Island Evolution

"Cynotherium sardous is a small canid that lived on the island of Sardinia-Corsica during the Pleistocene. Once on the island, the species gradually adapted, and became specialized in
hunting small prey like the lagomorph Prolagus. Moreover, in order to fulfil mass-related energetic requi rements, the species had to reduce body size compared to its ancestor Xenocyon,
which was larger than the grey wolf. Cynotherium carried its head much in the way foxes do and was able to hold its body low to the ground when stalking. In addition, it could move its head laterally better than any living canid."

Systematic study of charts, maps and satellite images pertaining to 1967-68, 1975, 1992, 1997, 2000, 2003, 2006, 2009 and 2012, indicate that the Balari Bar steadily increased, choking up the northern portion of the Haldia Channel, on the west of the Hugli Estuary. Its rapid growth, from 0.29 km^2 in 1997 to 3.83 km^2 in 2012, started to threaten the Haldia Dock Complex (HDC). Eight superimposed profiles across the 15 km Balari Reach of the estuary show gradual deterioration of the western Haldia Channel and the improvement of the eastern Rangafalla Channel resulting in the concentration of the tidal flows in the latter. The decrease in the overall capacity of the reach has been 8.13% from 2000 to 2012. The result of this is reflected on the performance of the HDC as some of its share of cargo is diverted to the other sea ports in the vicinity.

Half a century ago, MacArthur and Wilson proposed
that the number of species on islands tends
toward a dynamic equilibrium diversity around
which species richness fluctuates [1]. The current
prevailing view in island biogeography accepts
the fundamentals of MacArthur and Wilson’s theory
[2] but questions whether their prediction of
equilibrium can be fulfilled over evolutionary timescales,
given the unpredictable and ever-changing
nature of island geological and biotic features
[3–7]. Here we conduct a complete molecular
phylogenetic survey of the terrestrial bird species
from four oceanic archipelagos that make up the
diverse Macaronesian bioregion—the Azores, the
Canary Islands, Cape Verde, and Madeira [8, 9].
We estimate the times at which birds colonized
and speciated in the four archipelagos, including
many previously unsampled endemic and nonendemic
taxa and their closest continental relatives.
We develop and fit a new multi-archipelago
dynamic stochastic model to these data, explicitly
incorporating information from 91 taxa, both
extant and extinct. Remarkably, we find that all
four archipelagos have independently achieved
and maintained a dynamic equilibrium over millions
of years. Biogeographical rates are homogeneous
across archipelagos, except for the Canary
Islands, which exhibit higher speciation and colonization.
Our finding that the avian communities
of the four Macaronesian archipelagos display an
equilibrium diversity pattern indicates that a diversity
plateau may be rapidly achieved on islands
where rates of in situ radiation are low and extinction
is high. This study reveals that equilibrium
processes may be more prevalent than recently
proposed, supporting MacArthur and Wilson’s
50-year-old theory.

During the Pliocene a highly endemic vertebrate fauna evolved on Gargano Island (south-east coast of Italy), comprising others the giant soricid Deinogalerix, the giant barn owl Tyto gigantea, the giant hamster Hattomys, and the prongdeer Hoplitomeryx with five horns and sabrelike ('moschid' type) upper canines. The Hoplitomeryx skeletal material forms a heterogenous group, containing four size groups; within the size groups different morphotypes may be present. All size groups share the same typical Hoplitomeryx features. These are: one central nasal horn and a pair of pronged orbital horns, protruding canines, complete fusion of the navicocuboid with the metatarsal, distally closed metatarsal gully, a non-parallel-sided astragalus, and an elongated patella. The different size groups are equally distributed over the excavated fissures, and are therefore not to be considered chronotypes. The hypothesis of an archipelago consisting of different islands each with its own morphotype cannot be confirmed.
The situation with several co-existing morphotypes on an island is paralleled by Candiacervus (Pleistocene, Crete, Greece). Opinions about its taxonomy differ, and at present two models prevail: one genus for eight morphotypes, or alternatively, two genera for five species. The second model is based upon limb proportions only, but these are invalid taxonomic features for island endemics, as they change under influence of environmental factors that differ from the mainland. Also in Hoplitomeryx the morphotypes differ in limb proportions, but here different ancestors are unlikely, because in that case they all ancestors must have shared the typical hoplitomerycid features. The morphosphere of Hoplitomeryx is too coherent to assume two or more different ancestors, and indicates a monophyletic origin of all morphotypes.
The large variation is instead explained as an example of adaptive radiation, starting when the Miocene ancestor colonized the island. The range of empty niches promoted its radiation into several trophic types, yielding a differentiation in Hoplitomeryx. The shared lack of large mammalian predators and the limited amount of food in all niches promoted the development of secondary features in all size groups (apomorphies).

