BIL 161: Introduction to Exploring Biodiversity

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1 BIL 161: Introduction to Exploring Biodiversity Biodiversity is defined as the degree of variation of living organisms within a particular ecosystem (or the entire planet). Your first research project is designed to introduce you to a naturalist s perspective of biodiversity. I. Biodiversity Biodiversity can be considered at various, hierarchical levels (Figure 1). In biological terms A species is a group of organisms able to interbreed in nature to produce fertile, viable offspring. A population is defined as all the individuals of the same species living in a defined region. A community is defined as all the populations living in a defined region. An ecosystem comprises the biotic (living) and abiotic (non-living) components of a defined region. A landscape comprises the patterns of and interactions between ecosystems within a region of interest. The biosphere comprises the regions on earth where life can exist. Exploring Biodiversity - 1 Figure 1. The ecological hierarchy, from individual organism to biosphere. The biodiversity of a specific ecosystem is determined by its abiotic factors. Every species (and population) evolves specific requirements and tolerance limits for such factors as temperature various nutrients etc. light various harmful chemicals humidity ph The evolution of populations within an ecosystem also can be affected by their own population s density interactions with other populations Within an ecosystem, microhabitats characterized by specific physical factors provide resources for species evolved to live within them. For example, pond ecosystem microhabitats could include empty gaps (interstices) between the living matter of plants areas under rocks and stones the open water column sediment at various depths the water surface Species composition and diversity varies with ecosystem and microhabitat conditions. Abiotic components determine the composition and abundance of biotic components. Biotic components, in turn, affect each other's abundance and diversity.

2 II. Measures of Biodiversity Ecologists use various indices to determine biodiversity within and among ecosystems. You will use two commonly employed measures, species richness and species abundance. A. Species Richness The simplest measure of an ecosystem s biodiversity is species richness (S), the number of different species found in a collected sample. Species richness does not take into account the abundance of each species, only their presence. Menhinick s Index (D) of species richness is the number of species in a sample divided by the square root of the number of individuals in the sample. In which: s = the number of different species in a sample N = the total number of individual organisms (all species) in the sample B. Species Abundance The abundance of a particular species in an ecosystem (or microhabitat) is simply the number of individuals in that ecosystem (or microhabitat). The relative abundance of a particular species in an ecosystem is a measure of how common or rare that species is in comparison to other species in the same ecosystem or microhabitat. The relative abundance of any given species is the number of individuals of that species divided by the total number of individuals of all species combined. For example, if you collected a one milliliter (ml) sample of pond water and found the following numbers of each of three species: 100 diatoms (Neidium pseudodensestriatum) 50 nematodes (Psilenchus hilarulus) 5 mosquito larvae (Aedes aegypti) 155 TOTAL INDIVIDUALS Then the relative abundance of each species would be: Neidium pseudodensestriatum: 100/155 = 0.64 Psilenchus hilarulus): 50/155 = 0.32 Aedes aegypti 5/155 = 0.03 You may encounter other measures of biodiversity in the literature search you will perform to prepare for this project. You may use them, if your team decides it is appropriate to do so. However, the measures above should serve you well for this project. Exploring Biodiversity - 2

3 III. The Nature of the Research Project Your team will NOT be manipulating an experimental system. There will be no treatment or control groups. The research project you are about to undertake is best classified as a survey. Your team will be collecting samples from two different, naturally occurring aquatic systems to measure and compare their relative biodiversities. For example, your team may decide to compare species richness between two systems compare abundance of particular species between two systems compare abundance of larger taxonomic groups between two systems insert your clever and relevant idea here You might wish to consider whether biodiversity differs between open vs. closed systems different tidal levels in the same system freshwater/brackish/marine systems habitats with different levels of fertilizer runoff small vs. large systems habitats with different levels of other pollutants different times of day in the same system insert your clever idea here, too. Your task will be to identify two local, naturally occurring aquatic habitats/microhabitats that you predict will have differences in some aspect of biodiversity for a specific, logical reason. There are many local aquatic environments from which your team can choose. Close to the center of campus lies brackish Lake Osceola. It is connected to the ocean by a long network of canals, so species from both freshwater and marine environments have access to the lake. The freshwater lake on the campus of Florida International University is another possible resource. Coral Gables and nearby communities are dotted with many man-made ponds and canals. Within driving distance of campus are accessible marine environments such as Matheson Hammock, Crandon Park, and other public coastal areas. Your research question is limited only by your imagination. Consider interesting, relevant possibilities, and use these as keywords in your literature search. IMPORTANT: Your survey project is a pilot study. A pilot study is a small scale, preliminary study conducted to evaluate a system prior to full-scale research. Each of the systems listed above has multiple environmental factors that could affect biodiversity. You may list differences between your systems and predict their possible effects. However, you will not be able to make a definitive statement about the reason for any observed difference in biodiversity between your systems without additional, controlled research. When your team prepares its final presentation, one of your most important points should be to describe further research that would help you to identify specific factors affecting the aspects of biodiversity you have examined. Exploring Biodiversity - 3

