Island

An island, or an isle if you prefer the more archaic, is a simple concept: a parcel of land, distinct from the sprawling continents, utterly embraced by water. It’s not some abstract notion; it’s a tangible reality, carved by geological forces or, sometimes, by the careless hands of man.

There are the continental islands, the cast-offs of larger landmasses, sundered by the relentless grind of plate tectonics. Then there are the oceanic islands, born of fire from volcanic activity, or slowly built by the patient, calcified labor of coral reefs, eventually forming atolls. Some are mere accumulations of sediment, clinging precariously to shorelines, morphing into what we call barrier islands. Even rivers, those arteries of the land, can spawn their own miniature worlds – river islands – sculpted from debris and silt. And, of course, there are the artificial islands, human contrivances, from humble outcroppings built in lagoons to ambitious land reclamation projects that reshape coastlines for our convenience.

These isolated ecosystems, whether born of ancient geological dramas or modern engineering feats, are often cradles of unique life. Oceanic islands, by their very nature, present a formidable barrier to the outside world. This isolation forces the species that manage to arrive to evolve in solitude, their destinies shaped by the strictures of their confined environments. Continental islands, on the other hand, share a biological heritage with the landmass from which they were cleaved. The longer they have been separated, the more pronounced the divergence, a testament to the power of natural selection acting upon distinct evolutionary paths.

Humans, bless their restless souls, have been drawn to these watery enclaves for millennia. Some islands were accessible via now-vanished land bridges, others were simply fragments of continents that became detached. In the starker reaches of the north and south, seasonal or glacial ice has, at times, offered a temporary, precarious connection. Today, a surprising portion of humanity, up to ten percent, calls islands home. They are magnets for tourism, their perceived beauty, their isolation, and their distinct cultures drawing in those seeking escape or novelty.

The history of islands is also inextricably linked with colonization. European powers, in their insatiable quest for dominion, laid claim to vast swathes of the Pacific, imposing their will and their systems. While decolonization has led to the emergence of some self-governing island nations, the scars of this era remain – the lingering effects of industrialisation, the ecological disruption caused by invasive species, the grim legacy of nuclear weapons testing, and the complex, often double-edged sword of tourism. And now, the very existence of many islands is threatened by the inexorable march of climate change. Sea level rise looms like a slow-motion apocalypse for nations like the Maldives, the Marshall Islands, and Tuvalu, while the increasing ferocity of tropical cyclones wreaks havoc on infrastructure and delicate habitats. Species confined to these isolated realms are particularly vulnerable to extinction, their futures hanging by a thread.

Definition

An island, simply put, is a landmass entirely surrounded by water, set apart from the vastness of a continent. There’s a certain… ambiguity, isn't there? No universally agreed-upon size dictates the boundary between island and continent. Continents are defined by geology, by their anchoring to specific tectonic plates – the colossal building blocks of our planet. Islands, however, can be found in any watery expanse: the placid surface of a lake, the flowing currents of a river, or the boundless reach of a sea. Areas of land that vanish beneath the waves at high tide, those mere low-tide elevations, are generally not considered islands. And what of islands artificially connected to the mainland? Sometimes they are deemed "de-islanded," but the label isn't always so neat, is it? It’s a matter of perspective, I suppose.

Etymology

The word "island" itself carries a history, a linguistic ghost. It stems from the Middle English iland, itself a descendant of the Old English igland. The ig or ieg component meant 'island' when standing alone, and the -land suffix, well, that’s self-explanatory. Interestingly, the Old English ieg shares a kinship with the Swedish ö and the German Aue, and even, with a stretch, the Latin aqua – water.

The spelling, however, is a curious thing. In the 15th century, a "false etymology" took hold, influenced by the Old French word isle, which traced back to the Latin insula. This association, though mistaken, added the silent 's' to the word "island," a phonetic and etymological phantom that persists to this day. It’s almost poetic, isn't it? A word for something so grounded, yet with a whisper of the artificial in its very construction.