"One of the diagnostic features of the Late Pleistocene deer of Crete, Candiacervus, are its apparent shortened metapodals, just as it is for other endemic island artiodactyls, e.g. Myotragus (Balearics, Spain) and Cervus astylodon (Ryukyu Islands, (Japan). The question remained whether this shortening is already present at birth or arises during postnatal ontogeny due to a difference in relative growth speed of the different limb elements. In the latter case food quantity and/or quality may have played a crucial role in the development of the diagnostic feature, whereas in the former case a genetic basis seems more likely.
From this study it appears that the shortening of the metacarpals is already present at birth. This shortening increases further during postnatal ontogeny due to a relative slower growth speed.
In addition to relative length and proportional growth, there is also the question of changes in massivity. In general a short metapodal correlates with a higher massivity. The metapodals of Candiacervus ropalophorus are far more massive than those of the compared mainland species. This study reveals that this is the case already at birth, and increases further during following ontogeny."

Summary Cynot he rium sardous is a small canid that lived on the island of Sardinia-Corsica during the Pleistocene. Once on the island, the species gradually adapted, and became specialized in hunting small prey like the lagomorph Prolagus. Moreover, in order to fulfil mass-related ener getic requi rements, the species had to reduce body size compared to its ancestor Xenocyon, which was larger than the grey wolf. Cynotherium carried its head much in the way foxes do, and was able to hold its body low to the ground when stalking. In addition, it could move its head laterally better than any living canid. Samen vat ting Cynot he rium sardous is een kleine hond achtige, die leefde op het eiland Sardinie-Corsica gedu rende het Pleis toceen. Eenmaal op het eiland paste de soort zich aan en specialiseerde zich in het jagen op kleine prooi zoals de haasachtige Prolagus. Om aan de energiebehoeften, gere lateerd aan lichaamsgewicht, te voldoen, moest de soort kleiner worden, vergeleken met z...

Nayachar is a 48 km² tidal island situated in the inner Hugli estuary, West Bengal. From 1987, the then State Government started to pursued a plan to reclaim the island and convert it to a major chemical hub. This article first briefly traces the history of past development efforts of the island, and then goes on to show why its industrialisation should be considered as an environmentally unsound idea. The principal arguments are as follows. Nayachar is an ecologically sensitive locale where the process of land-building is continuing in distinct phases. Besides, it also plays an important role in maintaining morphological equilibrium of the estuary by absorbing tidal spillage and therefore should not be reclaimed. Like all islands of the Hugli estuary, it is inherently unstable. The estuary’s deepest parts were once located right where Nayachar has currently accreted. The low-lying island is also vulnerable to wave overwash during high-magnitude tropical storms. These types of storms are set to increase their frequency due to global warming. The warming is also likely to raise the sea level, threatening the island even more. Nayachar’s northeastern part is already under erosion for the last 40 years. The strong north-directed flood tidal currents of the estuary and its adjacent shelf would create major problem for safe disposal of toxic wastes. Finally, as per the existing regulations of the Central Government, it is illegal to make any kind of construction in Nayachar, let alone industrial agglomerations.

"In the Mediterranean two types of Plio-Pleistocene islands are recognized: continent islands like Sardinia/Corsica, and ocean-like islands like Crete and Cyprus. The origin of the fauna of the first type is a Pliocene mainland fauna, while the second type is colonized by overseas sweepstake dispersal.
In both cases there is a fast adaptation to the island environment followed by a stasis, or long-lasting equilibrium. Arrival of humans caused dramatic faunal changes on Sardinia, from the Middle Pleistocene, and on Cyprus from the Early Neolithic.
The pattern of faunal changes on islands is essentially different from the faunal evolution of Plio/Pleistocene Palearctic mainland, where many faunal turnovers took place, mainly triggered by global climatological events. These events had little impact on the faunal evolution on islands."

The interest in mammalian palaeohistology has increased dramatically in the last two decades. Starting in 1849 via descriptive approaches, it has been demonstrated that bone tissue and vascularisation types correlate with several biological variables such as ontogenetic stage, growth rate, and ecology. Mammalian bone displays a large variety of bone tissues and vascularisation patterns reaching from lamellar or parallel-fibred to fibrolamellar or woven-fibred bone, depending on taxon and individual age. Here we systematically review the knowledge and methods on mammalian bone and palaeohistology and discuss potential future research fields and techniques. We present new data on the bone microstructure of two extant marsupial species and of several extinct continental and island placental mammals. Three juvenile specimens of the dwarf island hippopotamid Hippopotamus minor from the Late Pleistocene of Cyprus show reticular to plexiform fibrolamellar bone. The island murid Mikrotia ma...

