Too Many Is Too Bad: Long-Term Net Negative Effects of High Density Ungulate Populations on a Dominant Mediterranean Shrub

摘要

Plant–animal interactions imply costs and benefits with net balance depending on interacting\udspecies and ecological context. Ungulates, in particular, confer costs (e.g., plant leaf\udconsumption, flower bud predation) and benefits (e.g., plant overcompensation, seed dispersal)\udto plants. Magnitude of costs and benefits may be altered by habitat management or\udecological conditions favoring high density ungulate populations. Little is known however\udon whether plant costs or benefits predominate over the years, or the long-term outcomes\udof plant-animal interactions in habitat types sustaining high density ungulate populations.\udWe investigated how high density ungulate populations alter plant costs and benefits by\udquantifying ungulate long-term effects on the shrub Cistus ladanifer (Cistaceae) individual\udsize, seed weight and number, seed bank, and population density, through a 12-year ungulate\udexclusion experiment in a Mediterranean scrubland. We monitored plant size and flower\udbuds in plants exposed or protected from ungulates and number of developed capsules and\udseeds consumed (potential seed dispersal) by ungulates during three reproductive seasons.\udWe found that ungulates negatively affected shrub size and led to a dramatically\uddecline of shrub reproductive structures and seed production, affecting the plant reproductive\udcycle. Number of buds was 27 times higher and number of developed seed 5 times\udhigher in ungulate-excluded as compared to ungulate-exposed plots. After 9 years of ungulate\udexclusion, the C. ladanifer seed bank was 2.6 times higher in ungulate-excluded plots.\udThe population density of C. ladanifer was 4 times higher in ungulate-excluded plots. Our\udlong-term experiment showed that high density ungulate populations can alter plant-animal\udinteractions by reducing plant benefits and increasing plant costs.