Geology

The genesis of islands is a story etched in the very fabric of the Earth. Many islands are found clustered in archipelagos, island chains that speak of geological processes at work beneath the surface. These chains often owe their existence to volcanic hotspots, where plumes of molten rock rise from the mantle, piercing the lithosphere. [9][10] The erupting lava builds up, forming the rocky foundations of these new lands. [9] In some cases, the slow, inexorable movement of tectonic plates across a stationary hotspot paints a linear picture of island formation. The islands furthest from the hotspot are the oldest, gradually succumbing to erosion and the embrace of the sea, while the youngest, closest to the source, remain volcanically active. The Hawaiian Islands are a prime example of this phenomenon, a chain stretching across the Pacific Ocean, with islands ranging in age from the nascent Hawaii to its ancient, eroded predecessors. [11][10] Yet, not all chains are born of this singular hotspot. Some are forged simultaneously, born from fractures in the tectonic plates themselves, creating multiple islands in a single, dramatic event. The Line Islands, all estimated to be around 8 million years old, offer evidence for this alternative formation. [10]

Other islands bear witness to the grand, slow separation of continents. The Japanese archipelago, for instance, may have been wrenched away from Eurasia by the relentless force of seafloor spreading, a process where new oceanic crust emerges, pushing the older crust apart. [10] Islands that rest upon the continental shelf are aptly termed continental islands. [3] And then there are those islands, like the remnants of New Zealand, that are all that remain of continents that have since shrunk and submerged, their once-vast surfaces now largely claimed by the ocean. It's estimated that Zealandia, the continent-like crustal fragment upon which New Zealand sits, has lost a staggering 93% of its original area to the sea. [12]

Islands can also emerge from the patient work of marine organisms. Coral reefs, built layer by painstaking layer, can grow upon submerged volcanic islands. As these reefs encircle a central lagoon, they form what we call atolls. [14] The accumulation of sediment in shallow waters also plays a role, and sometimes, tectonic uplift can raise a reef just enough for sediment to gather, giving birth to a new island. [13] Along coastlines, the ceaseless action of waves can deposit sediment, creating long, sandy ribbons known as barrier islands. These dynamic landforms are constantly shifting, eroded and rebuilt by the wind and water, acting as natural buffers against the fury of severe weather, absorbing the energy of incoming waves before they reach the shore. [15]

Even in the frozen north, islands can be tethered to the mainland by the ephemeral embrace of seasonal or glacial ice. Ross Island in Antarctica stands as an example of this frozen connection.

Formation in freshwater

Within the flowing arteries of rivers, fluvial islands emerge from the interplay of erosion and sedimentation. [16] These are often temporary, their existence dictated by the river's mood – its flow speed, water level, and the very content of its silt. [16] Yet, permanent river islands do exist, some of them quite substantial. The Bananal Island in Brazil's Tocantins River, for instance, stretches to a remarkable width of 55 kilometers, a testament to the river's enduring power. [17]

Lakes themselves are born from a variety of geological events – the sculpting power of glaciers, the slow dance of plate tectonics, or the fiery genesis of volcanism. [18] And within these freshwater bodies, lake islands can also form, their origins tied to the same processes that shaped the lake itself. [19]

Life on islands

The study of life on islands, a field known as insular biogeography, delves into the intricate ecological processes that unfold in these isolated realms. It’s a fascinating area, exploring how factors like evolution, extinction, and the sheer richness of species are shaped by the island environment. Islands serve as natural laboratories, offering scientists a contained model for understanding the mechanisms of natural selection. [20][21] This focus extends to island ecology, which examines the organisms and their surroundings, providing crucial insights that have enriched the broader field of ecology since the time of Charles Darwin. [21]

Endemism

• Main article: Endemism

The Galapagos penguin, a creature found nowhere else on Earth, is a prime example of endemism.

