Depend trees can be influenced run-time (think 'eval "use Some::Weird::Module";'). What I find way more usefule that the already suggested modules is showing what is actually loaded, and from where, using Devel::TraceUse.

The chain can be a lot longer than you expect:

$ perl -d:TraceUse -MDBI -wle'my $dbh = DBI->connect ("dbi:CSV:")'
Modules used from -e:
   1.  DBI 1.616, -e line 0 [main]
   2.    Carp 1.17, DBI.pm line 159
   3.      strict 1.04, Carp.pm line 303
   4.      warnings 1.09, Carp.pm line 304
   5.      Exporter 5.64_01, Carp.pm line 11
  11.        Exporter::Heavy 5.64_01, Exporter.pm line 16
   6.    DynaLoader 1.10, DBI.pm line 160
   7.      Config, DynaLoader.pm line 25
   9.        Config_heavy.pl, Config.pm line 70
  10.          Config_git.pl, Config_heavy.pl line 1225 [Config]
   8.      AutoLoader 5.71, DynaLoader.pm line 22
  12.    Scalar::Util 1.23, DBI.pm line 290
  13.      vars 1.01, Scalar/Util.pm line 10
  14.        warnings::register 1.01, vars.pm line 7
  15.      List::Util 1.23, Scalar/Util.pm line 12
  16.        XSLoader 0.10, List/Util.pm line 26
  17.    DBD::CSV 0.31, DBI.pm line 777 (eval 3) [DBI::_firesafe]
  18.      Text::CSV_XS 0.81, DBD/CSV.pm line 54 [DBD::CSV::dr]
  19.      DBD::File 0.4, DBD/CSV.pm line 222 [DBD::CSV::Statement]
  20.        base 2.15, DBD/File.pm line 34
  21.          DBI::DBD::SqlEngine 0.03, base.pm line 91 (eval 5)
  22.            DBI::SQL::Nano 1.014600, DBI/DBD/SqlEngine.pm line 27
+ [base]
  23.              SQL::Statement 1.33, DBI/SQL/Nano.pm line 34
  24.                SQL::Parser 1.33, SQL/Statement.pm line 18
  25.                  constant 1.20, SQL/Parser.pm line 17
  26.                  Params::Util 1.03, SQL/Parser.pm line 19
  27.                    overload 1.10, Params/Util.pm line 60
  28.                Clone 0.31, SQL/Statement.pm line 25
  29.                Errno 1.11, SQL/Statement.pm line 26
  30.                sort 2.01, SQL/Statement.pm line 1100
  31.                SQL::Eval 1.33, SQL/Statement.pm line 2187 [SQL::
+Statement::TempTable]
  32.                SQL::Statement::RAM 1.33, SQL/Statement.pm line 2
+0
  33.                SQL::Statement::TermFactory 1.33, SQL/Statement.p
+m line 21
  34.                  Data::Dumper 2.128, SQL/Statement/TermFactory.p
+m line 11
  35.                    bytes 1.04, Data/Dumper.pm line 683
  36.                  SQL::Statement::Term 1.33, SQL/Statement/TermFa
+ctory.pm line 6
  37.                  SQL::Statement::Operation 1.33, SQL/Statement/T
+ermFactory.pm line 7
  38.                  SQL::Statement::Placeholder 1.33, SQL/Statement
+/TermFactory.pm line 8
  39.                  SQL::Statement::Function 1.33, SQL/Statement/Te
+rmFactory.pm line 9
  40.                    SQL::Statement::Functions 1.33, SQL/Statement
+/Function.pm line 58 [SQL::Statement::Function::UserFunc]
  41.                SQL::Statement::Util 1.33, SQL/Statement.pm line 
+22
  42.        File::Spec 3.33, DBD/File.pm line 171 [DBD::File::db]
  43.          File::Spec::Unix 3.33, File/Spec.pm line 22
  44.        Cwd 3.33, DBD/File.pm line 172 [DBD::File::db]
  45.        Tie::Hash 1.03, DBD/File.pm line 503 [DBD::File::TieMeta]
  46.        IO::File 1.14, DBD/File.pm line 741 [DBD::File::Table]
  47.          Symbol 1.07, IO/File.pm line 131
  48.          SelectSaver 1.02, IO/File.pm line 132
  49.          IO::Seekable 1.1, IO/File.pm line 133
  50.            IO::Handle 1.28, IO/Seekable.pm line 101
  51.              IO 1.25_02, IO/Handle.pm line 266
  52.            Fcntl 1.06, IO/Seekable.pm line 104
  53.        File::Basename 2.78, DBD/File.pm line 742 [DBD::File::Tab
+le]
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