Conservation and Quantitative Methods Flashcards
pseudoreplication
The use of inferential statistics to test for treatment effects with data from experiments where either treatment are not replicated (though samples may be) or replicates are not statistically independent.
types of pseudoreplication
simple, sacrificial, and temporal
simple pseudoreplication
samples are grouped together in a way that creates nonrandom differences between groups that don’t include ‘treatment effects. For example, two separate plots where all experimental organisms are in one plot, and all control are in the other
sacrificial pseudoreplication
data is pooled prior to statistical analyses, OR two or more samples taken from each experimental unit are treated as independent replicates; variance between treatments exists, but is inappropriately mixed with variance within treatments when the replicates are pooled
temporal pseudoreplication
samples aren’t taken from experimental units (like in simple pseudoreplication) but sequentially, creating nonrandom differences between grouped samples; samples are taken from same individuals at different time points, and the different time points are treated as independent samples, when there will be correlations between them as they are from the same individual; repeated sampling of experimental units is appropriate, it is only that treating them as independent data points is inappropriate
evidence that climate change is occurring?
global temperature increases - 1 degree celsius surface temps since late 1800s, and 0.3 degrees celsius ocean temps since 1969 (Levitus, 2017) - current warming is occurring roughly 10 times faster than the average rate of warming after an ice age; ice cores showing history of temperatures; melting glaciers and ice sheets; satellites show us that snow cover is decreasing; sea levels rising - 20 cm in the past century; extreme weather events are increasing in frequency and intensity; ocean acidification has increased by 30%
evidence that climate change is human caused?
“Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact.” (IPCC); increasing greenhouse gases, especially carbon dioxide from the burning of fossil fuels (transportation, industrial/factories) as well as deforestation (which reduces CO2 sinks), but also methane (landfills, agriculture, and natural gas leaks), nitrous oxide (agriculture/fossil fuels/burning vegetation), and chlorofluorocarbons (refrigerants, solvents). These greenhouse gases trap the heat within the atmosphere, preventing it from dispersing at the rate it normally would.
Describe some of the effects of climate change on species distributions, community composition, and ecosystem function
extreme weather events/natural disasters (drought, wildfire, hurricane) increases species through ecosystems losses in a stochastic way, as well as changing community composition (shifting alpine bumble bee communities toward species who are better suited for warmer temperatures - Scharnhorst, et al, 2023) (plant communities in most ecoregions in North, Central and South America have experienced thermophilization over the past four decades - Feeley, 2020) and ecosystem function (kelp forests provide food and shelter for animals in the community, but also provide ecosystem services for humans, such as carbon sequestering, reduce the force of storm-driven tides and surges and act like a trash fence to help retain nearshore sand, preventing erosion, but are declining due to increased ocean temperatures and acidification - Smale, 2019); range shifts (a meta-analysis of 764 species (mostly arthropods) found an average rate of poleward migration of 16.9 km/decade - Chen et al 2011); phenology mismatches
How could climate change influence evolutionary processes?
Evolutionary adaptation can be rapid and potentially help species counter stressful conditions or realize ecological opportunities arising from climate change; natural selection - changing or increasing selective pressures; gene flow - increasing or decreasing as species shift ranges; genetic drift - if populations become smaller or isolated due to die-offs or dispersal, would affect them more
paleontological example of climate change influencing evolutionary processes
(Simoes, 2022) time tree for the early evolution of reptiles and their closest relatives to reconstruct how the Permian-Triassic climatic crises shaped their long-term evolutionary trajectory. By combining rates of phenotypic evolution, mode of selection, body size, and global temperature data, we reveal an intimate association between reptile evolutionary dynamics and climate change in the deep past. We show that the origin and phenotypic radiation of reptiles was not solely driven by ecological opportunity following the end-Permian extinction as previously thought but also the result of multiple adaptive responses to climatic shifts spanning 57 million years. a strongly directional evolutionary regime by archelosaurs at the end of the Permian is associated with an adaptive response to those fast climatic shifts. ombined with ecological opportunity arising from the demise of several groups of early synapsids after the EGE and PTE (13, 14, 17, 18), climate change–driven adaptive evolution resulted in the rapid diversification of the vast diversity of reptile morphotypes that came to characterize worldwide ecosystems later on during the Triassic. Smaller body sizes favored (smaller area-volume ratios make them better capable of heat exchange with the surrounding environment). accelerated rates of morphological evolution among large-bodied archosauromorph reptiles, invasion of the marine realm by ichthyosauromorphs and sauropterygians, as well as maintenance of a small-bodied morphotype in lepidosauromorphs.
