Evolutionary Patterns

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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

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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

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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

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Evolutionary Patterns
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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

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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?

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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

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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

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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

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Evolutionary PatternsCryptic Coloration

• Cryptic coloration
• Again, landscape context is the key

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Evolutionary Patterns Cryptic Coloration

• Pepper moth

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Evolutionary Patterns Cryptic Coloration

• Function is generally to protect animals from
  detection by predator

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Evolutionary Patterns Cryptic Coloration
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Evolutionary Patterns Warning Coloration

• Some sp choose not to blend

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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

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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

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Evolutionary Patterns Warning Coloration

• Of course in nature, when something has a good
  thing goingthere are cheaters (Batesian Mimicry)
• E.g. kingsnakes false sphinx moth

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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

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Evolutionary Patterns Mimicry

• Monarch and Viceroy robber fly

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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?

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Evolutionary Patterns Mimicry

• Heliconius melpomene
• and H. erato

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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

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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!!
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Evolutionary Patterns Mimicry
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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

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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)

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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

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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

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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)

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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

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Evolutionary Patterns tropical selection
pressures

• Consider a trip to Alaska in winterwhat are you
  bringing?
• How about to Manaus?

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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!!

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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

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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?

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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

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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

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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

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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

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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)

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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

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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?

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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

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Evolutionary Patterns species diversity

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

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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

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Evolutionary Patterns species diversity

• Tyrannid flycatchers

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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)

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Evolutionary Patterns species diversity

• Foraging relationship among several antbirds
  (Formicariidae)

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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

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Evolutionary Patterns species diversity

• In the absence of the other competitor, each
  species will expand its range up or down the
  mountain

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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

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Evolutionary Patterns species diversity

• If competition is so intense, it can ultimately
  lead to the extinction of one of the species
• What can prevent this?

Predation!!
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Evolutionary Patterns species diversity

• Predation Hypothesis
• Consider 4 caterpillar larvae eating the same
  plant
• What happens when one species starts to
  numerically dominate the plant?
• Predators are thought to respond to the most
  abundant prey species, thereby keeping the
  balance and allowing for greater species
  richness

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Evolutionary Patterns species diversity

• This is foraging strategy is known as
  frequency-dependent selection
• This is somewhat the opposite hypothesis of the
  competition hypothesis as predation lowers
  interspecific competition by reducing numbers,
  not narrowing niches

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Evolutionary Patterns species diversity

• There is some evidence that some predators (e.g.
  birds) develop a search image when it is
  particularly abundant
• Many cats show no preference
• A nice exclusion study in Puerto Rico, Anolis
  lizards were shown to have a dramatic impact on
  several groups of insects (not definitive, but
  suggestive)

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Evolutionary Patterns species diversity

• Productivity-Resources Hypothesis
• What if it were as simple is there is just more
  resources to divide up

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Evolutionary Patterns species diversity

• I think that there are so many species of
  insects because the world contains a very large
  amount of harvestable productivity that is
  arranged in a sufficiently heterogeneous manner
  that it can be partitioned among a large number
  of populations of small organisms
• Janzen

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Evolutionary Patterns species diversity

• Bird species diversity often correlates with
  foliage height complexity in the temperate zone,
  but not nearly as well in the tropics
• Perhaps this is due to a higher level of
  complexity, not just height
• The tropics do offer resources not found in the
  temperate zone (e.g. vines, epiphytes, dry leaf
  clusters)

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Evolutionary Patterns species diversity

• For birds, there are also dietary resources not
  available in the tropics
• There are constant supplies of nectar, fruits,
  larger insects and more insects
• Army ants provide a unique resource
• Some specialized raptors (e.g. bat falcon
  black-and-white owls, harpy eagles)

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Evolutionary Patternsspecies diversity

• Mammalian diversity also correlates with
  productivity and habitat characteristics. The
  density and number of species of Amazonian
  mammals correlate positively with soil fertility
  and undergrowth density
• Bats add a large number, but obscure many
  diversity patterns

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Evolutionary Patternsspecies diversity

• Conclusion there is little doubt the
  productivity influences the diversity of animals
  in the tropics
• But what about the diversity of plants?
• EO Wilson has the ESA theory
• E energy
• S stability
• A area

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Evolutionary Patternsspecies diversity