ANT 154BN-11 Life history

ANT 154BN-11 Life history - ANT 154B Lecture # 11 Life...

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Unformatted text preview: ANT 154B Lecture # 11 Life history theory 10 Feb 2011 Life history theory 1. (Very) basic life history theory 2. Some thoughts on primate life histories 3. Linking ecology, life history, and evolution: orangutans as a case study Life history theory >1. (Very) basic life history theory 2. Some thoughts on primate life histories 3. Linking ecology, life history, and evolution: orangutans as a case study Life history theory: trade offs Resources are limited. Life is a zero-sum game. Natural selection shapes allocation “decisions”. Life history decisions: how to allocate limited resources? Investment (time and resources) Somatic effort (growth, maintenance and repair) Reproductive effort Parental effort (offspring quality - survival, growth, learning, social connections, etc) Mating effort (copulations) Life history trade offs: examples growth vs. reproduction reproduce now vs. reproduce later long juvenile period vs. short juvenile period little investment per offspring, many offspring vs. vs. intense investment a few offspring paternal investment mating effort Shaped by NS, allocate to * * maximize inclusive fitness Life history theory 1. (Very) basic life history theory >2. Some thoughts on primate life histories 3. Linking ecology, life history, and evolution: orangutans as a case study Primates typically have slow life histories Small litters Long pregnancy & juvenile period Long life span Primates: life in the slow lane Number of offspring Body weight Primates have relatively small litters Charnov & Berrigan 1993 Primates: life in the slow lane Average adult lifespan Age at maturity Body weight Primates have long lifespans and mature late Charnov & Berrigan 1993 The puzzle of primate life histories Why do primates live so long? Why do primates grow so slowly? Why do primates live so long? 1. “Rate of living” theory high metabolic rate -> early death errors metabolism toxic byproducts death Why do primates live so long? 1. “Rate of living” theory test: does low metabolic rate -> long life ? (e.g., turtles) X bats, primates: 2–3 x expected life span, average MR X marsupials: short life span, low MR Little support. Why do primates live so long? 2. Large brains are homeostatic test: large brains -> long life (e.g., primates) X bats: long life, average brain (80% average mammal) X mammals: relative brain volume not correl. w/ lifespan X primates: adrenal gland size better predicts life span than brain size. Little support. Why do primates live so long? 3. Senescence theory low environmental hazard -> long life high environmental hazard = high extrinsic mortality when high extrinsic mortality, “faustian alleles” impose few costs tests: √ √ laboratory Drosophila senescence correl w/ mortality safe animals live long (e.g., turtles, bats, birds, gliding mammals) Why do primates live so long? 3. Senescence theory low environmental hazard -> long life extrinsic mortality (on adults) -> life span primate live long b/c low extrinsic mortality Good support. Why do primates grow so slowly? 1. Brains demand energy (tradeoff brain vs. body) test: large brain correl. w/ slow growth X X bats, snakes: slow growth, small brains calorie tradeoff in primates: body growth 40% below mammals brain size/energy requirements << 40% above mammals Little support. Why do primates grow so slowly? 2. Brains demand learning logic: takes time to develop adult skills but why not grow quickly, then learn? (e.g., birds) growing quickly should be favored b/c being a juvenile is risky (higher predation on juveniles vs. adults) (assumption: must grow slowly to learn well?) ? Why do primates grow so slowly? 3. To reduce mortality risk Logic: • primate juveniles susceptible to starvation, predation • slow growth can reduce risk of starvation • protection of group living reduces predation risk, allowing slower growth *slow growth is an evolved response to reduce mortality risk* Janson & van Schaik 1993 3. To reduce mortality risk e.g., juvenile capuchin monkeys use less exposed branches (reduces feeding efficiency, and therefore growth rate, but is safer) whitefronted brown Janson & van Schaik 1993 3. To reduce mortality risk slow juvenile growth rates +/- “fixed” captive wild juvenile Janson & van Schaik 1993 Why do primates grow so slowly? 4. Low food abundance Logic: primate food too scarce to permit rapid growth predict: species with lower quality, more abundant food, grow faster Wrangham, unpublished 4. Low food abundance high quality food = less food = slow growth relative age at female maturity relative diet quality female age at maturity diet quality log Body weight log Body weight Male Gorilla Velocity (kg/yr) Weight (kg) Chimp Bonobo Age (yrs) Age (yrs) Female Weight (kg) Gorilla Velocity (kg/yr) Chimp Bonobo Age (yrs) Age (yrs) Leigh & Shea 1998 Life history theory 1. (Very) basic life history theory 2. Some thoughts on primate life histories >3. Linking ecology, life history, and evolution: orangutans as a case study Orangutan distribution Borneo Sumatra Estimated maximum range Sumatran orangutan Bornean orangutan from Caldecott & Miles (2005) World atlas of great apes and their