Introduction to Multivariate Analysis

Chatfield, Christopher; Collins, Alexander J.

doi:10.1201/9780203749999

Cited by 189 publications

(182 citation statements)

References 0 publications

Supporting

Mentioning

166

Contrasting

Unclassified

Order By: Relevance

“…In the principal components analysis of the seven explanatory variables, three components had eigenvalues in excess of unity and explained 50, 21 and 18% of the variation in the data, respectively. These three axes were subsequently rotated with the varimax rotation (Chatfield & Collins, ; Cooley & Lohnes, ).…”

Section: Resultsmentioning

confidence: 99%

Determinants of some leaf characteristics of Australian mangroves

Saenger

West

2016

Bot. J. Linn. Soc.

View full text Add to dashboard Cite

Leaf characteristics reflecting the size, lifespan (longevity), moisture content (degree of succulence) and complexity of structure of 20 mangrove species were studied over several years at 13 locations along the tropical and subtropical Australian coast. These characteristics were found to fall generally within the ranges of those for woody species from other ecosystems. With the exception of one species, it was found that leaf longevity was related inversely to leaf moisture content, increasing from nearly 6 months in more succulent species to over 2 years in less succulent species. This suggested that more succulent leaves are less complex in their structure because they have less well-developed ability to compartmentalize salt. There was a tendency also for leaf longevity to increase in species with larger leaves. These findings were consistent with the general view for land plants that leaf longevity is greater in species that have developed tolerance to environmental stress, salt particularly in the case of mangroves. Leaf tissue in such species is more robust or complex and requires greater metabolic resources in its construction; the plant is then advantaged by retaining the tissue for longer periods. Classification of the species considered here, based on their leaf longevity, moisture content and complexity, identified phylogenetically related species groupings that reflected these leaf longevity effects.

show abstract

Section: Resultsmentioning

confidence: 99%

Determinants of some leaf characteristics of Australian mangroves

Saenger

West

2016

Bot. J. Linn. Soc.

View full text Add to dashboard Cite

show abstract

“…In our work, the Spearman’s rank correlation is specifically used to assess the association between biogeochemical markers like dissolved oxygen and nitrate and hydrologic indicators such as hydraulic gradient, specific conductivity, and temperature. A Spearman’s rank correlation matrix [ Chatfield , 2018] is created to summarized these relationships.…”

Section: Methodsmentioning

confidence: 99%

Dissolved oxygen dynamics reveal biogeochemical tipping points driven by river corridor hydrology

Kaufman

Ghosh

Grate

et al. 2020

Preprint

View full text Add to dashboard Cite

Riverbeds can have an important impact on large-scale fluxes of biogeochemically active solutes in river corridor systems. The hyporheic zone is an important area of both hydrology and biogeochemistry, particularly in a hydropeaked river system where rapid variations in river stage height, hydraulic gradients, and residence times occur. We measured several biogeochemical and hydrological parameters at three different subsurface depths in the riverbed of the Columbia River in Washington state, a complex hydropeaked river system with significant subsurface heterogeneity. During the study, episodes of significant dissolved oxygen (DO) change were observed. The DO signal changes were the most apparent, compared to more modest changes in other biogeochemical markers. While DO is often associated with biological activity, we ultimately found that the notable DO excursions were associated with hydrologic gradients. Here we describe hydrologic perturbations and biogeochemical responses in terms of hydrobiogeochemical regimes. Two different forms of DO response to hydraulic gradient perturbation were observed, defining different hydrobiogeochemical regimes. The system tips abruptly from one regime to the other, exhibiting threshold behavior that is uncaptured in current estimations of cumulative influences of subsurface processes from reach to earth system scales.Plain language summaryThe water in a river is constantly flowing in and out of the river’s bed. While it is in the bed, microbes process environmentally and ecologically important nutrients and other compounds. The exchange of water between the river and the riverbed is largely controlled by the stage of the river. Many processes, both natural and human, can cause rapid changes in the river stage. These rapid stage changes can cause abrupt changes in the riverbed’s ability to process nutrients and other compounds. In this study, we use dissolved oxygen as a window into riverbed microbial and chemical processing. We see that relatively rapid changes in river stage can cause abrupt changes in the concentrations of chemicals in the riverbed, indicating fundamental changes in how the riverbed processes are occurring. Understanding these abrupt and fundamental changes is important to our overall understanding of the ecological function of river corridor systems.3 key pointsA hydrobiogeochemical regime is defined by the functional form of the relationship of a hydrologic perturbation and biogeochemical marker.Short-term hydrologic perturbations drive tipping points between distinct hydrobiogeochemical regimes.Linear and hysteretic dissolved oxygen dynamics define distinct regimes as observed throughout the hyporheic zone.

show abstract

“…). Principal components analysis (PCA: Chatfield and Collins ) was then used on transformed variables, normalized to have a mean of zero and a standard deviation of one, as a data reduction technique to identity orthogonal factors and the variables that loaded highly in each factor. We performed a nonmetric, multivariate, multidimensional scaling (NMDS: Kruskal and Wish , R package vegan v2.3‐1; Oksanen et al.…”

Section: Methodsmentioning

confidence: 99%

Negative impacts of invasive plants on conservation of sensitive desert wildlife

et al. 2016

View full text Add to dashboard Cite

Abstract.Habitat disturbance from development, resource extraction, off-road vehicle use, and energy development ranks highly among threats to desert systems worldwide. In the Mojave Desert, United States, these disturbances have promoted the establishment of nonnative plants, so that native grasses and forbs are now intermixed with, or have been replaced by invasive, nonnative Mediterranean grasses. This shift in plant composition has altered food availability for Mojave Desert tortoises (Gopherus agassizii), a federally listed species. We hypothesized that this change in forage would negatively influence the physiological ecology, immune competence, and health of neonatal and yearling tortoises. To test this, we monitored the effects of diet on growth, body condition, immunological responses (measured by gene transcription), and survival for 100 captive Mojave tortoises. Tortoises were assigned to one of five diets: native forbs, native grass, invasive grass, and native forbs combined with either the native or invasive grass. Tortoises eating native forbs had better body condition and immune functions, grew more, and had higher survival rates (>95%) than tortoises consuming any other diet. At the end of the experiment, 32% of individuals fed only native grass and 37% fed only invasive grass were found dead or removed from the experiment due to poor body conditions. In contrast, all tortoises fed either the native forb or combined native forb and native grass diets survived and were in good condition. Health and body condition quickly declined for tortoises fed only the native grass (Festuca octoflora) or invasive grass (Bromus rubens) with notable loss of fat and muscle mass and increased muscular atrophy. Bromus rubens seeds were found embedded in the oral mucosa and tongue in most individuals eating that diet, which led to mucosal inflammation. Genes indicative of physiological, immune, and metabolic functions were transcribed at lower levels for individuals fed B. rubens, indicating potential greater susceptibility to disease or other health-related problems. This study highlights the negative indirect effects of invasive grasses, such as red brome, in desert ecosystems, and provides definitive evidence of a larger negative consequence to health, survival, and ultimately population recruitment for Mojave Desert tortoises than previously understood.

show abstract

Introduction to Multivariate Analysis

Cited by 189 publications

References 0 publications

Determinants of some leaf characteristics of Australian mangroves

Determinants of some leaf characteristics of Australian mangroves

Dissolved oxygen dynamics reveal biogeochemical tipping points driven by river corridor hydrology

Negative impacts of invasive plants on conservation of sensitive desert wildlife

Contact Info

Product

Resources

About