Test the Following Series for Convergence or Divergence $\sum _ { n = 1 } ^ { \infty } ( - 1 ) ^ { n } \frac { n ^ { 2 } } { n ^ { 2 } + 1 }$

Test the following series for convergence or divergence: $\sum _ { n = 1 } ^ { \infty } ( - 1 ) ^ { n } \frac { n ^ { 2 } } { n ^ { 2 } + 1 }$ .