How does variation in niche act as a basis for natural selection?

Transcription

1 Terrestrial Ecology

2 How does variation in niche act as a basis for natural selection? For natural selection to work you need: variation within a population at least some heritability somehow related back to fitness Different niches have different rewards and risks Wolf-Deer relationship using isotopic data Questions: Do isotopes track niches? Do different niches have different risks of being eaten? How do niches differ between survivors and non-survivors?

3 Study area is British Columbia, Canada -->wet, temperate climate, coniferous forest. There's lots to eat and lots to be eaten Focused on 3 ares: Haida Gwaii (age, gender, nutritional condition) Multiwatershed and Yeo Island (hair samples of survivors and non-survivors ) Yeo Island (how does hair isotopically relate back to niche?)

4 Results: Haida Gwaii: Age, gender, and nutritional condition did NOT affect isotopic signatures. Multiwatershed and Yeo Island: N and C isotopic signature indicate a great diversity in foraging niche.

5 More focus on survivor/non-survivor:

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7 Isotopic composition of tissues indicate shifts in diets Isotopic specialist = same isotopic composition through time; can still be dietary generalists Look at three Chilean birds: Cinclodes oustaleti (isotopic and dietary generalist, varies seasonally, Clinclodes patagonicus (isotopic specialists and dietary generalists, less seasonal variation), Cinclodes nigrofumosus (should be an isotopic and dietary specialist, no seasonal variation)

8 Dietary specialization:

9 Methods:

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12 Results: C. oustaleti: No overlap in distribution of δ13c and δ15n; 13C and 15N depleted in summer feathers to those tissues (liver, muscle)deposited in winter. Collagen was intermediate between the two C. patagonicus: Some overlap of δ13c and δ15n; significant, but smaller differences C. nigrofumosus: Smaller δ13c-δ15n area; collagen was slightly more positive than in the other species Conclusions: C. nigrofumosus has a compact isotopic niche, no seasonal variation C. oustaleti has a broad isotopic niche that varies seasonally C. patagonicus has a broad isotopic niche, but there is no real difference, isotopically, between summer and winter.

13 Modern and ancient wolves are not the same! Genetically not related Craniodental Morphology is different Tooth wear is different (bone consumption?) Stable isotope analysis!

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15 Questions: How do you look at long term environmental conditions and responses to understand processes? Focus is on local and regional climate change and how these factors affect species richness and trophic structure of Miocene mammals in sub-himalayan alluvial plains Climate affects populations by: forcing them to shift in geographic location fragmenting populations selective filtering (verify) These processes result in extinction, allopatric speciation, and biotic turnover. But the fossil record does not necessarily agree with these predictions...especially with regards taxonomic richness and rates of extinction and origination.

16 How do you resolve this problem? Take a case example: Siwalik Group = alluvial sediments located in northern Pakista >4,000 m thick and ages from 18 Ma to 1 Ma Very controlled with regards to time Good mammalian fossil record (over 50,000 specimens) Common = artiodactyls (pigs and cows, even-toed ungulates), perissodactyles (horses, Rhinos, tapirs, odd-toed ungulates), and rodents Uncommon = primates, carnivores, proboscideans Rare = creodonts (extinct carnovores), lagomorphs (rabbits), aardvarks, and tree shrew

17 Specifically used stable isotoped data (C and O) to compare and contrast environmental shifts in paleosols (vegetation) and mammalian tooth enamel (diet). Focused on a time slot of about 10.5 to 5.5 Ma Isotopic data from the paleosols indicate that the plain was initially C3 dominated (included forest, woodland, grassland, some lacustrine deposits; carbonate nodules Indicate seasonal evapotranspiration But, there's a shift that takes place (isotopically, δ13c become enriched) from abou 8.5 to about 6 Ma ago indicating that C4 became dominant (paleosol data, not Mammalian) Also a shift in δ18o from both pedogenic carbonates and teeth (at about 9 Ma) which could indicate increases in temperature, decreases in precipitation, or a change in precipitation source (this is the onset of the modern monsoon system). The number of crocodile species

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19 Expectations: If the regional climate shift is this dramatic, we should see equally dramatic changes in animal species populations C3 dependent species should die off during this transition from C3 to C4 New lineages should arrive in the area that have either a C3-C4 combination and C4 diet Shift from frugivores/browsers to feeders/grazers

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21 Before 8.5 Ma = Wet, monsoonal forest By 7.0 Ma = Dry, monsoonal forest After 6.0 Ma = Savannah From Ma there is less rain each year, but the seasonality with regards to precipitation remains the same