contemporary example of climate change influencing evolutionary processes
Brassica rapa blooms nearly 2 days earlier than pre-drought plants in response to a multi-year drought caused by climate change (Franks, 2007). One of the best examples of plant evolutionary response to an extreme climatic event comes from a resurrection study of the annual field mustard Brassica rapa [42,60]. The investigators collected a large sample of seeds from two California populations in 1997, after several wet years, and again in 2004 after several years of severe spring drought. They then grew population samples of genotypes collected in 1997 and in 2004 together in a common garden. The 2004 genotypes flowered significantly earlier in the common garden than the 1997 genotypes. Experimental water manipulations showed that early drought onset strongly selected for earlier flowering, evidence that the observed evolutionary change was adaptive. These B. rapa populations also display a genomic signature of temporal drought adaptation [42]. A genome-wide scan for Fst outlier-loci found 855 genes with significant temporal differentiation in allele frequencies between the 1997 and 2004 samples. Many had annotations suggesting involvement in flowering time and drought response. However, only 11 genes exhibited parallel shifts in allele frequencies in both populations. Thus, rapid adaptation to drought in the two populations appears to have occurred along largely independent trajectories.
Pros and cons of conserving ecological and evolutionary processes, rather than preserving of specific phenotypic variants - Moritz (1999)
Can still help individual species, but focusing more on overall eco and evo processes until extinction rates begin to decline; gene flow (via connecting fragmented habitats) helps populations, especially small ones; increase genetic diversity; certain phenotypic variants may be well suited for their current environment, but if they don’t have sufficient underlying genetic diversity, they will not be able to adapt to environmental changes; however, may lose certain species that are needed, like keystone species, if they aren’t given enough individual attention
fixed effects
variables that are constant across individuals; these variables don’t change or change at a constant rate over time; species, feather color, sex
random effects
variables that vary across individuals; colony, site; random effects allow us to control for noise caused by randomly chosen populations; Interested in effect size, not as much in its variation; random intercept or random slope
mixed model
mixed effects model is a type of regression model that combines both fixed and random effects. Mixed effects models are useful when there is variation in the effect of a factor across groups or individuals, but some of the variation is systematic (i.e., can be explained by specific variables) and some is random (i.e., cannot be explained by specific variables).
replication
repetition of an experiment or observation in the same or similar conditions. Replication is important because it adds information about the reliability of the conclusions or estimates to be drawn from the data.
pseudoissue
“those who do not see any problems with reducing spatial and temporal scales in order to obtain replication, and those who understand that experiments must be conducted in spatial and temporal scales relevant for the predictions to be tested, and replicate the experiment as well as possible within this constraint” = sometimes the constraints we work in make true replication impossible, or the more ideal approach is to include pseudoreplication; understand, be aware, avoid in experimental design when possible, and correct for it with models and analysis
pros of observational studies
naturally occurring and not manipulated by the researcher, so the results could be considered more realistic. Observational studies can also allow a researcher to gather a more broad set of information, not limited to the narrow scope of an experiment. Non-scientists can contribute to large observational datasets via “citizen science” efforts. Observational studies can also be done in situations where experiments are not possible, such as across large temporal or spatial scales; more generalizable across contexts
cons of observational studies
results of observational studies could be considered less reliable, as the variables are not directly controlled and manipulated; however, I would argue that a well-planned observational study is just as reliable as an experiment. Observational studies are limited in that a specific question can only be asked if it naturally occurs
pros of experimental studies
control for nearly all possible variables, often leading to more confidence in the results, can also be designed to explore a specific question
cons of experimental studies
can be challenging and expensive, and are not possible in every situation. Experiments, especially in ecology, lead to very specific results that are often not applicable to broader questions; not always natural or realistic; missing ecological context of species interactions, ecosystem effects, etc.
experimental studies
researcher manipulates the conditions or treatments the subjects receive in a controlled and randomized way
observational studies
researcher observes the effects of naturally occurring conditions or treatments, without manipulating them
Are the data treated in the same way for experiments vs observational studies (i.e. will the same statistical analyses be applied)?
