Ecology. Michael Begon

Скачать книгу

−0.86 0.20 106 1.000 0.137 5 67 0.087 0.030 0.343 1.826 −1.06 0.18 75 1.122 0.098 6 44 0.057 0.017 0.295 1.643 −1.24 0.15 45 1.020 0.058 7 31 0.040 0.012 0.290 1.491 −1.40 0.15 34 1.093 0.044 8 22 0.029 0.013 0.455 1.342 −1.55 0.26 37 1.680 0.049 9 12 0.016 0.006 0.417 1.079 −1.81 0.23 16 1.336 0.021 10 7 0.009 0.005 0.571 0.845 −2.04 0.37 9 1.286 0.012 11 3 0.004 0.001 0.333 0,477 −2.41 0.18 0 0.000 0.000 12 2 0.003 0.000 0.000 0.301 −2.59 0.00 0 0.000 0.000 13 2 0.003 0.000 0.000 0.301 −2.59 0.00 0 0.000 0.000 14 2 0.003 0.001 0.500 0.301 −2.59 0.30 0 0.000 0.000 15 1 0.001 0.000 −2.89 0 0.000 0.000 Total

      the columns of a life table

      The first column in each life table is a list of the stages or age classes of the organism’s life. For Gilia, these are simply the stages ‘seed’, ‘emerged plants’, and ‘flowering plants’. For the marmots, they are years. The second column is then the raw data from each study, collected in the field. It reports the number of individuals surviving to the beginning of each stage or age class (see Figure 4.9). We refer to these numbers as a_x, where the x in the subscript refers to the stage or age class concerned: a₀ means the numbers in the initial age class, and so on.

Ecologists are typically interested not just in examining populations in isolation but in comparing the dynamics of two or more perhaps rather different populations. This was precisely the case for the Gilia populations in Table 4.1. Hence, it is necessary to standardise the raw data so that comparisons can be made. This is done in the third column of the table, which is said to contain l_x values, where l_x is defined as the proportion of the original cohort surviving to the start of age class. The first value in this column, l₀ (spoken: L‐zero), is therefore the proportion surviving to the beginning of this original age class. Obviously, in Tables 4.1 and 4.2, and in every life table, l₀ is 1.00 (the whole cohort is there at the start). Thereafter, in the marmots for example, there were 773 females observed in this youngest age class. The l_x values for subsequent age classes are therefore expressed as proportions of this number. Only 420 individuals survived to reach their second year (age class 1: between one and two years of age). Thus, in Table 4.2, the second value in the third column, l₁, is the proportion 420/773 = 0.543 (that is, only 0.543 or 54.3% of the original cohort survived this first step). In the next row, l₂ = 208/773 = 0.269, and so on. For Gilia (

Скачать книгу