Project #1
Bugs and booze: effects of urbanization and vegetation on flying invertebrate communities of temperate forests.
As human populations continue to increase, urban land cover is spreading and severely altering natural ecosystems across the globe (Fenoglio et al. 2020, Dirzo et al. 2014). The extreme change in land cover associated with urbanization and high human population density creates unique habitat heterogeneity, habitat degradation and fragmentation, increased pollution, prominence of invasive species, and elevated air temperatures (Fenoglio et al. 2020). Ultimately, these effects have been found to have a massive impact on biodiversity, particularly with respect to vegetation and invertebrates.
To counteract negative impacts to local biodiversity associated with urbanization, conservation areas and urban green spaces are created and managed to host organismal life while also serving as recreational areas for humans (González-Césped 2021, Aronson et al. 2017). However, these areas have been found to have a limited potential in terms of biodiversity when compared to more rural conservation areas (Castelli et al. 2021). Specifically, insect communities within areas of the highest level of urbanization (i.e., central urban core) have the lowest taxonomic richness when compared to their rural counterparts (Langellotto and Hall 2020, McKinney 2008).
In contrast, some taxa such as bumblebees and lepidopterans have shown increased species richness at sites of intermediate anthropogenic disturbance (i.e., suburban areas) when compared to areas of high anthropogenic disturbance (i.e., central urban cores) (Langellotto and Hall 2020, Niemelä et al. 2000, Posa and Sodhi 2006, McGeoch and Chown 1997, and Ahrné et al. 2009). The increased richness within the areas of intermediate levels of disturbance likely correlates to their relatively high plant species richness and their ability to serve as a transition from rural and urban areas (McKinney 2008, Connell 1978).
Many studies have found a similar correlation of high plant diversity/density acting as significant drivers for insect diversity (Raupp et al. 2001, Murdoch et al. 1972). Further, other landscape-level characteristics such as patch size, floral abundance, solar irradiance, and woody plant cover also affect insect diversity (Fenoglio et al. 2020). With ecosystems changing regularly as urbanization becomes more commonplace, it is essential to understand the role of urban parks in determining the diversity of insect communities and what factors drive those changes (McFrederick and LeBuhn 2006).
For this study, I aim to examine the following hypotheses: Hypothesis I: Proximity to urbanized environments will impact the community composition of invertebrate communities.
Hypothesis II: Woody plant community composition (e.g., total density, relative and absolute abundance, species frequency, and coverage) within forests will affect community composition of invertebrate communities.
Hypothesis III: Invertebrate community composition will vary based upon proximity to walking/hiking
human trails (adjacent to or far from).
Project #2
Is there no place like home? Investigating the effects of moisture gradients and invertebrate colonization on oak (Quercus) leaf litter decomposition using the homefield advantage hypothesis
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Leaf litter decomposition is a complex process that relies on physical and chemical factors including climate, leaf chemical characteristics, and the decomposer community. These three factors directly interact with and influence one another to directly affect rates of decomposition (Aerts 1997). Climatic factors (e.g., temperature and moisture) are major drivers of leaf chemical composition. In stressful environments (i.e. high moisture areas), it has been found that leaf chemical traits can be beneficial to plant survival as its linked to anti-herbivory, UV protection, moisture retention, antioxidant properties, etc. Consequently, plants occurring in different habitats will have different chemical composition of their leaves. (Swift and Anderson 1989). Similarly, leaf chemical composition is often a driver of decomposer community diversity as it controls which taxa can colonize and break-down the leaf litter due to structural compounds impacting digestibility, anti-herbivory compounds, etc.
Due to decomposition’s reliance on climate and the decomposer community, the home-field advantage (HFA) hypothesis has been proposed stating that leaf litter will decompose faster in its home habitat than in any other habitat due to habitat-specific differences in climate and invertebrate/microbial community adaptations/colonization abilities (Gholz et al. 2000). To investigate this idea, reciprocal transplant experiments with plant litter in ‘home’ and ‘away’ environments have typically been used to study habitat effects on decay rates.
One genus that has the ability to exploit a wide range of habitats globally is the oak genus (Quercus) Pin oak (Quercus palustris) and Northern red oak (Quercus rubra) in particular are an excellent example of such habitat ranges within the northern hemisphere. Quercus palustris is known to be a flood-tolerant species native to the eastern united states. This tree species is tolerant of acidic, poorly draining soils found in alluvial floodplains and bottomland habitats (McQuilkin 1990, Black 1984). Quercus rubra is tolerant of many habitats, but performs best in moist, well-drained soils associated with uplands native to the eastern united states (Sander 1990). Although both species broadly fall under the “red oak” category, these species differ in their chemical/structural components of their leaves alongside their habitat. These differences in “home” habitat of these species provides an excellent environment for studying climatic conditions such as moisture gradients.
