Impacts Of Habitat Fragmentation Per Se On Population Growth, Competition And Predation With Allee Effect

Human-made habitat fragmentation has led to rapid species loss, which is one of the most severe environmental problems. However, effect of fragmentation per se, which refers to breaking apart of patches, is unclear since it is normally confounded with the effect of habitat loss. Allee effect is mostly predominant in small populations, which may reduce population growth or even reverse population growth, and may affect competition and predation, too. Studying fragmentation per se with Allee effect can provide not only better understanding of habitat fragmentation, but also have implications for biological conservation.Mathematical models were used to study the impact of fragmentation with Allee effect on population growth, competition and predation. We simulated a scenario that an intact habitat broke into two smaller patches, sum of the carrying capacity of two smaller patches equals to the carrying capacity of intact one. Impacts of fragmentation per se were estimated by comparing the difference of population growth, competition and predation between intact and fragmented habitat. The main results are:1) Fragmentation per se reduced population growth. Population growth in intact habitat was higher than the sum of smaller ones. Reduced growth rate led to smaller population size. After sufficient time, both populations in intact and fragmented habitat could reach equilibrium and the total population sizes at equilibrium are same for both intact and fragmented population. Thus fragmentation per se didn’t affect population size when populations were at equilibrium but increased the time to equilibrium. However, if the intial population size of small patch is below the Allee threshold, strong Allee effect may lead to the local extinction of this patch.2) In a competitive system, fragmentation per se influenced byAllee effect prompted the competitive exclusion, reduced stability of the system and result in collapse of the system. Fragmentation per se reduced the probability of the system reaching stable coexistence state, thus reduced stability, and the stronger the Allee effect, the lower the stability.3) Fragmentation per se increased prey population size and decreased predator population size. If the intact habitat had a stable equilibrium, as long as the carrying capacity of fragmented patch exceed the prey number that predator need to make their growth rate to be zero. The predator and prey may coexist. The predator went extinct and prey population increased to its carrying capactity if this assumption was absent. When the prey population is influenced by strong Allee effect, both species went extinct when predation was too strong. If the system had been oscillatory in intact habitat, fragmentation per se damped this oscillation, which could reduce the amplitude of oscillation or even extinguished oscillation, thus stabilized the system.We theoretically studied the impact of habitat fragmentation on the population growth, competition and predation with Allee effect. Our research provides a theoretical basis for predicting the impact of habitat fragmentation per se on species diversity and may solve the SLOSS debate whether a single large or several small reserves are better for conservation. We argue that the reserve design would be different if we have different purpose. Futhur work can be conducted by introducing other potential factors.