I am a community ecologist whose interests lie broadly in the fields of basic and applied ecology, particularly biodiversity conservation and ecological restoration. My current research (and that of my dissertation) seeks to understand how contemporary patterns of plant adaptation to environmental clines (e.g. across latitude and elevation) will mediate responses to predicted environmental change and subsequently influence plant-animal interactions. I then seek to determine the implications of my results for conservation and restoration of these communities in a changing environment. Within this framework I ask questions such as:
My dissertation research examined geographic variation in plant traits and arthropod communities for populations of Artemisia californica (California Sagebrush) over 700 km of its range across a five-fold precipitation gradient in coastal California. Artemisia californica is a dominant species in coastal sage scrub (CSS) habitat, which has been reduced to 10-15% of its historical distribution in the past several decades as a result of land-use change. It is therefore considered one of the most threatened plant communities in the United States. Many CSS restoration efforts focus on establishing a shrub layer consisting of plants such as A. californica that are used by endangered animal species. The current paradigm for CSS restoration involves two particular issues that my work directly addresses. First, it is mainly focused on plants, assuming that if the plant community is restored, the animal community will return. While community-level responses to environmental change may be driven in large part by the response of foundational species like A. californica, this is rarely documented or monitored. Second, most restoration is focused on using the most local plant material possible, assuming that plants nearby will do the best because they are evolutionarily adapted to the local environmental conditions. This approach does not consider that the environment is, and will continue to change in ways that affect plant persistence and restoration success. As such, I aimed to determine how both genetically based population variation in A. californica traits and variation in its response to environmental change scaled up to affect arthropod communities. Not only are arthropods the primary food source for California’s most threatened bird and reptile species, they constitute the majority of multicellular species diversity in terrestrial systems. While largely unseen, the arthropod community on A. californica alone consists of more than 225 species, often occurring in densities of >500 individuals*m3(-1) of plant tissue.
Through this research I’ve shown that A. californica populations grown within a common garden vary clinally in many functional traits including growth rate, nutrient content, secondary chemistry, and the timing of reproduction, thus providing strong evidence for local adaptation to this environmental cline (Pratt and Mooney 2013, Global Change Biology; Pratt et al. 2014, Oikos). Furthermore, plant populations exhibited striking variability in growth and reproduction in response to altered precipitation; my data indicates that northern populations may be less able than southern populations to tolerate predicted environmental changes. Additionally, there were plant genetic effects on arthropod abundance, diversity and community composition, providing evidence of extended consequences of clinal adaptation for A. californica’s associated animal community.
Master's Thesis Research
For my Master's thesis research, I assessed the conservation value of shaded coffee plantations and secondary forests in Puerto Rico for resident avifauna and examined the influence of nesting location and habitat type on nest predation rates. As size and number of undisturbed forests dwindle due to human encroachment, the importance of disturbed areas, such as secondary forests and shaded coffee plantations, for conservation of avifauna has risen. These “functional substitutions” are not only recognized and valued at present, but in some cases, they may have played important conservation roles in the past.
I analyzed data collected from 1997-1999 on the reproductive activity and productivity of resident avifauna in shaded coffee plantations and secondary forests in Puerto Rico. Data collected from a survey of >250 nests showed that shaded coffee plantations and secondary forests did not differ in terms of species composition, nest success, or breeding productivity. Nest predation and nest abandonment each accounted for 38% of nest failures. The production capacity of shaded coffee plantations was dependent on nesting substrates provided by the shade vegetation (canopy) layer, not the coffee tree layer. Nesting activity in secondary forests also occurred primarily in the canopy layer (Gleffe et al. 2006, Ornitologia Neotropical) . To investigate the basis of this pattern, I tested whether the observed nesting patterns were influenced by differential predation pressure between the understory and canopy layers. I also tested whether predation pressure differed between canopy layers of plantations and secondary forests to further assess the conservation value of shaded plantations. Tests were conducted using a series of carefully designed artificial nest experiments during the breeding season of 2005. I found that predation rates ranged from 0.44 to 0.77 (average = 0.65 ± 0.06 SE) for understory and from 0.45 to 0.80 (average = 0.65 ± 0.05 SE) for canopy nest heights. Predation rates ranged from 0.67 to 1.0 (average = 0.84 ± 0.06 SE) in shaded coffee plantations, and from 0.63 to 0.97 (average = 0.81 ± 0.06 SE) in adjacent secondary forest. Rates for both experiments were not significantly different (P > 0.05). Based on photographic evidence, avian and mammalian nest predators can prey upon nests regardless of height. Experiments and data from natural nests suggest that birds nesting in shaded plantations are not at a disadvantage compared to those nesting in secondary forests (Gleffe 2005, M.S. Thesis). This finding, coupled with the fact that shaded coffee plantations were more widespread in the past and were managed as rustic plantations and traditional polycultures (resembling primary forests), lends considerable support to the notion that shaded coffee plantations have served as a refuge for resident avian species during periods of widespread deforestation. Moreover, the pervasive nature of nest predation reported in this work, and its influence on habitat quality, affirmed the need to identify and manage habitat features associated with nest success.