Browsing by Subject "biogeography"

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    Biotic interactions and edaphic variation modulate geographic range limits in Clarkia xantiana ssp. xantiana
    (2019-09) Benning, John
    The study of species’ geographic distributions, especially limits to those distributions, lies at a fruitful nexus of ecology and evolutionary biology. At these distributional limits, the ecological interactions that determine population mean fitness across and beyond the range limit collide with the evolutionary limits to adaptation. Species’ geographic distributions comprise the spatial extent of their populations, and vary greatly in size, shape, and the arrangement and abundance of populations contained therein. However variable these distributions are, they all are bounded by an invisible perimetric line on the landscape beyond which populations of that species cannot be found, i.e., the species’ geographic range limit. Why are individuals able to persist on one side of this border but are excluded from regions directly adjacent? This deceptively simple question is a perennial one that underlies many foundational questions about ecological interactions and adaptation. Distributions are structured by myriad factors with large, small, and interactive effects, but the essential determinants of the spatial patterns are relatively simple — populations persist where long term growth rates are equal to or greater than replacement (λ ≥ 1). But given sufficient time and adequate heritable variation for ecologically important traits, species’ ranges should theoretically be able to continually expand outward through sequential adaptation by populations at the range edge. Of course, this is not the observed pattern in nature; most species are restricted to a relatively small fraction of the planet’s available habitat. This dissertation is an attempt to untangle the complex environmental gradient that occurs across and beyond C. x. xantiana’s distribution, and evaluate the relative importance of precipitation, mammal herbivory, pollinator limitation, and biotic and abiotic edaphic factors in setting the subspecies’ geographic range margin. In Chapter 1, I focus on fatal mammal herbivory and evaluate its potential as a range limiting factor, with a conceptual approach based on foundational range limits theory. I show that probability of herbivory increases sharply near and beyond C. x. xantiana’s range margin, that this interaction has large effects on population mean fitness at the transplant site beyond the range edge, and that susceptibility to herbivory is largely mediated by plant phenology. In Chapter 2, I follow up on these results with a large field experiment at multiple sites inside and outside the range, estimating the effects of geography, source population, herbivory, and pollen limitation on lifetime fitness across two years. Protection from herbivory and supplementation of pollen increased plant fitness three to seven-fold outside the range margin, and there was only limited evidence of local adaptation of C. x. xantiana populations. Both of the transplant experiments reported in these chapters captured both a relatively wet and a relatively dry year, and showed that the effect of herbivory on population mean fitness differed across abiotic contexts — in dry years, precipitation limited fitness outside the range edge, but when C. x. xantiana was largely “released” from abiotic stress wet years, herbivory strongly limited population mean fitness. Chapters 3 and 4 focus on belowground - aboveground interactions. In Chapter 3, I use greenhouse and field experiments to ask how spatial variation in soil microbial communities influences plant local adaptation and the potential for range expansion in C. x. xantiana. Microbial communities from one site inside the range positively affected components of fitness in both the greenhouse and field, especially near to and beyond the range margin, and there was no evidence of local adaptation to microbial communities among plant populations. In Chapter 4, I report on an intensive field experiment where I factorially manipulated complete (i.e., biotic and abiotic) edaphic environments (growing plants with soil sourced from either within or beyond their native range) and precipitation to quantify the relative effects of within-range soil and increased precipitation on C. x. xantiana fitness outside its range margin. Across two years, edaphic environment had large effects on plant lifetime fitness that were similar in magnitude to the effects of precipitation. Moreover, mean fitness of plants grown with within-range soil in the low-water treatment approximated that of plants grown with beyond-range soil in the high-water treatment.
