Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats

Abstract

Ecosystems are structurally organized as food webs within which energy is transmitted between trophic levels and dissipated into the environment. Energy flow between two trophic levels is given by the amount of production at the lower level and by the proportion of production that is consumed, assimilated and respired at the higher level. Considerable evidence indicates that food-web structure varies predictably in different habitats, but much less is known about quantitative relationships among food web fluxes. Many of the energetic properties of herbivores in African game parks are associated with rainfall and, by inference, with net primary productivity. Respiratory costs per unit production at the consumer trophic level are higher for homeotherms than for heterotherms. Plant secondary chemicals affect herbivore dietary choices and the allocation of plant resources to those chemicals varies with resource availability. How these phenomena are translated into ecosystem fluxes is unknown. We present evidence that herbivore biomass, consumption and productivity are closely correlated with plant productivity, suggesting that the latter is a principal integrator and indicator of functional processes in food webs.

A dynamic global vegetation model for studies of the coupled atmosphere‐biosphere system

“…In ORCHIDEE, fires are the main disturbance affecting the terrestrial vegetation, but a simple parameterization of regular herbivory following McNaughton et al [1989] is included in ORCHIDEE. Other natural disturbances (such as wind throw) are not taken into account.…”

“…Following McNaughton et al [1989], the probability p a for a leaf to be eaten in 1 year is parameterized as a linear function of the annual NPP in the surroundings, N: p a = bN. With the model time step Dt of the order of one or a few days, a daily probability p d is used such that…”

“…The proportionality constant a is such that for values of N typical for tropical rain forests (1000 gC/m 2 ), the probability for a leaf to be eaten in 1 year is about 30% [McNaughton et al, 1989].…”

How does pedogenesis drive plant diversity?

“…The effects of herbivores on plant diversity can be positive, negative, or neutral, and are strongly influenced by herbivore feeding preferences, as well as by soil fertility and the productivity of the environment, which influences the ability of plants to replace lost tissue [11,31]. Herbivore biomass and the intensity of herbivory are generally affected by soil fertility and plant productivity [32], so that total herbivory is expected to decline with decreasing soil fertility during long-term pedogenesis.…”

Overcompensation in response to simulated herbivory in the perennial herb Sedum maximum

“…Herbivores can substantially affect plant populations by removing considerable amounts of plant biomass in both terrestrial (McNaughton 1989) and aquatic ecosystems (Cyr and Pace 1993). Herbivores are viewed as one of the most important selective forces in plant populations and plants have responded by evolving various defence mechanisms as adaptations against herbivory (Agrawal 2000).…”