Island dwarfing is a paraphyletic adaptation across numerous mammalian genera. From mammoths to foxes, extreme body size reduction is shared by diverse organisms that migrate to an island environment. Because it largely occurs owing to ecological variables, not phylogenetic ones, skeletal characters in a dwarfed taxon compared with its ancestor may appear abnormal. As a result, allometric patterns between body size and morphological traits may differ for an island dwarf compared with its ancestor. The diminutive Late Pleistocene hominin, Homo floresiensis, displays a unique character suite that is outside of the normal range of variation for any extinct or extant hominin species. To better explain these as ecological traits due to island dwarfing, this research looks at how dwarfing on islands influences limb scaling and proportions in an organism in a similar ecological niche as H. floresiensis. Here, I analyze absolute limb lengths and static allometry of limb lengths regressed on predicted body mass of dwarfed island foxes and their nondwarfed relatives. Dwarfed island foxes have significantly smaller intercepts but steeper slopes of all limb elements regressed on predicted body mass than the mainland gray fox. These allometric alterations produce limbs in the island fox that are significantly shorter than predicted for a nondwarfed gray fox of similar body mass. In addition, the humerofemoral, intermembral, and brachial indices are significantly different. These results provide a novel model for understanding skeletal variation of island endemic forms. Unique body size and proportions of H. floresiensis are plausible as ecological adaptations and likely not examples of symplesiomorphies with Australopithecus sp. Caution should be exerted when comparing an island dwarf with a closely related species as deviations from allometric expectations may be common.

The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non-equilibrium framework generating novel predictions for emergent diversity properties of oceanic islands and archipelagos. Its publication in 2008 coincided with, and spurred on, renewed attention to the dynamics of remote islands. We review progress, both in testing the GDM's predictions and in developing and enhancing ecological–evolutionary understanding of oceanic island systems through the lens of the GDM. In particular, we focus on four main themes: (i) macroecological tests using a space-for-time rationale; (ii) extensions of theory to islands following different patterns of ontogeny; (iii) the implications of GDM dynamics for lineage diversification and trait evolution; and (iv) the potential for downscaling GDM dynamics to local-scale ecological patterns and processes within islands. We also consider the implications of the GDM for understanding patterns of non-native species diversity. We demonstrate the vitality of the field of island biogeography by identifying a range of potentially productive lines for future research.

The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non-equilibrium framework generating novel predictions for emergent diversity properties of oceanic islands and archipelagos. Its publication in 2008 coincided with, and spurred on, renewed attention to the dynamics of remote islands. We review progress, both in testing the GDM's predictions and in developing and enhancing ecological-evolutionary understanding of oceanic island systems through the lens of the GDM. In particular, we focus on four main themes: (i) macroecological tests using a space-for-time rationale; (ii) extensions of theory to islands following different patterns of ontogeny; (iii) the implications of GDM dynamics for lineage diversification and trait evolutio...

Situated on the western edge of the Ganga-Brahmaputra delta and Sundarban wetlands, the macrotidal and flood-dominated Hugli is the largest estuary of eastern India. To study supratidal evolution of its islands and margins during the 20th century, five series of maps and images—pertaining to 1904-05, 1922-32, 1942 (partial coverage), 1967-69 and 2001—were used. The available materials were georeferenced and layered for digitisation of high water line (HWL). Use of Global Positioning Survey, in differential mode, was made to collect Ground Control Points and delineation of HWL from outer islands and selected stretches of the coast.
The results show that the estuary gained 17.63 km² of supratidal area at the rate of 117 ha yr-­­¹ during 1904-05–1922-32, lost 64.66 km² at the rate of 147.04 ha yr-­­¹ during 1922-32–1967-69 and again augmented 6.49 km² at the nominal rate of 19.67 ha yr-­­¹ between 1967-69 and 2001. The inner islands of the estuary somewhat followed this trend by exhibiting ‘rapid accretion–slow erosion–slow accretion’. Response of the estuary margins and the outer islands were ‘slow erosion–rapid erosion–slow erosion’ and ‘slow accretion–slow accretion–slow erosion’ respectively. Evolution of the inner islands largely controlled the evolution of the supratidal estuary as a whole. The accretion-erosion phases of the islands situated on the tidal sand ridges probably operate on 50 to 100 year cycles. Total number of islands fluctuated between 10 and 12 during the century.
The observed patterns are conformable to the regional trend of erosion at the seafaring areas and accretion in the interior areas of the Sundarban. Within the estuary, disruption of morphological equilibrium due to marginal embanking and reworking of sediments because of oscillations in thalwegs & tidal sand ridges—all contributed to the change.

