Evolutionary Patterns

1. Evolutionary Patterns • The tropics have long been called a ‘laboratory of evolution’ because of the extraordinary diversity of species and the complex relationships among its members

2. Evolutionary Patterns • 1859 Darwin published ‘On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life’

3. Evolutionary Patterns • The Basics: species have changed over time, they can and do change from previous ancestors. • Thus the relationships of species forms a tree (or bush) with each branch representing an evolutionary lineage • The process of how the bush developed through long stretches of time is termed ‘descent with modification’

4. Evolutionary Patterns

5. Evolutionary Patterns • There are biological and physical constraints on organisms under which it must adapt to survive (and reproduce). • Natural Selection (vs. artificial selection) is this process

6. Evolutionary Patterns • Thomas Malthus: all organisms tend to reproduce more offspring than can survive within the limits of their environment and therefore are engaged amongst themselves in a ‘struggle for existence’ • Who wins?

7. Evolutionary Patterns • Both Darwin and Wallace were strongly influenced by their time in the Neotropics • Wallace spent 4 yrs on the Amazon • Darwin went throughout South America and the Galapagos

8. Evolutionary PatternsAdaptations • An adaptation is any anatomical, physiological, or behavioral characteristic that can be shown to enhance either the survival or reproduction of an organism (and have a genetic basis) • The prehensile tail of opossums, monkeys or kinkajous is an adaptation

9. Evolutionary Patterns Adaptations • Not all adaptations are obvious • E.g. sickle-cell anemia • E.g. The ‘stabilimenta’ of orb-spiders • Not all adaptations are ‘current’ • Appendix • Thermoregulation in the tropics • Context of adaptation must be considered

10. Evolutionary PatternsCryptic Coloration • Cryptic coloration • Again, landscape context is the key

11. Evolutionary Patterns Cryptic Coloration • Pepper moth

12. Evolutionary Patterns Cryptic Coloration • Function is generally to protect animals from detection by predator

13. Evolutionary Patterns Cryptic Coloration

14. Evolutionary Patterns Warning Coloration • Some sp choose not to blend

15. Evolutionary Patterns Warning Coloration • Probably a relationship between the toxicity of many species (e.g. Dendrobatidae or coral snakes) • This is known as aposematic coloration • >300 noxious or toxic alkaloids have been isolated from various species of amphibians

16. Evolutionary Patterns Warning Coloration • Dendrobatidae have many toxins, such as batrachotoxins • Ironically, also found in pitahouis • How so toxic? • Diet appears to influence this • This is also an extremely common practice amongst butterflies

17. Evolutionary Patterns Warning Coloration • Of course in nature, when something has a good thing going…there are cheaters (Batesian Mimicry) • E.g. kingsnakes & false sphinx moth

18. Evolutionary Patterns Mimicry • In this system you have a ‘model’ and a ‘mimic’ • Obvious benefit to mimic, but what about the model? • What if a predator eats a couple of palatable insects first… • Consequently, Batesian mimicry works best when mimic is less abundant

19. Evolutionary Patterns Mimicry • Monarch and Viceroy & robber fly

20. Evolutionary Patterns Mimicry • Mullerian Mimicry • So many tropical plants have relatively nasty compounds that many species of caterpillars are probably quite unpalatable • It would be beneficial if two or more unpalatable species looked alike • Why?

21. Evolutionary Patterns Mimicry Heliconius melpomene and H. erato

22. Evolutionary Patterns Mimicry • There are eleven distinct races of H. melpomene in the tropics ranging from Mexico to southern Brazil. The races do not look the same. • Instead, there is an identical local race of H. erato!! Only one race lacks a counterpart

23. Evolutionary Patterns Mimicry • Mimicry Complexes • Through both Mullerian and Batesian mimicry, there have been extensive convergences among large groups of butterflies in the tropics • Papageorgis (1975) found five distinct color complexes, each containing multiple mimicking species… Occupying different heights in the rainforest!!

