Demography of a Collared Peccary Population in South Texas

Abstract

Population dynamics of large herbivores in semiarid environments are regulated by rainfall. Reductions in reproduction and juvenile survival are the main mechanisms of regulation. We examined population characteristics of a harvested collared peccary (Tayassu tajacu) population in South Texas to model population responses to harvest. We sampled a peccary population from 1974 to 1993, intensively collecting data from 1989 through 1993. Mean (±SE) ovulation rate (2.13 ± 0.03, n = 181) and litter size (1.89 ± 0.03, n = 151) of adults did not vary by age class (P = 0.15) or year (P = 0.94), although litter sizes of yearlings (10-21 months old) (1.71 ± 0.19, n = 7) tended (P = 0.07) to be smaller than age-class 3 adults (5-7 yr old). Minimum age at predicted primiparity was 20 months. Pregnancy rate was positively associated (χ 2 = 6.20, P = 0.013) with rainfall in the previous year. Estimated fecundity (F young/F/yr) for yearlings and adults was 0.41 and 1.0, respectively. The sex ratio of harvested animals (53.3% M, n = 1,125, P = 0.027) was skewed toward males. Lack of age-specific variation (P = 0.23) in postnatal ratios suggested that harvest was not sex specific. Age structure varied (P = 0.08) among years, with fewer old animals in 1989-93 harvests. Male and female annual survival estimates were 0.90 ± 0.17 and 0.87 ± 0.05, respectively, from 1977 to 1983 telemetry data for unharvested herds, and did not differ (P = 0.88). From life table analyses of harvested herds from 1989 to 1993, male and female annual survival estimates were 0.65 ± 0.03 and 0.73 ± 0.04, respectively, and did not differ (P = 0.13). Year, age, and reproductive status affected (P < 0.05) condition indices, namely kidney fat, total mass, and eviscerated mass. Population modeling provided an estimated rate of juvenile (≤9 months) survival of 0.32 to maintain a stationary population under the 1993 harvest rate of 20%. We propose that juvenile survival is compensatory to adult mortality attributable to hunting. Relationships among juvenile survival, density, and forage resources need field investigation to explore the effect of density-dependent survival on dynamics of peccary populations