schoener             package:adehabitat             R Documentation

_C_o_m_p_u_t_e _S_c_h_o_e_n_e_r'_s _r_a_t_i_o

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

     'schoener' computes the Schoener's ratio on radio-tracking data.
      'schoener.rtest' performs a randomization test of the equality of
     the Schoener's ratio to 2

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

     schoener(tr, keep, byburst = TRUE)
     schoener.rtest(tr, keep, byburst = TRUE, nrep = 500)

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

      tr: an object of class 'traj' 

    keep: a vector of length 2, giving the lower and the upper bound of
          the time interval for which a pair of relocations is
          considered in the computation of t\^2 (see details).  These
          values are given in seconds.

 byburst: logical.  If 'TRUE', the Schoener's ratio is computed by
          burst.  If 'FALSE', the ratio is computed by animal.

    nrep: the number of randomisations of the test. 

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

     The Schoener's ratio is a measure of time-autocorrelation in the
     data. This ratio is computed as the squared mean distance between
     "neighbour" relocations (t\^2) divided by the squared mean
     distance between the relocations and their barycenter (r\^2).  The
     theoretical value of this ratio under the hypothesis of
     independance of the relocations is 2.

     Swihart and Slade (1985) consider as neighbour two successive
     relocations.  However, the Schoener's ratio computed in this way
     makes sense biologically only if the relocations are equally
     spaced in time.  However, as indicated by these authors, "such a
     data set probably is the exception rather than the rule because
     many problems may arise in taking a locational reading at a
     specified time".

     In this function, we define as "neighbour" two relocations (not
     necessarily successive relocations) separated by a time interval
     comprised within the bounds specified in the vector 'keep' (in
     seconds).  For example, if 'keep = c(60, 300)', all relocations
     separated by a time interval comprised between 1 and 5 minutes are
     considered in the computation.  Thus, the total number of pairs of
     relocations m taken into account in the computation may be larger
     than the number of relocations n (m can be at most equal to
     n*(n-1)/2).

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

     returns an object of class 'schoener'.

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

     Clment Calenge calenge@biomserv.univ-lyon1.fr

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

     Swihart, R.K. and Slade, N.A. (1985) Testing for independence of
     observations in animal movements. _Ecology_, *66*, 1176-1184.

     Schoener, T.W. (1981) An empirically based estimate of home range.
     _Theoretical Population Biology_, *20*, 281-325.

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

     data(puechcirc)
     puechcirc$date[1:10]

     ## Relocations are taken every 10 minutes
     ## For example we consider relocations as
     ## neighbour when they are separated by a time
     ## interval comprised between 5 and 15 minutes
     schoener(puechcirc, keep = c(5*60, 15*60))
     ## Not run: 
     schoener.rtest(puechcirc, keep = c(5*60, 15*60))
     ## End(Not run)