The island rule describes a graded trend in insular populations of vertebrates from gigantism in small species to dwarfism in large species. The dwarfing of large mammals on islands has been observed both in the present fauna and in the fossil record. Elephants, hippopotami, deer, and other species became dwarfed on islands scattered all over the world, from the Mediterranean Sea to Indonesia, from the Eastern to Western Pacific Ocean, from the Caribbean to Canary Islands. The most rapid and well documented cases of island dwarfing known thus far took place over thousands of years. Here, we describe a rapid example of dwarfing of a large mammal-the feral cattle of Amsterdam Island, southern Indian Ocean, which dwarfed to about three quarters of its body size in slightly more than one century. This population provides us with a rare opportunity to assess the rapidity of demographic, life history, and morphological responses of large mammals to a very isolated and ecologically simple, insular environment.

For the new exhibition in the Museum of Palaeontology and Geology of the University of Athens a skeleton of the endemic Pleistocene Cretan deer was mounted. This deer differs from all known recent and extinct mainland deer, mainly in its proportions. Measurements and comparisons confirm this observation, but are not enough to make the public realize its impact. A mounted skeleton on the contrary makes it at once clear that this deer had considerably shortened limbs, especially the metapodals, whereas the body length and the vertebral column length are rather normal. The overall impression is closer to that of an insular dwarf bovid like Myotragus than to that of a small deer such as the spotted deer (Axis axis). The first problem to be tackled was the selection of the material. Since a complete articulated skeleton has never been found, a composite had to be made. For this purpose, only bones of size class II (De Vos, 1979; Dermitzakis & De Vos, 1987) coming from one layer of one ca...

Op afgelegen eilanden ontwikkelen dieren zich anders. Soms worden ze groter, soms kleiner dan soortgelijke dieren op het vaste land. Dat heeft alles te maken met de uitzonderlijke condities op de eilanden. Dieren die zich het best weten aan te passen aan een dergelijke omgeving, overleven. De aanpassing leidt vaak tot nieuwe varianten. Zo kennen we de miniolifanten, minineushoorn, de kleine vos en de kleine mens op Flores. Dit boek laat zien hoe nieuwe varianten of zelfs nieuwe soorten op de eilanden ontstaan. Ontdek de verdwenen wereld van de reuzenratten, vijfhoornige herten en miniatuurolifanten en lees de spannende verhalen over hun ontdekkingen! https://www.veenmedia.nl/nl/online-bestellen/hoe-dieren-op-eilanden-evolueren/945151014/kopen.html

Aim  Our goals here are to: (1) assess the generality of one aspect of the island rule – the progressive trend towards decrease in size in larger species – for fossil carnivores on islands; (2) offer causal explanations for this pattern and deviations from it – as far as fossil carnivores are concerned; and (3) estimate the speed of this trend.Location  Oceanic and oceanic-like islands world-wide.Methods  Body size estimates of fossil insular carnivores and of their phylogenetically closest mainland relative were obtained from our own data and the published literature. Our dataset consisted of 18 species from nine islands world-wide. These data were used to test whether the body size of fossil insular carnivores varies as a function of body size of the mainland species in combination with characteristics of the island ecosystem.Results  Dwarfism was observed in two canid species. Moderate decrease in body mass was observed in one hyena species. Gigantism was observed in one otter species. Moderate body mass increase was observed in two otter species, one galictine mustelid and perhaps one canid. Negligible or no change in body mass at all was observed in five otter species, three galictine mustelids and one genet. Size changes in teeth do not lag behind in comparison to skeletal elements in the dwarfed canids. The evolutionary speed of dwarfism in a canid lineage is low.Main conclusions  Size change in fossil terrestrial insular carnivores was constrained by certain ecological conditions, especially the availability of prey of appropriate body size. When such alternative prey was not available, the carnivores retained their mainland size. The impact of competitive carnivores seems negligible. The case of (semi-)aquatic carnivores is much less clear. The species that maintained their ancestral body mass may have changed their diet, as is evidenced by their dentition. Among the otters, one case of significant size increase was observed, perhaps best explained as being due to it entering the niche of an obligate aquatic otter. Dwarfism was not observed in otters. The island rule seems to apply to fossil carnivores, but with exceptions. The dependency of the island rule on resource availability is emphasized by the present study.

This report compares the astragalus of the endemic deer Hoplitomeryx (Gargano, Miocene) with that of a number of recent and fossil ruminants. It appears that the profile of the dorsal border deviates from the expected situation. In addition, in many astragali the axis through the cranial and the caudal half meet each other at an angle, yielding an oblique appearance. This situation resembles that of Myotragus balearicus, another endemic ruminant from the Mediterranean. A probable explanation is the decrease of muscular power needed, and the increase of stability, in relation to the convergence of the upper legs, due to a larger abdomen. Hoplitomeryx certainly was neither a runner nor a jumper.