The Peculiar Floras and Faunas of Oceanic Islands LLM 2 2019 The Peculiar Floras and Faunas of Oceanic Islands

NFLD. and plate tectonics.

Geology of Scotland.

The Trump administration discusses global warming.

From last week we learned that; Most oceanic islands were formed by plate tectonics. They vary in character in part because of their origins – whether they formed at spreading centres, subduction zones or at hot spots.

Bathymetry of the global ocean, volcanoes and oceanic islands.

Caribbean islands and PT

Oceanic islands offer limited opportunities to plants and animals Oceanic islands offer limited opportunities to plants and animals. The most obvious constraints are size, isolation and the natural hazards impacting on island life.

Issues common to island biota; 1. getting there 2. surviving 3. establishing a viable population. 4. adapting. . Over time this involves evolution.

All islands suffer from varying degrees of isolation All islands suffer from varying degrees of isolation. The degree of isolation will largely determine what can reach the island. New individuals may fly, swim, float (plants, some animals on vegetation rafts, etc.), be airborne (spiders, spores, etc.).

All movement requires some form of long-distance dispersal All movement requires some form of long-distance dispersal. This may be direct (sweepstake route) or staged (stepping stone route). In general, the greater the distance, the fewer are the successful immigrants and the more peculiar the biota.

Wind dispersal of pollen, seeds and spores.

Mouth of the Amazon(below). Floating vegetation mat (right) Mouth of the Amazon(below). Floating vegetation mat (right). Water hyacinth mat (below right).

There are about 40,000 sealions in the Galapagos There are about 40,000 sealions in the Galapagos. How they got there is not hard to imagine.

Leatherback turtle migration.

Blue footed boobies – common in the Galapagos, but not endemic

Migration of the sooty shearwater.

Coconut – the classic tropical traveller.

Water dispersal – red mangrove

Many tropical seeds are dispersed by water or by animals.

Because of the difficulties of access and survival, island biotas are; Disharmonic Low in species richness Highly endemic

Disharmonic biota Isolated islands usually lack many elements of biota that are familiar to us. There may be reptiles, but no amphibians, few (if any) mammals, and no freshwater fish. On many islands , the top predators are reptiles or birds.

In the Galapagos there are many species of reptiles, but no amphibians In the Galapagos there are many species of reptiles, but no amphibians. There are few terrestrial mammals (two species of bat, and once there were seven species of rice rats). In Hawaii, there are NO native reptiles or amphibians.

On remote islands, bats are often the only native mammals

The lack of certain elements is in part compensated by adaptive radiation– species evolve into new forms and functions that fill vacant niches. The famous Darwin’s finches, 13 species, are derived from a single arrival.

For Hawaii, it is thought that the 1400 native plant species, 8000 species of insect, 1000 species of land snails, 200 species of birds, etc. are derived from perhaps only 1000 visitors over 70 million years.

Hawaiian honeycreepers- at least 51 species (less than half remain)

Hawaiian fruit flies – 1000+ species, 25% of the world’s Drosophila biodiversity

Low Species Richness Low species richness and diversity is in part a function of isolation, area and the persistent threats to survival. These relationships are modelled in island biogeography theory, first proposed by MacArthur and Wilson, 1957.

Simply put, it suggests that (a) there is a relationship between the number of species and island area, and (b) that species number is a balance between immigration and extinction.

Reptiles on islands

Endemism An endemic species is one unique to a limited area (e.g. island).The degree of endemism increases with isolation and time. Adaptive radiation is the major driver. On islands, the processes are common with birds (Darwin’s finches, Hawaiian honeycreepers), insects (Hawaiian Drosophila), etc.

Global endemism

Endemicity in the Galapagos Of nearly 500 plant species, nearly 50% are endemic. Of 22 reptile species, 20 are endemic (all 3 snake species, all 7 lava lizard species, 5 species of gecko and 2 species of iguana) Of 29 land bird species, 22 are endemic. Of land snails, 80 of 83 species are endemic.

Galapagos penguin – perhaps a population of 1500, but that may be halved during a severe El Nino.

Lonesome George, the last Pinta tortoise – RIP 2012 Lonesome George, the last Pinta tortoise – RIP 2012. He was at least 180 years old.

Flightless cormorant

They may be reflected in obvious morphological differences, but may involve the evolution of flightlessness or the development of gigantism or nanism (on remote islands usually big animals become smaller and small ones get larger).

Size changes- in general, big things get smaller and small things get bigger. Why?

Weta, New Zealand – 100 species in two families

Powelliphanta, a giant carnivorous snail from New Zealand Powelliphanta, a giant carnivorous snail from New Zealand. May live to 20 years.

Komodo dragon. 150kg, carnivorous. Top predator Komodo dragon. 150kg, carnivorous. Top predator. 25-30 year life expectancy.

Pygmy rhinos from Sumatra – adults are less than 150cm tall.

Did these changes in size impact on humans Did these changes in size impact on humans? Homo floresiensis (left) discovered in 2003 on the island of Flores

low reproductive rates longevity Other adaptations include; flightlessness fearlessness low reproductive rates longevity

Kakapo, New Zealand, the world’s largest parrot – flightless, nocturnal, lives up to 120 years.

Natural Threats to Survival It should be remembered that island species are naturally at risk – from disturbances (volcanic eruptions, tsunamis, rising sea level, pathogens, etc.). Some of these are episodic, while others such as El Nino impose regular threats. Species populations are often small and may be close to Minimum Viable Population.

This concept suggests that if a naturally small population falls below a critical value it will sooner or later become extinct. The small population would be more liable to the catastrophies listed above and suffer from genetic problems.

Islands make about 5% of the Earth’s land area, but over 75% of known animal extinctions have occurred on islands.

Historical bird and mammal extinctions on islands and continents

Humans and island extinction. As with continents, most island extinctions are caused by (a) overexploitation, (b) removal of natural habitat and (c) the introduction of alien species (cats, dogs, goats, rats, etc.).

The dodo (Raphus cucullatus) From Mauritius. Flightless. Trusting. Low reproductive capacity. Plentiful and tasty fresh meat for sailors. Extinct by 1660.

Bushmeat

Feral cat with marine iguana, Galapagos.

Feral goats, Galapagos. Eliminated from some islands (Santiago, 2009).

Spread of quinine, Galapagos.

Although Europeans are usually blamed for these extinctions, it’s clear that others share the blame. The Polynesian travels across the Pacific were associated with a wave of extinction. Half the endemic bird species of Hawaii were eliminated soon after settlement. New Zealand was similarly impacted.

Hawaiian Feather Cloak – 20,000 birds!

Islands were settled late – again a reflection of isolation and opportunity. In part, this was a technological issue – the need for seaworthy boats and navigational skills. Next week we’ll take a look at how and when people colonized the Pacific.