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15-‐03-‐19 Island Life Equilibrium Theory (MacArthur & Wilson 1967) Modiﬁca�ons (non-‐equilibrium) Applica�ons : Popula�on Ecology Conserva�on Biology (Chapters 13-‐14, Lomolino et al. 2010) 15-‐03-‐19 h�p://www.rosiepiter.com/clipart_illustra�ons/ tropical_scene_with_an_island_and_birds_0071-‐1012-‐0821-‐0312.html 1 MacArthur & Wilson’s Equilibrium Model Equilibrium species number on island # of species in mainland species pool 15-‐03-‐19 2 1 15-‐03-‐19 15-‐03-‐19 3 Succession & Disturbance Equilibrium concept (steady state) is rarely a�ained 15-‐03-‐19 4 2 15-‐03-‐19 Last Time (Chapter 13): "  MacArthur & Wilson (1967) Theory of Island Biogeography "  Supported to some degree, but fails to account for: –  Disturbance Time –  Succession eﬀects –  Species diﬀerences –  Species dynamics & interac�ons –  Habitat complexity (incl. shape) Equilibrium theory fails to consider these factors "  Today: –  Modiﬁca�ons to Theory –  Prac�cal applica�ons 15-‐03-‐19 "  Popula�on biology "  Conserva�on biology 5 Islands and the species that live on them are not sta�c en��es 15-‐03-‐19 h�p://en.wikipedia.org/wiki/Hawaiian_Islands 6 3 15-‐03-‐19 Whi�aker’s General Dynamic Model Includes Temporal Eﬀects 15-‐03-‐19 7 Islands Remarkable “laboratories” of evolu�on (Species are not sta�c en��es) 15-‐03-‐19 8 4 15-‐03-‐19 Island act as “ﬁlters” 15-‐03-‐19 Filters provide selec�ve pressures 9 Dispersal across “Wallace’s Line” Vagility, pagility, and resistence to dispersal all play a role 15-‐03-‐19 10 5 15-‐03-‐19 X “Everything is everywhere, but the environment selects” – Baas Beking 15-‐03-‐19 11 Dispersal consisera�ons "  Everything is not everywhere (dispersal is a challenge!) "  Islands tend to be populated by good dispersers. "  Once they get there, the rules may change (e.g. altered resources & compe��on) à “ecological release” is a term used to deﬁne this relaxa�on of selec�ve pressure. 15-‐03-‐19 12 6 15-‐03-‐19 Peculiar Island Phenomena "  Endemism "  Reduced dispersal (e.g. ﬂightless species) "  Gian�sm & Dwarﬁsm 15-‐03-‐19 13 Endemism 15-‐03-‐19 14 7 15-‐03-‐19 Endemism 15-‐03-‐19 Ini�al dispersal event 15 Subsequent radia�on MacArthur & Wilson’s model didn’t fully account for these processes Radia�on common on island archipelagoes 15-‐03-‐19 Reverse selec�on 16 8 15-‐03-‐19 Adap�ve radia�on – honeycreepers on Hawaiian Islands 15-‐03-‐19 17 Adap�ve Radia�on among Galapagos ﬁnches 15-‐03-‐19 18 9 15-‐03-‐19 Niche par��oning can be dynamic, as in this case of “character displacement” in Darwin’s ﬁnches 15-‐03-‐19 19 Perch height in Anolis lizards 15-‐03-‐19 Anolis carolinensis h�p://en.wikipedia.org/ wiki/Anolis 20 10 15-‐03-‐19 On islands with fewer species, Anolis lizards diversify their perch heights h�p://
en.wikipedia.org/ wiki/Anolis 15-‐03-‐19 h�p://en.wikipedia.org/wiki/Brown_Anole 21 Reduced Dispersal -‐ Flightless insects 15-‐03-‐19 22 11 15-‐03-‐19 Flightless birds: The ex�nct dodo once inhabited Mauri�us 15-‐03-‐19 23 h�p://en.wikipedia.org/wiki/Flightless_bird Reduced dispersal ability in island fruits Island species 15-‐03-‐19 Related mainland species 24 12 15-‐03-‐19 “S�cking to the Wreck” As with mariners shipwrecked near a coast, it would have been be�er for the good swimmers if they had been able to swim s�ll