The Population Dynamics And Survival Strategy Of Wild Chinese Alligator

Chinese Alligator (Alligator sinensis) belongs to Reptilia, Crocodylia, Alligoridae.lt only distributes in China.Now it is the first class protected wild animal in China.Historically Chinese Alligator widely distributed in Yangtze River valley and Yellow River valley.With the changing of climate and human influence its wild population declined dramatically.Till 1983, only about 500 individuals survived in some isolated sites of middle and lower reaches of Yangtze River (South Anhui Province and Northwest area of Zhejiang Province).The wild population is on the very edge of extinction.Because of the lacking on Chinese Alligator's biological information, the recovery of its wild population encountered great obstacle.The key to save the wild Chinese Alligator is to know the breeding mechanism of the remaining wild population and its survival strategy under such a serious human pressure.In six years (1998-2003), the author conducted a embedded research on the population and habitat status of wild Chinese Alligator using questionnaire survey, spotlight night counting; soil and water quality analysis.From 1999-2003, the environmental data of 40 burrows and 5 breeding nests were collected; the influence of the temperature on the natural hatch was studied by using HOBO automatic thermometer.At the same time, the interactions between air temperature and natural burrow temperature or manual burrow temperature were also studied.In April-November, 2003, a preliminary study on the home range of Chinese Alligator was conducted by radio tracking 3 released captive Chinese Alligator.From 2000-2003, the feasibility of reintroducing Chinese Alligator at Dongtan wetland,The results of these works are as below:1. A field survey conducted in the area inside and adjacent to Anhui Chinese Alligator National Nature Reserve shows that the wild population of Chinese Alligator which consists of about 120 individuals mainly distributes in Anhui Chinese Alligator National Reserve.lt has been divided into, at least, 23 isolated local populations.After a dramatic decline since 1950s' (from 5 000-6 000 individuals down to 120 individuals), since 1998 till now the wild population remains stable.The reproduction potentials of these populations are very low due to improper age structures.The main factors threatening the wild population are different in different periods.From 1950-1990, habitat destruction, hunting were the main factor .Now the main factor is habitat deficient.Though pollution, natural calamity, low reproduction show no direct threat now, they may still pose serious threats in the future.It seems that the drought has no remarkable influence on the survival of alligator.2. Now the wild alligator inhabit at three types of habitat: 1st type-remnants wetland; 2nd type-the intermediate zone, 3rd type-hills mountain region.The wild population mainly distributes in 1st and 2nd type habitat (each is 38.46%), the areas are 17.38hm2 and 19.03 hm2.Only 23.08% of the whole population distributes in 3rd type habitat (22.04 hm2).The habitat is heavily overlapped with human activity areas.Habitat deficient is the most important obstacle to the survival of wild alligator.3.The analysis on the 200 data from 40 burrows inside Anhui Chinese Alligator National Nature Reserve shows the main factors of burrow selection are the height between burrow entrance and water surface (87.5% of all burrows <0.5m); the distance between burrow entrance and water area (85% of all burrows <5m); the direction of burrow entrance (72.5% of all burrows: north); the plant cover rate (72.5% of all burrows <70%), the distance between burrow and human inhabited area (42.5% of all burrows <100m).The main factors causing the abandon of the burrow are water and habitat quality.4. The study on the environment of 4 nests shows the preliminary estimated conditions of a good wild nest: plant cover rate>60%, the distance from water area<20m, good concealment (Exp.island in the middle of a pond, dam between two ponds), and flatness, far from human disturbance...