Trait-based approaches are useful in ecological research because of their potential ability to predict species responses from patterns present in the community and to infer mechanisms driving community assembly. Current approaches for fishes are lacking traits across all five fundamental niche dimensions (i.e. habitat, life history, trophic, metabolic and defense). This study quantified a broad range of fish functional traits across all five niche dimensions (commonly used traits and novel traits), quantified intra- and interspecific variation for each trait, tested for relationships among traits within and among niche dimensions, tested for phylogenetic conservatism of traits and assessed trait-environment relationships for a subset of these traits under two different contexts. Approximately one third of the quantified traits exhibited greater intraspecific variation than interspecific variation and were not included in subsequent analyses. There were similarities between phylogeny and trait dendrograms for all traits, and habitat, metabolic and defense traits. The traits identified in chapter 2 were able to explain species responses during different flow periods in two intermittent streams as well as species-specific differences in host microbiome at the onset of drought in one intermittent stream. The novel traits identified in chapter 2 did contribute to our understanding of the community assembly dynamics in chapter 3.

archives@tulane.edu / 1 / Peter Tellez

Climate change is expected to disproportionately impact high elevation ecosystems by disrupting current temperature and precipitation regimes. The future carbon balance of these systems is uncertain, given the interplay between longer growing season length and the potential for increased drought. Currently, the most robust inferences about ecosystem responses to changing climate come from the integration of experimental and observational methods. In this thesis, I utilize evidence from a warming experiment and an elevational gradient to gain insights into how aspects of ecosystem productivity and community functional composition change in response to the abiotic environment. First, I show that ecosystem productivity was similar in the heated and ambient treatment groups of the warming experiment. Net ecosystem productivity (NEP) was similar between treatments with only slightly increased NEP in the early season in the heated treatment. Important leaf functional traits (leaf mass per area, LMA; leaf dry matter content, LDMC) shifted with heating in directions associated with higher productivity, both at the community level and within species. While these results are counterintuitive, potential insight was provided by a soil cooling effect found in the heated plots in the early season. Second, I investigate ecosystem productivity across spatial and temporal gradients using phenology cameras. I show strong relationships between greenness indices generated from camera images and on-the-ground measurements of gross primary productivity (GPP). I also used changes in greenness indices early season to infer green-up rates, and found a strong pattern of increasing green-up rate with increasing elevation. Together, these studies highlight the importance of comparing experimental and gradient methods to assess how different spatial and temporal scales influence our conclusions about the effect of climate change on ecosystems.

Populations in fragmented habitat patches may show ecological differentiation, which has implications for metapopulation viability. In this study we used a common garden with two watering treatments to contrast mean differences in ecophysiological traits and the relationships between traits and performance among seven populations of three alvar species. These species differ in their alvar specialization in Ontario, from almost endemic (Solidago ptarmicoides) to highly confined (Dasiphora fruticosa) to a widespread generalist (Hypericum perforatum). Populations of all species exhibited mean differences in at least one trait: photosynthesis (Amax), growth rate and specific leaf area. More surprisingly, the relationship between functional traits and performance was significantly different among populations in all species, suggesting different strategies for maximizing growth in different environments. The ecological differentiation observed affected all species regardless of distribution and is likely genetically based. This differentiation may destabilize metapopulation dynamics and reduce rates of spread if colonization is negatively impacted.

Populations in fragmented habitat patches may show ecological differentiation, which has implications for metapopulation viability. In this study we used a common garden with two watering treatments to contrast mean differences in ecophysiological traits and the relationships between traits and performance among seven populations of three alvar species. These species differ in their alvar specialization in Ontario, from almost endemic (Solidago ptarmicoides) to highly confined (Dasiphora fruticosa) to a widespread generalist (Hypericum perforatum). Populations of all species exhibited mean differences in at least one trait: photosynthesis (Amax), growth rate and specific leaf area. More surprisingly, the relationship between functional traits and performance was significantly different among populations in all species, suggesting different strategies for maximizing growth in different environments. The ecological differentiation observed affected all species regardless of distribution and is likely genetically based. This differentiation may destabilize metapopulation dynamics and reduce rates of spread if colonization is negatively impacted.