A key goal for most research ventures is determining causality, which is done by statistical analysis. Ultimately, determining causality differs in experiments compared to observational studies. In experiments, determining causality is often simpler. Or, as put by Paul Holland (1986), “it is not that I believe an experiment is the only proper setting for discussing causality, but I do feel that an experiment is the simplest such setting.” In observational studies, causality is not as simple. However, using correlations, causation can be inferred - in some cases, correlation DOES mean causation. Causality can be determined by coefficients of correlation between variables (Simon, 1954).; observational studies will have a ton of variables, sources of error, and more complex models
natural experiments
individuals are exposed to the experimental and control conditions that are determined by nature or by other factors outside the control of the investigators. The process governing the exposures arguably resembles random assignment.; no manipulative control, but you can still examine the effects of a certain variable; example: after the clear-cutting of a section of the forest, you could compare the community composition between clear cut and control
under what conditions does it become essential to design an experiment to manipulate behavior?
When the question can no longer be answered by observation alone; for example, it is possible to observe bee behavior, and learn what they forage on by observation. You may notice the bees forage on citrus flowers, and you know that citrus flowers have caffeine in them. How does the caffeine affect their behavior? Does it make them move more/faster, learn better, get sick, change their taste perception, etc.? That must be done by experiment. Both approaches were necessary, because we didn’t know bees consumed caffeine until we saw them do it in nature.
ASA p-values statement
- P-values can indicate how incompatible the data are with a specified statistical model.
- P-values do not measure the probability that the studied hypothesis is true, or the probability that the data were produced by random chance alone.
- Scientific conclusions and business or policy decisions should not be based only on whether a p-value passes a specific threshold.
- Proper inference requires full reporting and transparency.
- A p-value, or statistical significance, does not measure the size of an effect or the importance of a result.
- By itself, a p-value does not provide a good measure of evidence regarding a model or hypothesis.
controversy over the use of p-values
“the ASA has not previously taken positions on specific matters of statistical practice”
summarize the proper use of p-values within a broader summary discussion of other methods for model and variable selection
“First, you can augment your p-value with information about how confident you are in it, how likely it is that you will get a similar p-value in a replicate study, or the probability that a statistically significant finding is in fact a false positive. Second, you can enhance the information provided by frequentist statistics with a focus on effect sizes and a quantified confidence that those effect sizes are accurate. Third, you can augment or substitute p-values with the Bayes factor to inform on the relative levels of evidence for the null and alternative hypotheses; this approach is particularly appropriate for studies where you wish to keep collecting data until clear evidence for or against your hypothesis has accrued. Finally, specifically where you are using multiple variables to predict an outcome through model building, Akaike information criteria can take the place of the p-value, providing quantified information on what model is best.” (Halsey, 2019)
Similarities between Bayesian and frequentist methods
Both are statistical methods used to estimate parameters and can be used for analysis or prediction. They both rely on the likelihood (the product of the probability of the data given the parameters), but in very different ways
frequentist statistics
a type of statistical inference that draws conclusions from sample data by emphasizing the frequency or proportion of the data
bayesian statistics
an approach to data analysis and parameter estimation based on Bayes’ theorem. Unique for Bayesian statistics is that all observed and unobserved parameters in a statistical model are given a joint probability distribution, termed the prior and data distributions.; actually been around longer than frequentist statistics, but only somewhat recently gaining popularity
Differences between bayesian and frequentist
bayesian: combination of prior data with new data to provide a “posterior,” or probability distribution - frequentist does not do this; in bayesian methods, the posterior distribution actually provides the probability of the outcomes, which is more intuitive and is not done in frequentist methods. Frequentist statistics estimates the desired confidence percentage (usually 95%) that some parameter occurs.; frequentist statistics accepts or rejects the null hypotheses, but Bayesian statistics estimates the ratio of probabilities of two different hypotheses.; “Frequentist statistics never uses or calculates the probability of the hypothesis, while Bayesian uses probabilities of data and probabilities of both hypothesis. Frequentist methods do not demand construction of a prior and depend on the probabilities of observed and unobserved data. On the other hand, Bayesian methods depend on a prior and on the probability of the observed data”; in frequentist, P-values are used to test for the probability of obtaining a test result at least as extreme as the result actually observed under the assumption of the null hypothesis; bayesian methods are generally more computationally complex (often require Markov chain Monte Carlo methods) than frequentist models
Bayes’ theorem
describes the probability of an event occurrence based on previous knowledge of the conditions associated with this event
For what purposes are Bayesian vs frequentist well suited?
more complex studies/models, or small dataset (priors help fill in), bayesian better. If you have no priors, frequentist better
statistical randomness
contains no recognizable patterns or regularities; sequences such as the results of an ideal dice roll or the digits of π exhibit statistical randomness
randomness vs chaos
random=boundaries, chaos=no boundaries