Course:EOSC311/2021/The Influence of Plate Tectonics on New Zealand’s Biodiversity
New Zealand is known as a biodiversity hotspot[1]. The island is home to a large number of floral and fauna species that are endemic to the country thanks to its isolated nature[1][2]. Unlike many islands that are studied for their unique species, New Zealand is arguably the most interesting to analyze because the unusual way in which New Zealand has formed. The biogeographical history of this island country is closely linked to the movements of plate tectonics in the late Cretaceous time period[1]. New Zealand is a part of the larger continent of Zealandia which is almost entirely submerged into the Pacific Ocean[2][3]. In fact the islands of New Zealand and New Caledonia comprise about 6% of Zealandia and are the only portions that have re emerged since the sinking of the continent[1]. The submersion of the continent is closely linked to the tectonic activity that occurred while Zealandia was rifting from the larger supercontinent of Gondwanaland; while the re emergence of New Zealand has its ties to the subsequent plate boundary activity that occurred millions of years after Zealandia sank[1]. The country of New Zealand has since become a suitable habitat for thousands of endemic species and sub species[3].
Statement of connection and why you chose it
My major was in wildlife biology and through my education I developed a strong interest in learning more about the evolution of species. Wildlife biology and the geological material taught in this course are connected though biogeography. Biogeographical researchers study the geographic distribution of biodiversity. When species move into new regions and begin to adapt to these environments, the evolution of the species begins to take place. If the new regions are separated by physical barriers, evolution can result in more sub species or endemic species. The movement of species into these new spaces is influenced by their physical landscape which is in turn influenced by plate movement. The convergence, divergence and transformation of both oceanic and continental plates results in new physical features that dictate the migration and dispersal of species into new regions.
History of Plate Tectonics and Continental Drift Theory
The theory of plate tectonics was initially postulated over 100 years ago by Alfred Wegener (1880 - 1930)[4]. Wegener received significant notoriety over his advocacy about the theory of continental displacement[5]. In 1911, he came across a scientific publication that reviewed observations of identical Permian aged terrestrial fossils in various regions within the Southern hemisphere (i.e. South America, India, Antarctica and Africa)[1][4]. Based off the information in this publication, he decided that the only way these matching organisms could be found in all these continents is if at one point these continents were all connected together[4][5]. He coined the eventual movement of continents to their current positions as “continental drift”[5].
Wegener’s theory of continental drift was well known at the time but it was also considered to be highly controversial[5]. Several factors led to the lack of popularity surrounding his theory. His evidence of continental movement was based on very recent and often dense monographs written by scientists that weren’t well known outside of German speaking Europe [4][5]. He was also not well supported by major figures in European geology and geophysics during his time and had several influential opponents[5]. Finally, the main criticism of Wegener’s idea was that he had trouble explaining exactly what mechanism caused the continents to move to their current locations[4][5]. He suggested that continents behaved like ice bergs and were essentially floating on top of the heavier ocean crusts but without an explanation for the drivers of continental movement, his theory was dismissed by geologists[4].
Wegener’s idea of continental drift regained popularity in the 1960s thanks to support from researchers around the world[4]. By the end of the of the 1960s, the Earth’s surface was mapped into a series of large and small plates. Researchers determined that the plates were like rigid bodies and moved at rates of 1cm/ y to more than 10cm/ y[4]. The plates are approximately 50km to 100km thick and slide on the warmer less rigid material of the upper mantle[6]. Tectonic activity occurs along the plate boundaries and causes the plates to move. The movement of the plates are classified as either divergent, convergent or transformative[4]. Divergent boundaries are spreading boundaries that result in the formation of new oceanic crust[4]. Hot magma seeps to the surface due to the change in pressure and cools to form new crust along the ocean floor[7]. Convergent boundaries result in two plates moving towards each other and can occur at ocean - ocean plate boundaries, ocean - continental plate boundaries or continental - continental plate boundaries[4]. Ocean - ocean convergent plates result in a subduction of the older and colder plate underneath the lighter plate. Ocean - continent convergence results in the oceanic plate subducting underneath the continental plate similar to ocean - ocean boundaries[4]. At continent - continent convergent boundaries neither plate gets subducted instead mountains form from the crumbling of rocks.[4] The third type of plate movement occurs along transform boundaries. In this situation, one plate slides past a neighbouring plate without producing or destroying the crust[4]. No new formations are created in this movement. There is still debate over what exact forces causes the tectonic activity and plate movement. Traction due to mantle convection is argued to be critical to the movement of the plates however opposers advised it is of little importance and the ridge - push and slab - pull mechanisms are more important[5]. The movement of plate tectonics has resulted drastic changes to land accessibility by means of creating physical barriers (i.e mountains, separation of continents), connection of continents (i.e Isthmus of Panama), and development of islands (i.e. Hawaii, New Zealand)[1][8].
