Extinction -estimated species extinction is 100-1000X greater than speciation

1. Extinction -estimated species extinction is 100-1000X greater than speciation -genetic variation is being lost even in domesticated species such as wheat, corn, rice, chicken, cattle, and pigs Ex. 97% of vegetable varieties once cultivated are now extinct -word extinct has many nuances: • extinct -no member of the species remains alive anywhere in the world Ex. Montverde golden toad 2) locally extinct or extirpated-no longer found in an area that individuals once inhabited Ex. gray wolf occurred throughout North America but is locally extinct in many states 3) ecologically extinct -numbers of the populations are reduced to a point where its effects on other species in the community are negligible Ex. tigers

2. 7.1 Bachman’s warbler became extinct as a result of tropical deforestation in its wintering grounds 4) extinct in the wild –individuals of a species remain alive only in captivity Ex. Franklin tree is only found in cultivation 5) globally extinct –extinct in the wild throughout the world Ex. Montverde golden toad and the Franklin tree also fit this definition

3. Past rates of extinctions -diversity of species has been increasing since life first originated. This has not been a steady increase. There have been times where there were high rates of speciation followed by periods with little change or episodes of mass extinction Figure 7.2

4. 7.2 The number of families of marine organisms has been increasing over geological time

5. 7.3 During each of five episodes of natural mass extinction a large percentage of gradually increasing groups disappeared

6. Human-caused extinction—The Sixth Extinction Episode: -elimination of 74-86% megafauna (> 100 lbs) from Australia, North and South America by hunting -reduction of natural ecosystem size to make way for domestic animals -extinction rates during the past 2000 years mostly involve land vertebrates, especially birds,and mammals • Since 1600, 77 species (1.6%) of mammals and 129 species of birds (1.3%) have gone extinct with the majority of extinctions occurring over the last 150 years Table 7.1

8. Figure 7.4 Rate of extinction of birds during 25 year intervals: -rates of bird extinctions doubled after 1750 and tripled after 1850. -apparent decline in extinction rates is due to current practice of not declaring a species extinct until decades after they can no longer be found -many others are committed to extinction due to habitat destruction

9. Extinction rates will remain high in the coming century because of the large numbers of threatened species. Table 7.2 St. Helena ebony is reduced to two individuals on the cliff side of a south Atlantic Island. Will likely go extinct in wild but will persist in cultivation

11. Extinction rates on islands -islands have some of the highest extinction rates  -rates are often increased when competitors, predators, and diseases are introduced by human colonists and visitors Ex Box 7.1 with data from the Hawaiian islands on birds  -species extinction rates peak soon after humans occupy an island and then decline after the most vulnerable species are eliminated Figure 7.6

12. 7.6 Relationship between recently extinct or currently endangered bird species and length of time non-European peoples have occupied an island group

13. -islands often have large numbers of endemic species and they are particularly vulnerable to extinction -island plant species often have large percentages of endemics and many are threatened through habitat destruction Table 7.3

14. Island Biogeography The number of different species found on different islands depend on the size of the island.

15. Island Biogeography Islands are similar to isolated patches on the landscape. Ecologists now apply this concept to terrestrial habitats. The number of species established on an island represents a dynamic equilibrium between the immigration of new colonizing species and the extinction of previously established ones. Islands can serve almost as a laboratory for the study of biogeography. The biota of an island is simpler than that of a continental area, and the interactions are easier to understand. Some flying animals, such as birds and bats, are capable of reaching even very distant islands. Most land animals must rely on dispersal mechanisms like drifting on masses of debris. Although this process is likely rare, it certainly happens and has been documented for organisms like iguanas.

16. Island Biogeography Long distance dispersal in plants is much more likely. A great many plants are adapted for such dispersal. In addition, the long distance dispersal of a plant species can typically be accomplished by a single spore or seed, where in animals it typically requires a pair of organisms or a pregnant female. Some plants have developed seeds or fruits that can be carried in the sea without being harmed.