In terms of chemical composition, it was found that the upland species, Q. rubra, has a higher C:N ratio and toughness when compared to the lowland species, Q. palustris (Ostrofsky 1997). Similarly, Quercus palustris has higher levels of tannic acid and phenol-precipitating capacity while Quercus rubra has higher levels of proanthocyanidins (Martin and Martin 1982). The variation in the amount and composition of polyphenolic compounds (e.g., tannins, proanthocyanidins, etc.) among leaves from different oak species can provide experimental opportunities to evaluate leaf litter decay in structurally similar leaves possessing a wide range of these secondary compounds.
In this study, I will investigate (1) decomposition of leaf litter from dominant oak species and the impact of soil invertebrate diversity/presence as well as habitat (moisture) on said decomposition, (2) relationships between habitat, arthropod diversity/presence, and leaf chemical composition, (3) the impact of the home-field advantage on leaf litter decomposition across a moisture gradient. To address these questions, I propose to test the following hypotheses: Hypotheses I: The abundance and diversity of arthropods, coupled with soil moisture, will affect litter decomposition rates.
Hypothesis II: The chemical composition of leaf litter will affect patterns of arthropod diversity and litter decomposition rates.
Hypothesis III: Litter decomposition rates will be enhanced for leaves in their home environment relative to other environments (Home-field advantage)
Project #3
Homefield advantage: effects of elevation gradients and invertebrate colonization on oak (Quercus) leaf litter in a tropical montane fores
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Tropical montane cloud forests are excellent sites for understanding patterns of species diversity and dominance along intense elevational gradients (Long et al. 2022). Within these forests, there are clear gradients in species distribution as elevation increases due to abrupt changes in environment. Consequently, species endemic to tropical montane cloud forests must be adapted to withstand varying levels of stress as environmental variables change drastically over short geographic distances. These communities are subject to high levels of moisture, cooler
temperatures, high wind speeds, low nutrient availabilities, lower incidence of sunlight, and high UV radiation at the highest reaches of these mountains (Bruijnzeel and Veneklaas 1998).
The necessity to survive harsh environmental conditions has resulted in shifts of species dominance, lower diversity, and differences in physical and chemical traits at high elevations (Whitmore 1989). An excellent example of this trend is the high tolerance for UV radiation in plants endemic to high elevations, where UV radiation is high due to the thin atmosphere. UV radiation represents a unique environmental stressor for plants as high UV has been linked to DNA damage, oxidation stress, and reduced plant growth (Rozema et al. 1997). The increase in UV and other stressors has often led to trees that are shorter in stature, have smaller, thicker leaves, and lower productivity at high elevations (Salinas et al. 2021). However, Quercus species found in the upper limits of the Talamanca Mountain range stand tall (>40m) with large amounts of biomass, productivity, and consequentially, a high accumulation of litter on the forest floor.
The presence of tall, highly productive Quercus species in tropical montane cloud forests provides a unique opportunity to study the mechanisms driving these communities. It is proposed that phenolic compounds are aiding in these trees’ adaptation to high UV stress accompanied by high elevation. The production of plant phenols is regulated by both the environment and genetic makeup of the plants. Moreover, plants increase production of phenols in response to environmental stress (Dixon and Paiva 1995) caused by nutrient deficiency (Demotes-Mainard et al. 2008), heat stress (Wahid et al. 2007), ozone concentration (Cabane et al. 2004), high light intensity (Hoch et al. 2001), metal toxicity (Duressa et al. 2010), pest attack (Herms and Mattson. 1992), and drought (Bettaieb et al. 2011, Griesser et al. 2015, Suseela et al. 2015).
These phenolic compounds confer valuable protection to plants growing at high elevations, firstly by acting as sunscreens, filtering-out harmful UV radiation (Meijkamp et al. 1999) and, secondly, by acting as antioxidants that prevent oxidative damage to plant cells (Grace and Logan 2000). However, while many studies have documented lignin effects on litter decay rates (Meentemeyer 1978, Gholz et al. 2000, Cusack et al. 2009), it has been found that some phenolic compounds degrade even more slowly than lignin (Minderman 1968). These compounds may significantly depress microbial and invertebrate activity and litter decay rates as they often have anti-herbivory properties (Palm and Sanchez 1991, Madritch and Hunter 2005, Schweitzer et al. 2008). Decomposition of Quercus leaf litter in tropical montane environments poses a unique environment to study the relationship between climate, leaf chemical composition (i.e. phenolics) and decomposer community.
In this study, I will investigate (1) decomposition of leaf litter from dominant oak species and the impact of soil invertebrate diversity/presence as well as habitat (elevation) on said decomposition, (2) relationships between habitat, arthropod diversity/presence, and leaf chemical composition, (3) the impact of the home-field advantage on leaf litter decomposition across a elevational gradient. My hypotheses are as follows: Hypotheses I: The abundance and diversity of arthropods, coupled with elevation, will affect litter decomposition rates.
Hypothesis II: The chemical composition of leaf litter will affect patterns of arthropod diversity and litter decomposition rates.
Hypothesis III: Litter decomposition rates will be enhanced for leaves in their home environment relative to other environments (home-field advantage).