4 IV. Aquatic Environmental Factors and Biodiversity In this section you will learn to identify environmental some factors to consider when choosing two habitats to sample and compare. Remember that you will not be able to positively identify the factors responsible for any differences in biodiversity you observe without additional, controlled experiments. But this along with your literature search should help you devise a logical, informed overall hypothesis that can be translated into testable null and alternative experimental hypotheses. A. Homeostasis: Regulators and Conformers Homeostasis is the maintenance of constant internal (controlled) variables such as o temperature o ph o water content o ion concentrations o etc. Species differ in their ability to keep controlled variables distinct from external environmental conditions. Because an organism s reproductive success (the keystone of natural selection) is affected by its ability to meet environmental challenges, a species' ability to survive environmental extremes reflects its evolutionary history. A regulator metabolically maintains homeostasis in response to environmental changes. o A regulator can control the value of a particular controlled variable. A conformer is less able to metabolically maintain homeostasis in response to environmental changes. o The value of a conforming controlled variable is governed primarily by the external environment. A species may be a regulator with respect to some controlled variables, and a conformer with respect to others. (Figure 2) Figure 2. A salmon s body temperature varies with environmental temperature. It s chloride concentration, however, is controlled metabolically, and does not vary with environmental chloride concentration. Thus, the salmon is a thermoconformer and an osmoregulator. Exploring Biodiversity - 4

5 Note that even regulators have tolerance limits for various environmental factors. A mammal like you can metabolically control internal body temperature. But unprotected exposure to extreme temperatures can override homeostasis, with possibly dire consequences. When you design your experiment and analyze your results, consider whether the organisms in your systems are conformers or regulators with respect to various environmental factors, and what the tolerance limits for those environmental factors are for each species. B. Biotic and Abiotic Environmental Factors Different species have different tolerances to dissolved salts. Biodiveristy will differ among natural freshwater, brackish, and marine environments. But consider the implications of climate change. Southern Florida is predicted to be one of the geographic regions hardest hit by even small degrees of sea level rise. This will mean more than just flooding at high tide. Even when tides are low, salt water intrusion into freshwater aquifers may have a profound effect on species diversity. The most abundant dissolved ions in most aquatic habitats are sodium, chloride, magnesium, sulfate, and calcium. Marine water contains grams of salts per liter. Modern seawater is hyperosmotic with respect to a typical cell s cytosol. Most (not all) marine protists, plants, and invertebrates are osmoconformers. However, some marine organisms (e.g., bony fish) expend metabolic energy to retain water in the cytosol and remove ions. Fresh water is defined as having less than 0.5 grams dissolved salts per liter. Fresh water is hypoosmotic with respect to a typical cell s cytosol. Brackish water is defined as having between grams of dissolved salts per liter. This wide range means that the term brackish is rather imprecise. Tidal flow can cause wide fluctuations in salinity over the course of a day. Brackish ion fluctuations can present osmotic challenges to many types of organisms. C. Other Natural Abiotic Factors Aquatic habitats throughout southern Florida can vary in light level, temperature, chemical composition, and any number of other factors. These factors can vary not only among ecosystems, but within a system over the course of a day, month, or year. One difficulty faced by every ecologist is controlling for multiple variables. When you select the two systems you wish to compare, you and your team should list all possible differences between the two habitats that could affect biodiversity. Your team should be able to propose additional studies that would allow you to determine whether a particular factor affects biodiversity explain the physiological and cellular mechanism(s) responsible D. Anthropogenic Factors Anthropogenic (from the Greek anthropos (human) and genesis (origin)) factors are those generated by humans. Suburban areas are subjected to human disturbance such as pesticide and fertilizer runoff, physical disruption, sanitation/clearing efforts, etc. How might these factors affect species diversity and species composition of a nearby aquatic system? Consider various factors that might affect biodiversity, and use these as keywords in your literature search to find background information. Exploring Biodiversity - 5