17. Island Biogeography Jared Diamond showed that, on very remote islands, the number of species may be less than that predicted by equilibrium theory. This is because of the great difficulty in dispersing to these islands. The ratio of observed species to the expected number declines with distance from New Guinea

18. Island Biogeography • Also, when a species is lost by extinction, it is more difficult to replace it by immigration than in a mainland situation. Island life is probably more hazardous than that on the mainland. For one thing, catastrophic events have more severe effects. There is typically no place to escape from hurricanes or volcanoes. • Island populations are more likely to go extinct than those on mainlands, for several reasons: Populations are: • 1. typically smaller. • have less genetic diversity = ________ effect. • not originally adapted to the island habitat.

19. Island Biogeography Islands are typically low in species richness relative to mainland areas of comparable size. Originally, this was explained by a nonequilibrium theory of island biogeography which stated that islands are less species rich because they have not had sufficient time to accumulate species by immigration. In 1963, Robert MacArthur and E.O. Wilson presented a new hypothesis to explain patterns of species richness on islands. Their equilibrium theory of island biogeography proposed that the lower number of species on islands was not the result of insufficient time, but rather the result of an equilibrium process peculiar to all islands.

20. Island Biogeography Studies of species on islands has led to the development of a model that allows one to predict numbers of species Island biogeography model (MacArthur and Wilson, 1967)  -central observation is species-area relationship. Islands with large areas have more species than islands with smaller areas Figure 7.8 The theory is based on the idea that, at any given time, the number of species on an island is the result of a balance between two processes: extinction and colonization. When a new island forms, species begin to colonize. As more and more species accumulate, the colonization rate begins to decline. The extinction rate, on the other hand, begins to increase with increasing diversity. At some point, the two processes balance each other, and the number of species on the island should stabilize. This equilibrium number is known as S

21. Island Biogeography

22. Island Biogeography The equilibrium theory can also be used to explain the effect of size and distance on the number of species found on islands. Consider two islands of similar sizes but different distances from the mainland pool. Since extinction rates are a function of the available resources and should be related to the size of the island, we would expect them to be similar on the two islands. Colonization rates, however, should be greater for the island near the mainland than for the more distant island.

23. Island Biogeography This should result in a difference in the equilibrium number of species, with Nnear > Nfar

24. Island Biogeography A similar argument can be used to explain the effect of island size. If two islands are of relatively equal distance from the mainland, one can expect colonization rates to be similar. Extinction rates, however, should be greater on the smaller island. Therefore, we expect a higher equilibrium number of species on the large island. The two approaches (nonequilibrium and equilibrium) make very different predictions about the nature of island species. • The equilibrium theory predicts that the number of species will not change over time. The nonequilibrium theory predicts that the number of species should increase with time. • The equilibrium species predicts that, although the number of species will remain relatively constant, the actual makeup of those species will change.

25. Island Biogeography In 1969, E.O. Wilson and Daniel Simberloff conducted an experiment employing mangrove islets in the Florida Keys. Their experiment:

26. 7.8 The number of species on an island can be predicted from the area of an island

27. Species-Area relationship Species-area relationship can be summarized by the empirical formula: S = CAZ S=number of species on an island or habitat fragment C=constant dependent on the type of island and species. It is less where the quality of the environment is poorer and the total number of organisms is smaller. It also decreases with increased isolation of the island. A=area of the island Z=exponent that determines the slope of a curve where species numbers are plotted against island area. The m-value in y=mx+b. Z-values are typically about 0.25 with range of 0.15-0.35.

28. Problems from textbook Ex. C = 1, Z=0.25 for raptorial birds (birds of prey) on an island. How many species would you expect to find on islands of a. 10, b. 100, c. 1000, and d. 10,000 km2?  a. S = (1) 100.25 (10 yx 0.25 = or 10^0.25enter) = (1) (1.79) = 2  b. S = (1) 1000.25 = (1) (3.16) = 3  c. S = (1) 10000.25 = (1) (5.62) = 6  d. S = (1) 10,0000.25 = (1) (10) = 10 -tenfold increase in island size does not result in a tenfold increase in the number of species (increase is about a factor of two)