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    Ecology and Evolution of Geographic Range Size Variation in North American Plethodontid Salamanders: Perspectives from Thermal Physiology
    (2015-07) Markle, Tricia
    Species exhibit remarkable variation in geographic range size. Understanding the causes of this variation is fundamental to the fields of ecology and evolution, and is central to understanding how species will respond to rapid climate change. Using eastern North America's species-rich salamander fauna, I explore whether seasonal variation in temperature and climatic tolerance evolution underlie geographic range size variation (as per the climate variability hypothesis). First, I determined critical thermal maximum (CTMax) and critical thermal minimum (CTMin) temperatures of 18 salamander species. I then tested for relationships between thermal tolerances, seasonality, and geographic range size. Localities with greater annual temperature ranges (seasonality) were found to have individuals with broader thermal tolerances, and correspondingly species with larger latitudinal extents. Intraspecific tests, however, found only one of six wide-ranging species to relate thermal tolerances to environmental temperature changes across the range. Next, I estimated acclimation ability of salamanders to see if species with larger distributions have greater physiological plasticity. Salamanders were acclimated to 14 and 22�C and results of a phylogenetically controlled MCMCglmm model indicated that there are significant differences in temperature adjusted standard metabolic rates (SMRs) of species with wide versus narrow latitudinal extents. Wide-ranging species showed a slight increase in SMR after acclimation, whereas narrow-ranging species showed a statistically significant drop in SMR. These results indicate that wide-ranging species have a greater thermal acclimation capacity than narrow-ranging species. Finally, using GIS-based climate data I included all available locality points to estimate species-level thermal niche breadths. I found that CTMax and CTMin of species are strongly correlated with the maximum and minimum temperatures that occur within their geographic ranges. I also found that species' thermal tolerance breadths (CTMax) CTMin) are highly correlated with estimates of their thermal niche breadths. My general finding that wide-ranging species have broader physiological tolerances than narrow-ranging species supports key predictions of the climate variability hypothesis and the role of seasonality in the evolution of physiological traits. It also highlights the potential vulnerability of narrow-ranging montane salamanders.
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    The Neotropical caddisfly genus Tolhuaca (Trichoptera: Glossosomatidae)
    (Magnolia Press, 2005) Robertson, Desiree R.; Holzenthal, Ralph W.
    The caddisfly genus Tolhauca Schmid 1964 (Glossosomatidae: Protoptilinae) is diagnosed and discussed in the context of other protoptiline genera, and a review of its taxonomic history is provided. A new species, Tolhuaca brasiliensis, from southeastern Brazil, is described and illustrated, and the type species, Tolhuaca cupulifera Schmid 1964, from Chile, is redescribed and illustrated. Additionally, females of the genus are described and illustrated for the first time. Characters of the female genitalia, wing venation, and thorax suggest that Tolhuaca is more primitive than any other protoptiline genus and probably deserves a basal placement within the subfamily. The genus shows a broadly disjunct distribution perhaps reflecting an ancient southern Gondwana pattern.
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    Systematics of the Neotropical caddisfly genus Notidobiella Schmid (Trichoptera, Sericostomatidae), with the description of 3 new species
    (Pensoft Publishers, 2010) Holzenthal, Ralph W.; Blahnik, Roger J.
    Three new species of Notidobiella Schmid (Insecta: Trichoptera) are described from South America: Notidobiella amazoniana sp. n. (Brazil), N. brasiliana sp. n. (Brazil), and N. ecuadorensis sp. n. (Ecuador). In addition, the 3 previously described species in the genus, N. chacayana Schmid, N. inermis Flint, and N. parallelipipeda Schmid, all endemic to southern Chile, are redescribed and illustrated, including the females of each species for the first time, and a key to males of the species in the genus is provided. The occurrence of Notidobiella in Brazil and Ecuador represents a signifi cant extension of the range of the genus beyond southern Chile where it previously was thought to be endemic. The biogeography of Sericostomatidae and other austral South American Trichoptera is reviewed. The presence of the family in South America may not be part of a “transantarctic” exchange, but instead may represent an earlier occurence in the region. The distribution of Notidobiella in tropical South America likely represents recent dispersal from southern South America to the north.