Effects of Short-term Climate Variation on a Long-lived Frog
We assessed the effects of short-term, naturally oscillating, climate variation on Crawfish Frogs (
Lithobates areolatus
), a long-lived member of the family Ranidae. Our data demonstrate 1) no relationship between drought conditions (high temperatures, low precipitation) and either breeding onset (phenological shifts) or breeding peaks; 2) no relationship between drought and adult survivorship (although there were trends; both females and males experienced their lowest survivorship estimates during the wettest years, a contrary finding related to crayfish burrow occupancy); 3) a strong relationship between drought and breeding duration; 4) a strong, inverse correlation between drought and body condition in both females and males; and as a result, 5) a relationship between drought and fecundity with potentially serious demographic consequences. If we assume that the mass of an individual egg remains constant under various climate conditions—i.e., that a reduction in egg mass equals a reduction in egg number not egg size—the effects of drought may be severe. Our estimated average difference of 2,647 eggs produced by individual females between wet and dry years translates into an estimated loss of 137 breeding adults recruited into this population following droughts, compared with wet year recruitment.
Female Crawfish Frog captures at breeding wetlands in 2009–2015 at Hillenbrand Fish and Wildlife Area-West, Greene County, Indiana, USA. Captures are divided into new frogs and recaptures. “Recaptures” indicate frogs that had been previously captured at any time during this study. We indicate the percentage of all captures that were recaptures for each year.
Drought prior to breeding influenced Crawfish Frog body condition (scaled mass index; SMI) of both (A) gravid females (n = 356) and (B) males (n = 730). We calculated SMI values for each frog entering breeding wetlands in 2009–2015 at Hillenbrand Fish and Wildlife Area-West, Greene County, Indiana, USA. Frog 53 was the only adult female captured every year of this study; her annual SMI values are plotted as yellow circles for comparison with the means of all captured frogs.
Crawfish Frog (Lithobates areolatus) breeding at Hillenbrand Fish and Wildlife Area-West in Greene County, Indiana, USA, 2009–2015. We included the first annual capture of frogs entering drift fenced wetlands (n = 2) and trapped in non-fenced wetlands (n = 4). Year markers indicate the peak captures for each year.
Drought was not correlated with Crawfish Frog breeding start date (A; r2 = 0.36, P = 0.15) and peak date (B; r2 = 0.11, P = 0.47), but was correlated with end date (C; r2 = 0.93, P < 0.001) and breeding duration (D; r2 = 0.98, P < 0.001) in 2009–2015 at Hillenbrand Fish and Wildlife Area-West, Greene County, Indiana, USA.
Drought prior to the breeding season was not correlated with annual survival in either Crawfish Frog females (A; r2 = 0.45, P = 0.15) or males (B; r2 = 0.26, P = 0.30) at Hillenbrand Fish and Wildlife Area-West (Greene County, Indiana, USA) in 2009–2015. Wet years appear to have had a negative effect on survivorship (see circled values), but this result was not significant.
Drought was correlated with a decrease in both female Crawfish Frog body condition upon arrival at breeding wetlands (A; r2 = 0.57, P = 0.048) and egg mass (i.e., female gravid–spent body condition (B; r2 = 0.81, P = 0.038) at Hillenbrand Fish and Wildlife Area-West, Greene County, Indiana, USA.
Contributor Notes
Associate Editor: J. Kerby.