<p>Species invasions are more prevalent than ever before. While the addition of a species can dramatically change critical ecosystem processes, factors that mediate the direction and magnitude of those impacts have received less attention. A better understanding of the factors that mediate invasion impacts on ecosystem functioning is needed in order to target which exotic species will be most harmful and which systems are most vulnerable. The role of invasion on nitrogen (N) cycling is particularly important since N cycling controls ecosystem services that provision human health, e.g. nutrient retention and water quality.</p><p>We conducted a meta-analysis and in-depth studies focused on the invasive grass species, Microstegium vimineum, to better understand how (i) plant characteristics, (ii) invader abundance and neighbor identity, and (iii) environmental conditions mediate the impacts of invasion on N pools and fluxes. The results of our global meta-analysis support the concept that invasive species and reference community traits such as leaf %N and leaf C:N are useful for understanding invasion impacts on soil N cycling, but that trait dissimilarities between invaded and reference communities are most informative. Regarding the in-depth studies of Microstegium, we did not find evidence to suggest that invasion increases net nitrification as other studies have shown. Instead, we found that an interaction between its abundance and the neighboring plant identify were important for determining soil nitrate concentrations and net nitrification rates in the greenhouse. In field, we found that variability in environmental conditions mediated the impact of Microstegium invasion on soil N pools and fluxes, primarily net ammonification, between sites through direct, indirect, and interactive pathways. Notably, we detected a scenario in which forest openness has a negative direct effect and indirect positive effect on ammonification in sites with high soil moisture and organic matter. Collectively, our findings suggest that dissimilarity in plant community traits, neighbor identity, and environmental conditions can be important drivers of invasion impacts on ecosystem N cycling and should be considered when evaluating the ecosystem impacts of invasive species across heterogeneous landscapes.</p> / Dissertation

I studied the community of lianas in the Yasuní Forest Dynamics Plot (YFDP), in Amazonian Ecuador. I found that species diversity of lianas in valley habitat was higher than in ridge habitat, but liana abundance was similar. I also found that community structure (species composition and their abundances) of lianas in ridge was distinct from that in valley because of the differential distribution and abundance of certain species along the topographic gradient. In an attempt to explain this phenomenon deterministically, I took two approaches: (1) to explore if trait expression of leaf-based traits, wood specific gravity and stem growth rate was different among species with ridge habitat association, species with valley habitat association, and generalist species; and (2) to explore if frequencies of different whole-plant growth strategies in the forest understory—defined by whether a liana was free-standing or already climbing, by its climbing mechanism, and by its understory appearance—were different between ridge and valley. My underlying rationale was that if certain trait expression or understory growth strategy can be associated to a given species, or group of species, and such species also drive the community structure difference between ridge and valley, then ecological insight on the biological deterministic mechanisms driving the difference can be gained. I end this one-page dissertation abstract right here and purposely leave you, the reader, perplexed—I invite you to seek answers to the liana distribution conundrum in the YFDP by perusing this dissertation.

As global change alters the chemical and physical dynamics of the ocean, it is increasingly necessary to determine ecological responses across environmental gradients. The benthic ecosystems of fjords often contain a multitude of environmental gradients conducive to multivariate field studies. In this thesis, I describe the benthic community structure of two British Columbian fjords in relation to markedly different environmental variables. In Chapter 2, I show a strong correlation between suspension-feeder abundance and flow structure on the steep fjord walls of Douglas Channel, BC. I also describe distinct assemblages with depth and with location along the fjord head-mouth axis. Using a suite of biological traits, I show that the deep portion (> 400 m depth) of the most seaward site is the most taxonomically and functionally diverse in the fjord. My results suggest fjord walls form an expansive ecosystem containing diverse and dense assemblages of suspension feeders relevant to the flow of energy through fjord basins and as biodiversity reservoirs. In Chapter 3, I extend a long-term hypoxia time-series (2006 -2016) to document the response of soft-bottom epibenthic megafauna of Saanich Inlet, BC to a prolonged hypoxic event in 2016 that caused abundance declines, community aggregation and shifts in species composition more extreme than those seen in the 2013 hypoxia cycle. I also assess community threshold responses along the oxygen gradient; I found community transitions consistent across years and with Northeast Pacific oxygen thresholds based in ecophysiological studies. Taken together, these studies show a strong coupling between oceanographic conditions and the community structure of fjord benthos. I suggest that climate-driven alterations in North Pacific oceanographic regimes may portend major changes in fjord ecosystems. / Graduate

