Ecology Practical I
In this course students are to acquire skills in the most frequently used research methods in the field of ecology. Students prepare for field practice beforehand, collect data in the field, evaluate these and submit a detailed report of their work.
I. Plant Ecology
1.) Assessement of forest canopy structure through light measurements By measuring the amount and spatial distribution of light penetrating the forest canopy allows the investigator to estimate the amount of current foliage in the forest canopy. The widely used Leaf Area Index (LAI) variable is determined in two deciduous forest stands of different density (i.e. one in a closed forest, the other in an open stand without canopy closure). Students compare the LAI values obtained in the two forests and with literature data. Routine calibration of light meters is also part of the measarement.
2.) Relationship between forest understorey species composition and light regime Plant species in forest understories may differ in their light requirements (or shade tolerance) thus their presence at a certain locality indicates local light regime on the forest floor. The purpose of this investigation is to search for relationship between light intensity and plant species distribution patterns on the forest floor. Following an appropriate sampling design numerous point samples are taken by measuring light intensity on the top of herbs and subsequent recording of plant species identities at the given locality. Students work in groups of two, then compile their data into a large common database containing the results of all groups. During evaluation students use this large database to statistically test for three species whether the spatial distribution of a given species is independent from that of light intensity.
3.) Estimation of plant ground cover Percentage canopy ground cover is a routinely used variable in vegetation science for the estimation of the amount of plants at a given locality (either per species, per canopy layers or for the vegetation as a whole). Precise estimation of cover needs long practice and inevitably contains subjective elements. Here students obtain skills in a simple yet highly objective technique to estimate plant cover based on a large number of spot observations. In a forest stand appropriately large (e.g. 30x30 m) sample quadrat is set up and along both diagonals in 0.5 m intervals students record binary data: presence or absence of plant cover (either per species or for overall foliage). Percentage ground cover values are calculated from presence frequencies in these binary database. A simple device (densiometer) helps students to confine their observations to a small spot at each diagonal interval. The whole measurement is repeated in two forest stands of different tree density. After the sample plot is set up in the vegetation students first judge canopy cover through simple observation (subjective method), then complete the measurement for more exact cover values (objective method). In the evaluation students compare the results from the two methods and calculate percentage error of estimation for the subjective methods in the two forests.
4.) Basic measures of forest stand structure: tree height and trunk diameter In forestry practice the two most commonly used measures of tree growth is height and trunk diameter. In forest ecological studies the frequency distributions of these two parameters are informative to stand structure and development. By using trigonometric functions students determine tree height from distance and angle of view to tree-top data, and measure trunk circumference in breast height by using tape measures. Two forest stands are compared by considering means and frequency distributions for both variables. From these data the timber volume (m3 ha-1) is also estimated and compared with literature values. 5.) Aspect preference of plant species in a region of varied topography In the varied landscape of the Northern Mezőföld region, Hungary steep slopes facing different azimuth direction often accomodate grasslands with different plant species composition. Students make a systematic survey part of the landscape following a preconfigured sampling design, record plant species occurrence and associated compass direction at a high number of localities. In the resulting database it is tested statistically if the experimental frequency distributions of slope aspect and plant species are independent.
6.) Shrub invasion in abandoned pastures on loess bedrock Grassy slopes in loess areas often support grasslands maintained by regular grazing or cutting. After abandonement succession commences towards forest development that usually starts with encroachment of shrubs. In such a newly formed shrubland students investigate the following questions: 1) Which shrub species take part most often in this successional change? 2) What propagule dispersal types (e.g. anemochory, zoochory, etc.) are the most frequent? 3) In one shrubland stand students test if there is one or more shrub size measure (e.g. shoot height, stem diameter) that can be used as an appropriate proxy for plant age. 4) In the same shrubland patch the age distribution of shrub populations is used to estimate the time of abandonement of pasture management. 5) Using the nearest neighbor method the spatial distribution pattern of the most abundant shrub population is determined.
7.) Determination of minimal area in forests In plant community ecology (and particularly in phytosociology) the minimal area is important methodological concept: it is the smallest ground area where 90% of the plant species in a plant association shows up, thus this is the smallest appropriate sample area for studying the given community. Depending on community type (from annual grasslands to aged forests) the minimal area can be widely different. Students determine the minimal area in two different deciduous forest stands by recording all species occurring in a series of sample units (quadrats) of increasing area.
8.) Association analysis: search for systamatic cooccurrence of plant species pairs Systematic coexistence of plant species in the field - as a phenomenon - may indicate similar ecological requirements (environmental tolerance). If sufficiently high number of sample units is examined, it is easy to test the independence of occurrence of species pairs. Students record plant species composition in a series of sample quadrats in the field, then prepare rectangular contingency tables and use Chi2 statistical tests of independence for species pairs.
9.) Comparison of species diversity and evenness in two forest communities In two forest stands of different disturbance history students record plant species composition and abundance (ground cover) in sample quadrats following an appropriate sampling design. From these data they calculate species number (S), Shannon-Weaver diversity (H) and Evenness (E) values, and compare these for the two forest stands and with literature values.
10.) Comparison of two habitats by using the tool of phytoindication Using the species compositon and abundance data obtained in the previous investigation (9) students render the Ellenberg ecological indicator values to each species, than calculate frequency distributions for each indicator value (T,W,R, etc.), and from these they qualify associated habitat abiotic environmental quality and compare these for the two comminity types.
11.) Visit to an ecological field research site Students have a guided visit to a field research site where they are introduced into ongoing ecological research work.
II. Animal Ecology
12.) Determination of population size Students determine the size of arthropod populations by using various sampling designs and methods to estimate population size: (a) transect record (in two 30 cm wide zones along both sides of a 20 m long transect students record all visually detectable arthropods (species identity and number of individuals) also considering distance perpendicular to the line). From these data they estimate the size of the whole arthropod population present on site. (b) knocking (the arthropod assemblage from indivudal shrubs is collected in this way); and (c) quadrate study (the abundance of arthopods is determined in 45x45 cm rectangular quadrats placed randomly in the field).
13.) Estimation of population size by using the mark-recapture method The mark-recapture method - as a key tool for population size estimation - is applied by using soil traps to assess the population size for arthropods living on the soil surface. For this purpose students place soil traps in two habitats markedly differing in spatial heterogeneity by using pre-determined grid size. Captured arthropods are marked, released and recaptured.14.) Island biogeography Students record colonization functions in the field, detect the area - species number power function by using a series of sample plots of increasing size. For this purpose students collect all arthropods from nested plots of logarithmically increasing size by means of three collection methods, then determine species number for each plot size .
Crawley, M.J. 1997: Plant Ecology. 2nd ed. Blackwell Science, Oxford.
Gibson, D.J. 2002: Methods in comparative plant population ecology. Oxford Univ. Press. Oxford
other information: for Section I. additional information is available on the web: http://ramet.elte.hu/~ramet/oktatas/novokolgy1.html