ClearAll["Global`*"]

Needs["Graphics`PlotField`"]

\(myspdr[b_] := 
      Module[{x, dp, sp, gdpsp, sq, p, t, dt, fdt, 
          arrowx}, 
dp[x_] := 
          15 - b*x; 
sp[x_] := 
          1 + 1.0*x; 
gdpsp = 
          Plot[{dp[x], sp[x]}, {x, 0, 15}, 
            PlotStyle -> {{Hue[0.0]}, {Hue[0.6]}}, 
            DisplayFunction -> Identity]; 
sq[p_] := 
          Evaluate[
            x /. \(Solve[p == sp[x], 
                  x]\)[\([1]\)]]; 
p[0] = 
          5.5; 
dt = 
          Table[{{x[t] = sq[p[t]], p[t]}, {x[t + 1] = x[t], 
                p[t + 1] = dp[x[t + 1]]}}, {t, 0, 
              5}]; 
fdt = 
          Evaluate[Flatten[dt, 1]]; 
arrowx = 
          Graphics[
            Table[Arrow[fdt[\([i]\)], fdt[\([i + 1]\)], 
                HeadScaling -> Relative], {i, 1, 
                10}]]; 
Show[gdpsp, arrowx, 
          PlotRange -> {{0, 15}, {0, 15}}, 
          AxesLabel -> {"q", "p"}, 
AspectRatio -> 1]]\)

Show[myspdr[1.5], 
      PlotLabel -> "\:8718\:86db\:306e\:5de3\:8abf\:6574\:904e\:7a0b\n\
(|\:9700\:8981\:66f2\:7dda\:306e\:50be\:304d|>|\:4f9b\:7d66\:66f2\:7dda\:306e\
\:50be\:304d|)\n\:767a\:6563\:306e\:30b1-\:30b9", 
      DisplayFunction -> $DisplayFunction]

Show[myspdr[1], 
      PlotLabel -> "\:8718\:86db\:306e\:5de3\:8abf\:6574\:904e\:7a0b\n(|\
\:9700\:8981\:66f2\:7dda\:306e\:50be\:304d|=|\:4f9b\:7d66\:66f2\:7dda\:306e\
\:50be\:304d|)\n\:5468\:56de\:306e\:30b1-\:30b9", 
      DisplayFunction -> $DisplayFunction]

Show[myspdr[0.5], 
      PlotLabel -> "\:8718\:86db\:306e\:5de3\:8abf\:6574\:904e\:7a0b\n(|\
\:9700\:8981\:66f2\:7dda\:306e\:50be\:304d|<|\:4f9b\:7d66\:66f2\:7dda\:306e\
\:50be\:304d|)\n\:53ce\:675f\:306e\:30b1-\:30b9", 
      DisplayFunction -> $DisplayFunction]

\(Table[
      Show[myspdr[x], 
        PlotLabel -> {"蜘蛛の巣調整過程 発散のケ-ス b=", x}, 
        DisplayFunction -> $DisplayFunction], {x, 1.0, 1.5, 
        0.05}]\)

\(Table[
      Show[myspdr[x], 
        PlotLabel -> {"蜘蛛の巣調整過程 収束のケ-ス b=", x}, 
        DisplayFunction -> $DisplayFunction], {x, 1.0, 
        0.5, \(-0.05\)}]\)