In this research, I explore the changes in the functional diversity of herbivorous fishes in zones of coral reefs with different benthic composition: a zone dominated by corals, a zone dominated by algae and a transition zone in between the previous two. I choose to use functional traits which explain the feeding mechanics of this group of fish, as well their feeding rates and their previously established functional groups to understand how different assemblages of this fishes could affect their environment in different ways. I found clear differences in the functional diversity by calculating five indexes, functional dispersion (FDis), functional richness (FRic), functional divergence (FDiv), functional evenness (FEve) and functional specialization (FSpe). Each zone showed different species composition with different abundances; both parameters contribute to obtaining different values of the indexes. The coral-dominated zone showed the biggest multidimensional functional trait space (MFTS) with a value of FRic equals to 1 which means that its assemblage occupies 100% of the MFTS, while the transition zone assemblage occupied 83% and the algae-dominated zone occupied 16% of it. Thanks to this index I identified three functionally redundant species in the coral-dominated and the transition zones. The algae-dominated zone showed the lower FDis explained by the high abundance of grazers individuals. FDiv did not vary significantly between the three zones. FEve was higher in the algae-dominated zone; the index value decreased in the transition and coral-dominated zones, a similar tendency was shown by FSpe. Finally, to explore the importance of including functional diversity I made a comparison between the taxonomic and functional β-diversity. This research showed close relations of herbivorous fishes with their environment, but I could not establish if the benthic composition shapes the herbivorous fish assemblage or the other way around. This research can be a baseline to start working in functional diversity in the Red Sea coral reefs, can help to understand what to expect in the evaluation of reefs in different health state and to identify which herbivorous fish species or groups are more vulnerable and more important according to their function for coral reefs.

Weed seed contaminants in agricultural products from China in recent years have the potential for introducing new invasive plant species. Seeds of 169 weedy species from 39 families were collected from Chinese farmlands. Fifty-eight of these that are currently absent in Canada were evaluated. Two weed risk assessment (WRA) models (modified WRA+ secondary screen tool and weed elsewhere+ modified WRA+ secondary screen tool) rejected all invasive plant species and showed similar accuracy in non-invasvie plant species prediction based on 140 existing alien plant species in Canada, yet the second WRA model took significantly less time to conduct the evaluation. Fifty-five potential invasive species with various negative impacts in Chinese farmlands were rejected to enter Canada by the “weed elsewhere+ modified WRA+ secondary screen tool” model, including eight species that cause significant damage to Chinese farmlands. However, Anemone rivularis and Silene jenisseensis, which have no negative impacts in China, were also rejected. Seed germination characteristics among 18 Chinese weedy species were found with base temperatures for germination (Tb) varying from -2.5°C to 10.9°C, thermal time requirements to reach 50% germination (θ_50) ranging from 23.7 to 209.2℃*Day, and different optimal temperatures for germination, which may facilitate these species to cause different degrees of negative impacts in Canadian prairie provinces. An alien species would have a higher competitive advantage in resource uptake and space occupation than its congeneric with advantageous seed germination characteristics; otherwise it will be less competitive than its congeneric. In addition, plant functional traits that promote invasiveness would make an alien species more invasive. In conclusion, the “weed elsewhere+ modified WRA+ secondary screen tool” model is a fast and highly accurate way to screen out potential invasive species from Chinese environments, and is applicable to other environments with modification. Seed germination characteristics can be used to predict seasonal dynamics of weed seedling populations. The comparison of seed germination characteristics and other plant functional traits between alien plant and its congeneric weed from native areas provides a new way to evaluate the invasive potential of alien plant species.