were. For example, plate tectonics, undreamed of when Darwin was forming his ideas, fits elegantly into Darwin's theory as another major influence on dispersal, helping to produce the patterns in the distribution of both fossils and living organisms seen around the world in modern times.