29. MacArthur and Wilson MacArthur and Wilson found that the number of species on an unoccupied island will increase over time, since more species will be arriving or evolving than are going extinct, until the rates of extinction and immigration are balanced Figure 7.9 -extinction rates will be lower on large islands than on small islands because larger islands have greater habitat diversity, a greater number of populations, and present a larger target for immigrants (green and orange lines on graph) -immigration of new species will be higher for islands near the mainland than for islands further from the mainland because mainland species are able to disperse to near islands more easily (blue and red lines on graph)

30. 7.9 Island biogeography model. Blue & red = immigration rates; green & gold = extinction rates

31. Species-area relationships Species-area relationships can be used to predict the number and percentage of species that would become extinct if habitats were destroyed. -calculation assumes that reducing island habitat would result in the island being able to support the number of species found on a smaller island -this holds true for islands and habitat islands (fragments) -model predicts that when 50% of an island is destroyed, about 10% of the species occurring on the island will be eliminated; 90% of an island is destroyed, about 50% of the species occurring on the island will be eliminated; 99% of an island is destroyed, about 75% of the species occurring on the island will be eliminated. Figure 7.10

32. 7.10 According to the island biogeography model, the number of species present in an area increases asymptotically to a maximum value

33. 7.11 Ringtail possums in habitat fragments less than 10ha go extinct in under 10 years.

34. Habitat Fragments Two important phenomena prevent habitat fragments from conforming to island biogeography theory: • Habitat diversity may be more important than area. This is true on oceanic islands as well, but the effect seems to be magnified in habitat fragments. • The formation of a habitat fragments create an “edge effect”. This refers to a change in physical and biological characteristics of a habitat as one moves from the edge to the interior (core of the fragment). Island biogeography theory has had serious ramifications for conservation. One of the most significant anthropogenic influences on natural habitats has been the fragmentation of habitats into smaller and smaller “islands”.

35. Habitat Fragments Mammal diversity in Mt. Rainier National Park has decreased by 26% between 1920 and 1976. This is probably due to the increasing fragmentation of forest habitats around the park due to logging and increased edge effect, which favors edge species over core species.

36. We would like to use our increasing understanding of island biogeography theory to assist in solving practical conservation problems. Two areas are of particular interest: • Using the theory to predict the effects of habitat fragmentation. • Using our knowledge of species-area effects to design nature preserves that will maximize long-term species diversity.

37. Ecologists have proposed landscape structure can influence movement of organisms between potentially suitable habitats. Rate of movement of individuals between subpopulations can affect species persistence in a landscape. General definition: Metapopulation: population divided into discrete subpopulations linked by movement of individuals. Subpopulation: because the landscape is heterogeneous, individuals can form smaller groups, with much less interaction between groups than if the habitat were homogeneous.

38. Four traits of metapopulations 1. The suitable habitat occurs in discrete patches that may be occupied by local breeding populations. 2. Even the largest populations have a significant risk of extinction. 3. Habitat patches must not be too isolated to prevent recolonization after local extinction. 4. The dynamics of local populations are not synchronized (all populations move together). Metapopulations are a balance between colonization and extinction.

39. Extinction Rates in Water -Extinction rates in oceans appear to be low but this is likely an underestimate as these areas are often poorly known and/or marine species may be able to adapt to disturbance well -Only four marine mammals (Carribean monk seal, Sea mink, Stellar's sea cow, Japanese sea lion), five birds, four mollusks (limpet) are known to have gone extinct in oceans. Large numbers of aquatic/wetland animals are in danger of extinction in USA Figure 7.7

40. 7.7 Dams, irrigation systems, polluted runoff, introduced species, and habitat destruction threaten aquatic species like fish and mussel species shown below:

41. In addition to global extinctions on mainlands, islands, and aquatic ecosystems, a series of local extinctions or extirpations are occurring across the range of many species in all types of habitats developed by people Ex. Chelone field work American Burying Beetle Figure 7.11 -estimated that five million populations are lost per year in tropical rain forests (13,500 populations/day)

42. Chelone obliqua L., a threatened wetland species in many states has had numerous local extinctions based on fieldwork by Nelson (1995)

43. 7.12 The American burying beetle is now found only in four isolated populations