Plate Tectonic Influence on New Zealand's Formation
New Zealand represents an interesting case of biogeography where the movement of plate tectonics has resulted in New Zealand being a highly isolated oceanic archipelago with very unique biodiversity[9]. Unlike Hawaii and the Galapagos islands which were built on top of volcanoes that emerged from oceanic crusts; New Zealand’s islands are the terrestrial parts of Zealandia which is a continental crustal fragment that has been submerged for approximately 23 million years[1][9]. Zealandia was originally a part of the larger Gondwanaland continent which also consisted of Australia, South America, Africa, the Indian Subcontinent, and Antarctica[10]. Zealandia began to rift from Gondwanaland in the late Cretaceous period due to the opening of the Tasman sea (which created a barrier of approximately 1500 km between Australia and Zealandia)[2]. As Zealandia began to rift it also began to get stretched and thinned out. This reduction in the thickness of the crust resulted in the continent losing buoyancy and subsequently sinking 2000 m - 3000 m into the Pacific Ocean, [1].
Today the continental crust of Zealandia is approximately 20 - 25km while the the continental crust beneath Australia is about 35km thick, making it far more buoyant[1]. While the submergence of Zealandia was due to continental drift the re emergence of New Zealand was due to plate boundary collision[9]. The islands lie on top of the Alpine fault which is the continental boundary of the Pacific and Indo Australian plates[2]. These two plates began abruptly colliding with each other about 26 million years ago in the late Oligocene period. The tectonic activity from this collision generated 460 km of lateral motion and 20km of uplift [1][2]. The re emergence of New Zealand because of these colliding plates resulted in a highly heterogeneous landscape[9]. There were periods of volcanism up to 13 million years ago on the the east coast of the South Island and the present day North Island. Lake Taupo in the central part of North Island is a flooded craters of a powerful volcano which last erupted in 1850[2]. More recently, the compression along the Alpine Fault created the Southern Alps on New Zealand’s South Island[1][2]. The new mountain range resulted in an extensive alpine habitat and an extreme gradient of rainfall which led to the eventual formation of large braided rivers[2]. The isolation of New Zealand has also lead to high rates of endemism[2]. At the species level about 90% of terrestrial arthropods, dicotyledons, and grasses are endemic[2]. Terrestrial birds are known for their complete or partial lack of flight[2]. The lack of larger predators like herbivores and rodents resulted in the gigantism of numerous floral and faunal biota[2]. Gigantism is associated with New Zealand birds, geckos, phasmids, beetles, ghost moths, millipedes, centipedes, flatworms, earthworms and subantarctic mega herbs[2].
Conclusion / Your Evaluation of the Connections
The connection between biodiversity and geology is that geological factors like plate tectonic activity can play a significant role in the formation of suitable habitats on Earth. For example, the heterogeneous landscapes found in many parts of the world like New Zealand are closely linked to various geological processes that took place over the course of millions of years. The types of species that then reside in these areas display unique characteristics that can be attributed to the species acclimation to its surrounding environments some of which were formed due to plate movement. In New Zealand's scenario, the isolation of the island occurred due to plate tectonic activity. First Zealandia was separated from Gondwanaland, then the colliding tectonic plates forced the islands of New Zealand to resurface. The island landmass now has a variety of landscapes and formations that've become the only suitable habitats for many species that can't be found elsewhere in the world.
References
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- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Trewick, S. A., Paterson, A. M., & Campbell, H. J. (2007). Hello New Zealand. Journal of Biogeography, 34(1): 1-6.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 Wallis, G. P. & Trewick, S. A. (2009). New Zealand phytogeography: evolution on a small continent. Molecular Ecology, 18: 3548-3580.
- ↑ 3.0 3.1 Weins, J.J. & Donoghue, M.J. (2004) .Historical biogeography, ecology and species richness. Trends in Ecology and Evolution, 19(12): doi:10.1016/j.tree.2004.09.011
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 Panchuk, K. (2019). Plate Tectonics. In K. P. Editor (Eds.), Physical Geology. (pp. 1 - 27). University of Saskatchewan.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Greene, M. T. (1984). Alfred Wegener. Social Research, 51(3): 739-761.
- ↑ Hammond, A. L. (1971). Plate Tectonics: The Geophysics of the Earth’s Surface. Science, 173 (3991): 40 -41.
- ↑ Hallam, A. (1981). Plate tectonics, biogeography and evolution. Nature, 293: 1831-1981.
- ↑ Flessa, K. W. (1980). Biological Effects of Plate Tectonics and Continental Drift. BioScience, 30(8): 518-523.
- ↑ 9.0 9.1 9.2 9.3 McDowall, R. M. (2007). Process and pattern in the biogeography of New Zealand - a global microcosm? Journal of Biogeography, 35(2): 197-212.
- ↑ Logan, H. (2001). Gondwana invaded: An address on distinctive features of managing indigenous biodiversity in protected areas of New Zealand. Journal of the Royal Society of New Zealand, 31 (4): 813 -818.