In the realm of biology, endemism describes the unique phenomenon of species or genera being found exclusively in a particular geographical region. Islands, with their watery boundaries, act as both barriers and incubators for life. They isolate terrestrial organisms from the mainland and, conversely, isolate the aquatic life that surrounds them. [21] Consequently, island ecosystems boast the highest rates of endemism globally, making them crucial reservoirs of biodiversity. [22] Protecting these hotspots of unique life is paramount, as they are often the most vulnerable to the threat of extinction. [23] Despite their high endemism, islands generally exhibit lower overall species richness – the total number of distinct species in a given area – compared to mainlands. [24] This is often linked to the species-area relationship, a principle that posits species richness is proportional to an island's size. Larger islands, with their greater resources, can simply support more life. Furthermore, larger populations tend to possess greater genetic diversity, which in turn fosters the process of speciation. [21]

Dispersal

The Seychelles fruit bat plays a vital role in seed dispersal across islands, a form of oceanic migration. [25]

For oceanic islands, those that have never been physically connected to a continent, life arrives only through extraordinary means. Animals must fly, be carried by other flying creatures, or embark on perilous journeys via "rafting events" on ocean currents – a phenomenon known as oceanic dispersal. [26] The sheer force of tropical cyclones can transport species across vast distances, acting as unwitting couriers. [27] Creatures like tortoises, capable of surviving weeks without sustenance, can endure long voyages adrift on floating debris. [28] A striking example occurred in 1995, when fifteen iguanas were swept 300 kilometers to Anguilla in the Caribbean, an island previously devoid of their kind, having survived the journey on a raft of uprooted trees. [29] Plant species, too, are thought to traverse immense oceanic distances. New Zealand and Australia, separated by 1,500 kilometers, share over 200 native plant species, a testament to the power of long-range dispersal. [26]

Continental islands, by contrast, inherit a shared biological past with their mainland counterparts, a history that continues until the moment of separation. [26] The presence of freshwater fish on an island surrounded by saltwater, for instance, strongly suggests a former connection to a continent, as these creatures cannot navigate such barriers on their own. [21] Over time, however, evolution and extinction on a continental island can lead to significant divergence from the mainland lineage. The widespread distribution of the southern beech tree across Australia, New Zealand, South America, and New Guinea, despite their current geographical separation, is a case in point. While tectonic drift from the ancient supercontinent Gondwana is a plausible explanation, theories of oceanic dispersal also offer a compelling alternative. [26]

Evolution on island groups

Adaptive radiation, a spectacular process of diversification, is a hallmark of species colonizing island archipelagos.

Species that venture onto island archipelagos often exhibit a remarkable phenomenon known as adaptive radiation. In essence, a single ancestral species, upon arriving in a new island environment, rapidly diversifies, splitting into numerous new species or subspecies, each adapted to a particular ecological niche. This often occurs when the colonists encounter a wealth of unoccupied resources or when the resources available differ significantly from those in their original habitat. These varied pressures drive evolutionary branches in different directions, allowing for novel survival strategies to emerge. [30]

The most celebrated example of this is Darwin's finches, a group of up to fifteen tanager species endemic to the Galápagos Islands. [31] These birds evolved a remarkable array of beaks, each exquisitely suited to the specific food sources available on the different islands. The large ground finch, for instance, possesses a robust bill capable of cracking seeds and consuming fruit, while the Genovesa cactus finch has a beak adapted for extracting nectar and pulp from cacti. The green warbler-finch, mimicking the foraging behavior of true warblers, specializes in hunting spiders and insects among the island's vegetation. [30] This pattern of adaptive radiation is not unique to the Galápagos; similar evolutionary explosions have occurred on islands like Hawaii and Madagascar, and indeed, in various ecosystems beyond the purely insular. [30]

The island rule

The extinct Dodo, a creature of island legend, exemplifies the phenomenon of island gigantism.

Island life often follows a peculiar evolutionary trajectory, encapsulated by Foster's rule, also known as the island rule. This principle suggests that small mammals, such as rodents, tend to evolve towards larger body sizes, a phenomenon termed island gigantism. The giant tortoises of the Seychelles are a classic, though perhaps debated, example, as their size increase may have predated or coincided with their arrival on the island. Conversely, larger animals often shrink on islands, a process known as insular dwarfism. The pygmy hippopotamus is a notable instance of this trend. [32] The proposed mechanisms behind these shifts are varied. For smaller animals, the reduced presence of predators and competitors on islands may remove the selective pressure for small size, favoring larger individuals. For larger animals, limited resources on an island might lead to intense competition, favoring smaller individuals with lower food requirements and thus a greater chance of reproductive success, especially for their young who might otherwise suffer from malnutrition. [32]

Darwin, the Galápagos, and natural selection

The very foundations of the theory of natural selection were laid by Charles Darwin through his meticulous observations of island life, particularly on the Galápagos Islands. [21] The diverse species he encountered there, including the now-famous finches, provided crucial pieces of the puzzle that would eventually lead to his groundbreaking work. [33] His voyage aboard HMS Beagle in 1835, part of a five-year circumnavigation of the globe, brought him to these remote volcanic outposts. He famously noted that "the different islands to a considerable extent are inhabited by a different set of beings." [34] It was through studying these variations, the subtle differences in beak shape among the finches, for example, that he began to grasp how organisms adapt to their environments to survive. [34] It would take more than two decades for him to fully articulate and publish these revolutionary ideas in On the Origin of Species. [35]

Humans and islands

History of exploration

• See also: Sea § Humans and the sea

A map illustrating the chronological dispersal of the Austronesian peoples.

The human story on islands stretches back to the Paleolithic era, with evidence suggesting colonization of the Indonesian islands of Flores and Timor occurred as early as 100,000 to 200,000 years ago, requiring water crossings of at least 29 kilometers. [37] Some islands, like Honshu in Japan, were likely colonized before becoming islands, through the temporary existence of land bridges. [37]

The true pioneers of long-distance oceanic island settlement were the Polynesians. [38] While earlier island migrations often involved shorter sea voyages, Polynesians ventured across distances of 2,000 to 3,200 kilometers, navigating the vast Pacific Ocean without the aid of modern navigational instruments, in search of new lands. [38][39] Their remarkable voyages, beginning between 1100 and 800 BC, saw them spread eastward from New Guinea and the Solomon Islands to populate islands like Fiji and Samoa. [40] Their migrations eventually reached the extreme eastern boundary of Polynesia at Easter Island and the southern limit at New Zealand, where the first settlements are estimated to have occurred between 1250 and 1300. [41]

Historians continue to ponder the factors that led to the settlement of some remote islands while others remained uninhabited. [37] Generally, larger islands, capable of sustaining larger populations, were more likely to be settled. Smaller islands, too resource-poor to be self-sufficient, could still be habitable if they were within a "commuting" distance of more resource-rich islands. [37] The presence of islands could be detected by observing seabirds, noticing unusual cloud formations, and tracking shifts in wave patterns. [39][38] The possibility of human extinction on islands is also evidenced by explorers finding islands with signs of past habitation but no current inhabitants. [37]

It's important to note that not all island societies maintained a connection to the sea. [37][42] The indigenous people of the Canary Islands, for example, are believed to have lost their seafaring skills over time after the islands were conquered by the Spanish Empire in 1496, having been settled since the first century AD. [42] One hypothesis suggests that with little incentive for trade and limited contact with the mainland, the need for sophisticated maritime technology diminished. [42]

The motivations behind island exploration remain a subject of debate. While some early historians proposed that island colonization was largely accidental, perhaps due to vessels being swept off course, others draw parallels between the ambitious voyages of Polynesians and explorers like Christopher Columbus, who sought new trade routes across the Atlantic Ocean. [37] These perspectives suggest that the allure of recognition and wealth spurred explorers to undertake perilous journeys, though often with limited success. [37]

Lifestyle

Approximately 10% of the global population resides on islands. [44] The study of island cultures, often referred to as island studies, is a field driven by the unique characteristics of these societies, shaped by their distinct environments and their relative isolation from mainland cultures. [44] Several factors contribute to this uniqueness: firstly, the inherent political and geographical separation from continental influences. [44] Secondly, the limited resources and specific ecological conditions often foster cultures deeply intertwined with the marine environment, emphasizing fishing and sailing. [44] Thirdly, islands frequently possess a significant and enduring historical and political importance. [44]

A breadfruit tree, a staple in Polynesian diets, is shown here in Malaysia. Cultivated taro plants, a staple food for many island cultures.

Diet

Protein for the Polynesian diet was predominantly sourced from the sea. [45] Their fishing practices ranged from near-shore activities to deep-water expeditions. It's recorded that the Rapa Nui people would venture as far as 500 kilometers from shore to fish in coral reefs. [46] A variety of methods were employed, including spear, line, and net fishing, to catch species such as tuna, sharks, and stingrays. [46] Beyond fishing, island cultures cultivated a diverse array of native and introduced crops. [42] Polynesians grew indigenous yam, taro, breadfruit, banana, and coconut, alongside other fruits and vegetables. [48] The specific agricultural focus varied with climate; for instance, the Hawaiian Islands were known for their sophisticated irrigated taro fields, [47] while in islands like Tahiti, breadfruit was more widely cultivated and often fermented for preservation. [49] Archaeological evidence suggests that the inhabitants of the Canary Islands supplemented their diet by consuming the roots of ferns, a practice that left a significant mark on their molars. [42] These islanders also cultivated barley and raised livestock, including goats. [42]

Island nations and territories

• Further information: Island country

Many island nations, despite their limited landmass and natural resources, hold sway over vast fisheries and possess significant deposits of copper, gold, and nickel, as well as oil deposits. The inherent natural beauty of these islands also makes them prime destinations for tourism. Furthermore, islands hold considerable geopolitical value, serving as strategic locations for naval bases, weapons testing, and general territorial control. French Polynesia is a notable example, receiving substantial military funding and aid from France. [50] The Palau, Federated States of Micronesia, and Marshall Islands are Pacific island nations that maintain a unique defense, aid, and immigration agreement with the United States known as a Compact of Free Association. [51]

Colonization

Residents of Bikini Atoll are shown here as they evacuated due to nuclear testing.

From the era of Western exploration onwards, island nations across the Pacific, Micronesia, and beyond became targets of colonization. [52] These islands also attracted the attention of Christian missionaries, who, despite encountering resistance, often found success by aligning with local chiefs who sought European support to consolidate their power. Beginning in the 16th century, European powers gradually brought most of Oceania under their colonial administration. [53] Pohnpei was claimed by Spain as early as 1526, subsequently passing through German and Japanese hands before becoming part of the Federated States of Micronesia in 1982, retaining a "free association" status with the U.S. [54] Guam, a former Spanish territory until 1898, is now an unincorporated territory of the U.S. [55]

The period of decolonization saw many island states achieve independence or some measure of self-governance. [56] However, the legacy of colonization is complex. Nuclear weapons testing in the Marshall Islands devastated many atolls, rendering them uninhabitable and leading to the forced displacement of populations, while also contributing to increased cancer rates due to radiation. [52] The imposition of colonial rule often resulted in a decline of traditional cultural practices. In places like Hawaii, for example, Native Hawaiians are now a minority. Cultural norms centered on communal land ownership and less individualistic decision-making may present challenges for some island cultures navigating the global capitalist economy, potentially hindering economic growth. [56]

Tourists flock to tropical beaches like this one in Malapascua, the Philippines.

Tourism

Islands have long been a cherished destination for tourism, their unique climates, vibrant cultures, and breathtaking natural beauty drawing visitors from around the globe. However, islands can face challenges related to transportation connectivity, relying heavily on airplanes and boats, and can experience strain on their infrastructure due to the influx of tourists. [57] Islands in colder climates often depend on seasonal tourism, attracting visitors interested in nature or local traditions, with tourism forming just one component of their economy. In stark contrast, tropical islands frequently derive the majority of their economic activity and shape their built environment from tourism. These islands may also require consistent foreign aid to sustain economic growth. This over-reliance can exacerbate social inequality and lead to environmental degradation. During periods of tourism downturns, these economies struggle to compensate for the lost revenue through other industries. [57]

Threats to islands

San Juan, Puerto Rico, grappling with the aftermath of Hurricane Maria. Climate change is projected to intensify inland flooding on islands. • Further information: Effects of climate change on small island countries

Climate change poses a grave and multifaceted threat to human development on islands. The specter of sea level rise, the increasing intensity of tropical cyclones, the devastating impact of coral bleaching, and the proliferation of invasive species all conspire to undermine the stability and habitability of island nations. [58] For instance, Hurricane Maria in 2017 virtually obliterated the infrastructure of Dominica. Beyond immediate destruction, sea level rise and other climatic shifts can deplete vital freshwater reserves, leading to prolonged droughts. [58] These accumulating risks threaten to render islands, particularly smaller ones, increasingly uninhabitable. The peril extends beyond human populations, endangering the unique plant and animal life that call these isolated realms home. It is estimated that nearly half of all land species facing extinction reside on islands. [58] A comprehensive 2017 review identified 1,189 highly threatened vertebrate species across 1,288 islands, accounting for 41% of the global total. [59] The escalating frequency of coral bleaching jeopardizes marine ecosystems, many of which are the very foundation of island economies. [58]

Low-lying islands face the existential threat of complete submersion as sea levels continue to rise. Tuvalu gained international attention when its leaders held a press conference partially submerged in water to highlight the dire reality of their nation sinking. [60] In response, Tuvalu forged a partnership with Australia, allowing for the annual migration of 280 of its citizens to become permanent residents there. The Marshall Islands, an archipelago comprising 1,156 islands, is another nation facing an existential threat from rising seas. [60]

The increasing intensity of tropical storms also facilitates the long-distance transport and introduction of invasive species to islands. Floodwaters from these events can carry plants further inland than they would naturally travel, introducing them to new, often vulnerable, habitats. [27] Human activities, such as agriculture and global trade, have also served as vectors for introducing non-native species to islands. These introductions can have devastating consequences for island ecosystems, which are often small and fragile. The apple snail, for example, initially introduced to the U.S. by aquarium enthusiasts, has spread via hurricanes across the Gulf Coast and into neighboring islands. [27] These invasive species compete fiercely with native wildlife for resources, and in some cases, their unchecked proliferation can displace entire native communities. [27]

Artificial islands

• Main article: Artificial island

Kansai International Airport in Osaka is a prominent example of an artificial island.

For centuries, humanity has been engaged in the creation of islands through land reclamation. [61] Early examples can be found in the Solomon Islands, where inhabitants constructed eighty islands by piling coral and rock into the Lau Lagoon. [61] Traditional methods often involved the use of a revetment, where barges would deposit sandbags or stones into the sea to raise the land level. This was followed by filling the area with sand or gravel and reinforcing it with the revetment structure. [62] Another construction technique utilizes permanent caissons, which are sealed structures, typically made of steel or concrete, that are sunk and then filled with sand. [62]

Modern artificial islands are often monumental undertakings, involving the pouring of millions of tons of sand into the ocean, as seen in projects like Pearl Island in Qatar or the ambitious Palm Islands in Dubai. [61] These islands are frequently developed for real estate development, with plots sold for private ownership or the construction of residences. [61] Even offshore oil platforms can be considered a form of artificial island. In some instances, atolls have been encased in concrete to create artificial islands for military purposes, a practice observed in the South China Sea. [61][63] These structures, built upon what were previously low-tide elevations (landmasses only exposed during low tide), may not hold the same legal status as naturally formed islands under the United Nations Convention on the Law of the Sea, potentially conferring different legal rights. [63]