further, whereas it would have been be�er for the bad swimmers if they had not been able to swim at all and had stuck to the wreck – Darwin (1859) 15-‐03-‐19 25 Gigan�sm & Dwarﬁsm Tiny elephants … … and giant hedgehogs 15-‐03-‐19 26 13 15-‐03-‐19 Tree-‐sized sunﬂower & cactus -‐ Galapagos Giant plants 15-‐03-‐19 27 Trends toward dwarﬁsm & gigan�sm 15-‐03-‐19 28 14 15-‐03-‐19 Gigan�sm & Dwarﬁsm Does it apply to Hominins? Homo ﬂoresiensis fossil, Flores Island (< 1 m tall) 12,000 YA 15-‐03-‐19 29 General Principles: "  Island Rule – Tend towards medium size (dwarﬁsm in large species, and gigan�sm in small species) "  Bergmann’s Rule – body mass increases with la�tude. "  Cope’s Rule – Directed evolu�on (orthogenesis) towards larger body size 15-‐03-‐19 30 15 15-‐03-‐19 General model for body size evolu�on 15-‐03-‐19 31 Metapopula�on Theory "  Islands have provided “laboratories” for studying metapopula�ons (a larger popula�on comprised of patches of small popula�ons) "  These patches are prone to ex�nc�on and maintained by dispersal (remember Pokki’s vole studies in Finland?) 15-‐03-‐19 32 16 15-‐03-‐19 Example: metapopula�ons of voles & predators. Predators disperse in response to a dynamic popula�on of voles (food supply). Such “cyclical” popula�on dynamics are common in many predator-‐prey interac�ons Fig. 11.21, Metapopula�on – a group of subpopula�ons Molles & Cahll, 2008 living in separate loca�ons with ac�ve exchange 15-‐03-‐19 33 of individuals among subpopula�ons. Example of a classic popula�on study: Pokki (1981) studied ﬁeld voles on islands in Finland "  Pokki trapped animals and counted them "  Repeated this method on islands of diﬀerent sizes over several years number of inhabited islands
Island size
#
1972
1973
1974
1975
1976
1977
Average
% of
islands
inhabited
tiny (<1 ha)
40
15
12
28
16
4
16
38
medium
18
11
14
14
12
14
16
75
large
13
11
11
10
7
10
12
78
15-‐03-‐19 General conclusions: 1)  In no year did all the islands have voles 2)  Many popula�ons ex�nc�ons and recoloniza�ons occurred 3)  More ex�nc�ons occurred on �ny islands than larger islands (eﬀect of island size) Possible reasons: harsh winters and summer drought, preda�on Note eﬀect of island size 34 17 15-‐03-‐19 Applica�ons to Conserva�on Biology 15-‐03-‐19 35 Laurance & colleagues studies forest fragments in Brazil 15-‐03-‐19 Laurance et al. 1997 36 18 15-‐03-‐19 15-‐03-‐19 Laurance et al. 2011 Biological Conserva�on 144:56-‐67 37 Bird ex�nc�on pa�erns ﬁt the theory of Island Biogeography (fewer ex�nc�ons on larger islands) 15-‐03-‐19 Laurance et al. 2011 Biological Conserva�on 144:56-‐67 38 19 15-‐03-‐19 Fragmenta�on in Canada’s Boreal Forest 15-‐03-‐19 Schindler & Lee 2010 Biological Conserva�on 143:1571–1586 39 Migratory Species at Risk Rangifer tarandus caribou – woodland caribou 15-‐03-‐19 40 20 15-‐03-‐19 S = cAz 15-‐03-‐17 (Arrhenius Equa�on) Where S = Species number A = Area c = constant z = slope of log-‐log plot 41 Assessing species ex�nc�on risk Do threshholds exist? If so, what is the minimum habitat size that can support a species? 42 15-‐03-‐19 Fig. 21.24, Molles & Cahill 2008 42 21 15-‐03-‐19 Can habitat corridors provide connec�vity and reduce ex�nc�on of large, mobile animals? Wildlife “bridge” across the Trans-‐Canada Highway in Banﬀ 15-‐03-‐19 Fig. 21.16, Molles & Cahill 2008 43 22