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Desert animals and plants interact in ways that have strongly influenced their respective evolutionary trajectories. This chapter begins with herbivory because of its widespread impacts, many of which are presumed to be negative. It then moves on to some other important aspects of desert plant—animal interactions, with a focus on pollination and seed dispersal. Of the various forms of pollination, the chapter will explore the yucca moth-yucca and senita moth-senita cactus mutualisms. With regard to the role of animals in seed predation and seed dispersal, it will consider the effects of small mammals and ants on seed abundance, and the role of large mammals in dispersing the seeds of keystone Acacia species. This selection of examples illustrates how the relatively simple nature of the desert environment has given biologists unique insights into the importance of plant—animal interactions for ecosystem function.

This chapter focuses on changes in animal diversity and composition during forest regeneration and how these changes are linked to interactions between plants and animals. Recovery of animal communities is closely linked to the recovery of plant diversity. Species composition of animal taxa recovers slowly due to the gradual influx of old-growth specialists. Non-flying taxa, rare species, endemic species, and taxa with specialized dietary or nesting requirements are less likely to colonize isolated and small areas of regenerating forests during early stages. Early successional plant species support higher densities of herbivores and sustain greater amounts of herbivory than late successional species. Seed dispersal by frugivores increases during forest regeneration, along with increases in seed size and the proportion of shade-tolerant species. Dispersal limitation and seed predation decrease rates of succession, particularly in isolated pasture sites. Over 90% of the flowering plant species in tropical forests rely on animals for pollination.

The soil seed bank refers to a reservoir of viable seeds present on the soil surface or buried in the soil. It has the potential to augment or replace adult plants. Such reservoirs have regular inputs and outputs. Outputs are losses of seeds by germination, predation or other causes, while inputs include dispersal of fresh seeds from local sources and immigration from distant sources (Harper 1977). Since sand dunes are dynamic because of erosion, re-arrangement or burial by wind and wave action, efforts to find seed banks have largely been unsuccessful. Following dispersal, seeds accumulate in depressions, in the lee of plants, on sand surfaces, on the base of lee slopes and on the driftline. These seeds are often buried by varying amounts of sand. Buried seeds may subsequently be re-exposed or possibly lost over time. However, the existence of a seed bank can not be denied. