Monkey conflict data
We obtained social conflict data ofNorthern China Rhesus Monkeys from Hongshan Forest Zoo of Nanjing, China. Nanjing (31° 14′–32° 37′ N, 118° 22′–119° 14′ E) is located in the central region of the lower Yangtze River and southwest of Jiangsu Province. It is an important national gateway city for the development of the central and western regions in the Yangtze River Delta, with an area of 6587 km2 covering a population of more than 8 Million. Average annual temperature is about 15.4 °C. Annual precipitation is 1106 mm, 60% of which occurs from Jun to Sep.
There are about 90 monkeys in the Hongshan Zoo in 2017, about 35 adults, 20 sub-adults and 35 juveniles or new-borns. The round monkey park was located in the central part of the zoo, with an area of about 2000 m2. Although a thick and 3-m high glass wall has been built to prevent artificial feedings, visitors sometimes throw food into the monkey park, causing a social conflict due to the food competition. Usually the zookeeper feeds these monkeys twice a day at about 9:30 am and 3:30 pm respectively.
We established a monitoring camera web (Haikang DS-7104N-SN/P) covering the monkey park in September 2016 and video-recorded the whole population since then. We defined social conflicts of monkeys as aggressive or fighting behaviors between individuals, including chasing (one chases another until it escapes), wrestling (one grapples and wrestles with another, until one escapes or gives up), biting (one opens its mouth and bites or tries to bites another), scratching (One scratches or scrapes another using its hands), threating (One warns or threats another through calling or behavioural display), etc. The age of participants and the occurrence time were recorded for each aggression46. We considered a conflict ends if there is no continuation within 10 s after the aggression. Since these monkeys are inactive during the night, we only recorded their diurnal aggressive behaviors from 6:30 till 18:30 and then summed the fights as daily social conflicts. One-year round data were collected from Mar 2017 to Feb 2018.
Air Quality Index
We obtained Air Quality Index (AQI) data of Nanjing from the Data Centre of the Ministry of Environmental Protection of the People’s Republic of China (MEP, http://datacenter.mep.gov.cn/)17. Based on established criteria (GB3095-2012). AQI is calculated for six major air pollutants separately: particle matter < 10 microns in diameter (PM10, μg/m3), particle matter < 2.5 microns in diameter (PM2.5, μg/m3), ground-level ozone (O3, μg/m3) level, carbon monoxide (CO, mg/m3) level, sulphur dioxide (SO2, μg/m3) level, and nitrogen dioxide (NO2, μg/m3) level. An individual score is assigned to the level of each pollutant and the final AQI is the highest of those 6 scores. AQI values range from 0 to 500, and can be classified into six categories (Good: 0–50, Moderate: 51–100, Unhealthy for Sensitive Groups: 101–150, Unhealthy: 151–200, Very Unhealthy: 200–300, Hazardous: 301–500).
Meteorological variables
We obtained meteorological data from a public weather website (http://www.tianqihoubao.com/). We collated data of weather conditions, wind force and ground air temperature (°C). Based on these data, we defined the weather conditions as: sunny or cloudy; light rain or overcast; and heavy rain or snow. Wind force was classified into two categories: breezy or windy. According to the sample distribution, we defined breezy as wind force less than 3rd level (China wind level standard, wind speed less than 5.4 m per sec), and windy as wind force more than 3rd level. We categorized temperature into 7 levels: < 10 °C, 10–14 °C, 15–19 °C, 20–24 °C, 25–29 °C, 30–34 °C, and ≥ 35 °C. We did not deal temperature as a continuous variable since many similar studies in social science categorized the temperature24,47. To simplify the possible effect of week days, we categorized the dates into two types: weekdays, and weekends or statutory holidays (including Spring Festival, Ching Ming Festival, Labor Day, Dragon Boat Festival, Mid-Autumn Festival, National Day, New Year’s Day).
Data analysis
Many social and environmental factors can affect social conflicts18,19,22,31, but for a given population like Hongshan monkeys, social conflict can be considered as an independent variable to a certain extent that responds to the real-time environmental factors. There might be an effect of time series on the occurrence of social conflict18,24, such as day of week, date of month, statutory holidays However, this time series factor may play a role in studies of human behavior, psychology or sociology, but not in other animals, because obviously other animals did not have the time conception of humans, and should not be affected by this time factor. But they can feel if there are more visitors (and therefore more supplemental foods and more human disturbance) on holidays. We actually found a positive correlation between the time factor (weekday/holiday) and daily visitor numbers (r > 0.6), thus we replaced time factor with daily visitor numbers. So in our general linear model, we included 5 independent variables: weather (Sunny or Cloudy, Overcast or Light Rain, Heavy Rain or Snow), wind force (Breezy that wind speed less than 5.4 m per sec, Windy that wind speed more than 5.4 m per sec), temperature (7 levels (< 10 °C, 10–14 °C, 15–19 °C, 20–24 °C, 25–29 °C, 30–34 °C, ≥ 35 °C), air quality indexes (Continuous variable) and visitor numbers (Continuous variable). Another thing that we were caring was that the fighting behavior may be affected by the environmental factors, especially the temperature and AQI that happening prior to the fight occurring, so we established a one day lag regression model including the weather, wind force, holidays, temperature 1 day lag, and AQI 1 day lag as fixed factors. We did not find a significant collinearity among these factors (VIF < 2), and so we kept all the factors in the models. We also tried the models using temperature as a continuous variable and even with a quadratic function of temperature, but these models explained much less variance (less than 14%) than our current models, so we decided using categorized temperature in our final analysis. Wind force has no effect in both models (P > 0.9), so we removed the wind force from the final models.
We calculated partial η2 to identify the relative importance of each factor after controlling for other factors. As suggested, values of partial η2 with 0.01, 0.06 and 0.14 indicate small, medium, or large effects for any measure of the proportion of variance explained48,49. All analyses were conducted with SPSS 18.0, significant level was set at 0.05, and statistical values were shown as mean ± SE.
Ethic information
This is an observational study, we did not take any measures on these animals except video recordings.
Source: Ecology - nature.com