24. Evolutionary Patterns Mimicry

25. Evolutionary Patterns Mimicry • After experimentation, it turns out each is cryptically colored in flight at the height in the rainforest where it normally flies. (based upon pattern of light penetration) • This could be an example of both cryptic and warning coloration with the same species, depending upon where they are, and if flying or stationary

26. Evolutionary Patternstropical selection pressures • Factors in the environment of an organism that influence the probability of its survival or reproductive success are called selection pressures • May be seasonal stresses (e.g. fire or rain), or from the soil in the form of nutrient shortage (abiotic) • May also be biotic (e.g. competitors, predators, parasites, disease, food)

27. Evolutionary Patterns tropical selection pressures • Usually there is a combination of selection pressures at work • They may or may not be acting synergetically, or they may be acting diametrically • Over time, selection pressures will likely change

28. Evolutionary Patterns tropical selection pressures • Abiotic Selection • Although there is a strong seasonal component to the tropics, it is still relatively benign compared to much of the temperate zone • Physiologically, for most organisms it probably is much easier to live in the tropics

29. Evolutionary Patterns tropical selection pressures • Biotic Selection • there are many, many biotic pressures placed on organisms in the tropics • E.g. plants may compete with parents • E.g. most groups are very diverse, thus making many competitors, even if relatively rare (diffuse competition)

30. Evolutionary Patterns tropical selection pressures • Predators are undoubtedly a significant problem (both small and big) • E.g. consider birds nesting • In the tropics, smaller clutch size despite the apparent greater food sources • Thus, it is probably better to raise fewer chicks than a single large clutch • E.g. frogs (or katydids) calling

31. Evolutionary Patterns tropical selection pressures • Consider a trip to Alaska in winter…what are you bringing? • How about to Manaus?

32. Evolutionary Patterns species diversity • With very little exception (e.g. salamanders) the greatest number of species for most major taxa – flowering plants, ferns, mammals*, birds, reptiles, amphibians, fish, insects, spiders, and snails- is the tropics!!

33. Evolutionary Patterns species diversity • In the ‘Origin of Species’, Darwin noted that species generally increases as one travels towards the equator (termed latitudinal gradient) • Breeding Birds • Greenland 56, NY 195, Guatemala 469, Panama 1,100, Columbia 1,395

34. Evolutionary Patterns species diversity • Dobzhansky argued since diversity is a product of evolution, differences must be due to differences in evolutionary patterns • However, what selection pressures and other causes have brought about the greater richness and variety of the tropical flora and faunas?

35. Evolutionary Patterns species diversity • Dobzhansky believed the harsh physical environments of the temperate latitudes have reduced the number of organisms able to adapt to such stresses

36. Evolutionary Patterns species diversity • Difference between diversity and richness • Maximizing diversity requires a relatively constant number of individuals across species • In the tropics, several groups achieve this by a constant low abundance

37. Evolutionary Patterns species diversity • Diversity can be considered at several spatial scales • Alpha diversity – within habitat diversity • Beta diversity – the change in species composition from one habitat to another similar habitat • Gamma diversity – regional diversity across a number habitats in a large area

38. Evolutionary Patterns species diversity • So how did the tropics come to have such high diversity? • There are several theories, some of which may apply to some groups and others to other groups

39. Evolutionary Patterns species diversity • Stability-time Hypothesis • The tropics have been around so long it has had enough to for speciation to occur over and over again • However, there are many examples of rapid speciation (e.g. cichlids, kingfishers)

40. Evolutionary Patterns species diversity • The premise is sound • However, most agree the tropics have been far from stable and these fluctuations may actually have promoted speciation events • Old and stable is probably not supported

41. Evolutionary Patterns species diversity • Interspecific Competition Hypothesis • Difficult to actually assess competition • For competition, resource in question must be limiting • Also, should be negative impact on one another • If one is removed, does the other prosper?

42. Evolutionary Patterns species diversity • High competition has resulted in increased specialization • Each species has focused on a specific resource • The trend towards specialization has lead to ‘species packing’

43. Evolutionary Patterns species diversity • There is a strong historical assumption to this hypothesis, which is difficult to test (e.g. ghost of competition past)

44. Evolutionary Patterns species diversity • This is a general problem with tropical ecology: competition is circumstantial • There are good examples of varying bill shapes and gradations in body sizes within many bird groups

45. Evolutionary Patterns species diversity • Tyrannid flycatchers

46. Evolutionary Patterns species diversity • However, different size bills and bodies can also simply reflect diet specialization (i.e. just getting better) • There are several clusters of similar species that have developed differences in foraging areas and that is an indirect indication that competition may have been at work (previously)

47. Evolutionary Patterns species diversity • Foraging relationship among several antbirds (Formicariidae)

48. Evolutionary Patterns species diversity • Other examples include three flatbilled flycatchers in Costa Rica who forage at different heights • Across habitats, one species may replace another in this unoccupied ‘niche’ • Other examples include niche expansion when others are absent

49. Evolutionary Patterns species diversity • In the absence of the other competitor, each species will expand its range up or down the mountain

50. Evolutionary Patterns species diversity • There also appears to be some support for the idea that interspecific competition for pollinators has resulted in a staggered flowering pattern