Interactions between organisms and their environment are the basic selective forces that drive adaptive evolution. As climatic changes impose new selective pressures on plant populations, it is becoming ever more important to understand the physiological and evolutionary responses of organisms to changing environments. My research combines theoretical, observational and experimental tools to understand how environmental factors influence the physiology and ecology of temperate and tropical plant and insect populations.

Major Research Projects

I. Plant trait variation across elevation and latitude

Understanding patterns of physiological adaptations and species diversity across latitudinal and elevational gradients are two of the most widely studied questions in ecology. To elucidate the mechanisms underlying the latitudinal diversity gradient many hypotheses invoke the importance of local abiotic and biotic processes. One such hypothesis predicts that abiotic factors should increasingly constrain diversity at higher latitudes while biotic factors are thought to be more constraining at low latitudes (MacArthur 1972). However, connecting broad biogeographical diversity patterns to local ecological studies has been challenging. This is among the few studies to assess the influence of local abiotic and biotic factors on community assembly across latitudinal gradients. (manuscript in prep for JVS special issue)

2. II.Functional diversity and succession in a dry tropical forest
   

The dry tropical forests of Sector Santa Rosa, ACG, are a mosaic of old growth, mesic forests; early successional, xeric forests; as well as forest stands of intermediate age. This results in a ‘patchwork’ distribution of species composition and ecosystem functioning within the larger tropical dry forest landscape. However, it is unclear how successional processes influence functional diversity, and thus ecosystem functioning, through space and time. In 2010, I mentored two undergraduate students (V. Buzzard and T. Birt, manuscript in prep) to pursue this and related questions.

      Xeric, early successional forests          Mesic, old growth forests- “Bosque Humedo”

III. Plant - Insect Food Webs in Tropical Forests

In collaboration with Sal Agosta (currently at Wilkes Univ.) and Jennifer Powers (UMN), we are assessing the interaction between plant functional traits and herbivore diversity. We are able to utilize an extensive database constructed by Dan Janzen, Winnie Hallwachs and many parataxonomists over 30 years within Area De Conservacion Guanacaste (see http://janzen.sas.upenn.edu/caterpillars/database.lasso) to assess if Lepidoptera diversity across plant species can be predicted by plant trait values. We ask are generalist Lep species found more often on plant traits with high Nitrogen, Phosphorous and/or water content (traits found to be, in general, ‘ideal’ for growing caterpillars)?

Related Research Projects

I. Growth-Reproduction Tradeoff in Bursera simaruba

From 1976-1986 GC Stevens measured growth and reproduction of approximately 200 female individuals in the San Emilio Forest Plot in Santa Rosa Sector of Area de Conservacion Guanacaste, Costa Rica as well as the growth of 400 males (Stevens 1987). I have used this data to assess the role of climate in determining the strength of the growth-reproduction tradeoff. LINK TO PREPRINT CLICK HERE

II. Variability in Height-Diameter Allometry across the Continental United States

Using the US Forest Inventory Analysis dataset, my collaborators and I have assessed the role of climate on inter- and intraspecific variation in height-diameter relationships. (IN REVIEW)

III. Other Projects

Though my research interests are broad and cover topics ranging from physiology, ecology, evolution and biogeography, quantifying the degree, patterns and drivers of trait variation underlies most of my research projects. Natural selection would be meaningless without variation. Describing the importance and role of variation will provide further insight into the evolution of functional traits and the underlying mechanisms of species coexistence.

Study Systems

Area de Conservacion Guanacaste, Costa Rica

Santa Elena Peninsula in northwestern Costa Rica primarily consists of serpentinized ultramafic rocks with local volcanic, sedimentary and alluvial deposits. Although Santa Elena Peninsula lies within the dry tropical forest life zone, evergreen forests can be found along riparian valleys and cloud forests populate the higher elevation ridges (read more about a recent expedition to Santa Elena Peninsula, click here and here). The proximity of different soil types (often within 100m of each other) at low altitudes facilitates a comparison of inter- and intraspecific variation in plant traits and provides accessible locations for reciprocal transplant experiments across various soil types of similar climate. The altitudinal gradient from sea level to 700m across serpentine derived soils allows for a descriptive test of inter- and intraspecific trait variation and inheritance across a climatic gradient.

Palo Verde National Park, Costa Rica

Located approximately 120km southeast of Santa Elena Peninsula, Palo Verde National Park consists of dry tropical forests on alluvial soils and limestone outcrops and an extensive wetland ecosystem.

Susua and Guanica, Puerto Rico

Dry tropical forests are found on limestone and serpentine outcrops in these southwestern forests and provide a further test of inter- and intraspecific trait variation.

Shreve, Whittaker and Niering Gradient, Catalina Mountains, Tucson, Arizona, USA

The gradient from desert to alpine forests provides an excellent “temperate” analog to test Janzen’s Mountain-Pass Hypothesis. This, in conjunction with the dry forest, cloud forest, rainforest gradient in ACG should provide an excellent test of trait variability across both temperate and tropical gradients.

Siskiyou Mountains, Oregon

The gradient from mixed evergreen, montane to subalpine forests provides a high latitude temperate system for testing Janzen’s Mountain Pass Hypothesis as well as other hypotheses of community assembly.