conservation Study sites Sekundur Sekundur 23 1 Danum Valley Barito Ulu Gunung Palung Kinabatangan 9 Kutai Ketambe 6 7 8 Suaq Belimbing 4 5 Sungai Wain Tanjung Puting unlogged sites (n = 9) logged sites (n = 4) Sebangau Tuanan Morphology West Chewing apparatus smaller East bigger Taylor JHE 2006 West Brains bigger East smaller Female brain size Taylor & van Schaik 2007 West Morphology gracile, smart East big, dumb van Schaik, Marshall, & Wich 2009 Diet Percent fruit in the diet 100 90 80 70 60 50 40 30 20 10 0 0.5 P. abelii 1 1.5 P. p. wurmbii 2 2.5 P. p. morio 3 3.5 Wich et al. 2006 Percent veg in the diet 80 70 60 50 40 30 20 10 0 0.5 P. abelii 1 1.5 P. p. wurmbii 2 2.5 P. p. morio 3 3.5 Wich et al. 2006 Fallback foods Sumatra: figs Borneo: cambium (inner bark) Percent cambium in the diet 60 50 40 30 20 10 0 0.5 1 1.5 2 2.5 3 3.5 Wich et al. 2006 P. abelii P. p. wurmbii P. p. morio Fig stems per ha 14 12 10 8 6 4 2 0 0.5 1 1.5 2 2.5 3 3.5 P. abelii P. p. wurmbii P. p. morio Marshall et al. 2006, 2009; Wich et al. 2006 West Diet quality high More fruit Fewer leaves Less bark East low Less fruit More leaves More bark Taylor JHE 2006 Population density Orangutan density on Sumatra and Borneo Sumatra Borneo West Pop. density high East low van Schaik, Marshall, & Wich 2009 Forest productivity 30( 11 Percentage of trees fruiting on Borneo and Sumatra 3/( !"#$"%&'(")*+)+#,-& 2/( 10( 30( !"#$"%&'(")*+)+#,-&-%()&#"".) 20( 11 9 1/( 2 0( 1 4 6 7 8 10 3/( 2/( 9 !"#$"%&'(")*+)+#,-&-%()&#"".) 20( /( 10( 12 1/( 2 0( 1 3 6 7 !"#$%&'( Borneo: 1= Barito Ulu, 2 = Gunung 3 Palung AB, 3 = Gunung Palung LG, 5 4 = Gunung Palung LS, 5 = Sungai Wain, 6 = Gunung Palung, 7 = Tanjung Puting, 8 = Gunung Palung )*%+( ,-.*"-&* !"#$%&'( )*%+( 2/( Sumatra: 9 = Ketambe, 10-12 = Suaq Balimbing 10( 4 5 8 6 7 8 10 12 Figure 3 1/( 2 0( 1 /( 3 4 5 10 !"#$%&'( )*%+( ,-.*"-&* !"#$%&'( )*%+( ,-.*"-&* estimates of the percentage of mean Graph of time-series corrected model fruiting trees and 95% confidence intervals separated by habitat type. /( Figure 3 !"#$%&'( )*%+( ,-.*"-&* !"#$%&'( )*%+( ,-.*"-&* Wich et al. in prep Figure 3 Periods of fruit scarcity are less common on Sumatra Marshall et al. 2009 Marshall et al. 1170 FIGURE 3.4 Comparative phenology of Borneo and Sumatra 38 West Habitat good 1175 Orangutan density (direct obs/km2) 8 7 6 5 4 3 2 1 0 a East crummy 1180 1185 Marshall et al. FIGURE 3.4 8 Comparative phenology of Borneo and Sumatra 38 -1 0 .5 1 1.5 Log (Total stems/ha LFP+1) 2 1190 7 6 5 4 3 2 1 0 -1 0 .5 1 1.5 Log (Total stems/ha LFP+1) a 1195 Orangutan density (direct obs/km2) 6 5 4 3 2 1 0 Orangutan density (direct obs/km2) absent 1200 1205 2 b 0 50 100 150 Dipterocarp density (stems/ha) ect obs/km2) 6 1210 5 4 Marshall et al. 2009 Marshall et al. 2009 West Habitat good East crummy Predators present absent van Schaik, Marshall, & Wich 2009 Sociality & culture Female sociality (mean adult party size) 2 1.8 1.6 1.4 1.2 1 0.5 1 1.5 2 2.5 3 3.5 Delgado & van Schaik 2000 P. abelii P. p. wurmbii P. p. morio Culture Sociality sophisticated high limited low van Schaik, Marshall, & Wich 2008 Life history Inter birth intervals (years) 10 9 8 7 6 5 0.5 P. abelii 1 1.5 P. p. wurmbii 2 2.5 P. p. morio 3 3.5 Wich et al. 2008, Ancrenaz unpublished West Life history slow East fast van Schaik, Marshall, & Wich 2009 West Habitat Morphology Pop. density Sociality Life history Culture good gracile, smart high high slow sophisticated crummy big, dumb low low East fast limited Explanation: volcanic Sumatran soils are more fertile Mechanism? Phenotypic plasticity • flexible party sizes, day ranges, etc. • development in response to loading Local adaptations (genetic) • ability to process LQ FBFs? • gregarious predisposition? • IBIs Social learning: cultural repertoires differ due to learning van Schaik, Marshall, & Wich 2009 Hypothesized relationship between ecology and social organization of orangutans van Schaik, Marshall, & Wich 2008 Take home messages 1. Natural selection shapes allocation “decisions” among different life history strategies to maximize inclusive fitness. 2. Primate life histories are atypical compared to other mammals (e.g., live long, grow slowly). 3. Behavior, morphology, sociality, and life history show a clear west to east gradient among orangutan populations. 4. Patterns of resource availability appear to explain this pattern. 5. Mechanisms underlying these difference may be a complex interplay of phenotypic plasticity and local genetic adaptations, plus some social learning (but we don’t really know yet). Question to ponder There is considerable variation among orangutan taxa in their morphology, diet, life history, and social behavior that seems to map well onto variation in patterns of resource availability among sites (and ultimately, seems to depend on soil quality). Even if we assume that these differences are adaptive (i.e., ignoring genetic drift as a possible explanation), the extent to which these differences are evolved, genetic adaptations to local conditions or represent phenotypic plasticity is unclear. Briefly describe two ways that you might be able to tease these two alternatives apart, either through field studies, captive observations, or experiments. ...
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