dga                  package:labdsv                  R Documentation

_D_i_r_e_c_t _G_r_a_d_i_e_n_t _A_n_a_l_y_s_i_s

_D_e_s_c_r_i_p_t_i_o_n:

     Direct gradient analysis is a graphical representation of the
     abundance distribution of (typically) species along opposing
     environmental gradients

_U_s_a_g_e:

     dga(z,x,y,step=25,pres="+",abs="-",labcex=1,
         xlab = deparse(substitute(x)), ylab = deparse(substitute(y)),
         pch = 1, title = "", ...)

_A_r_g_u_m_e_n_t_s:

       z: the variable (typically a species abundance) to be plotted

       x: the variable to use as the x axis

       y: the variable to use as the y axis

    step: controls the grid density fed to the GAM surface fitter

    pres: the symbol to print when a species is present
          (presence/absence mode)

     abs: the symbol to print when a species is absent
          (presence/absence mode)

  labcex: the character size for contour labels

    xlab: the x axis legend

    ylab: the y axis legend

     pch: the symbol to print in continuous abundance plots

   title: the title to print

     ...: miscellaneous arguments to pass to par

_D_e_t_a_i_l_s:

     'dga' interpolates a grid of x,y values from the supplied data and
     fits a GAM (from 'mgcv') of the z variable to the grid.   The GAM
     surface is then represented by a contour map and abundance 
     symbols as described above.

_V_a_l_u_e:

     a graph of the distribution of the z variable on a grid of x and y
     is displayed

_N_o_t_e:

     Direct gradient analysis was promoted by Robert Whittaker and
     followers as a preferred method of vegetation analysis.

_A_u_t_h_o_r(_s):

     David W. Roberts droberts@montana.edu <URL:
     http://ecology.msu.montana.edu/droberts>

_R_e_f_e_r_e_n_c_e_s:

     <URL: http://ecology.msu.montana.edu/labdsv/R>

_S_e_e _A_l_s_o:

     'gam'

_E_x_a_m_p_l_e_s:

         data(bryceveg) # returns a data.frame called bryceveg
         x <- c(0.2,0.5,1.0,2.0,3.0,4.0,5.0,6.0)
         y <- c(0.2,0.5,3.0,15.0,37.5,62.5,85.0,97.5)
         cover <- vegtrans(bryceveg,x,y)
         data(brycesite)
         dga(round(cover$arcpat),brycesite$elev,brycesite$av)

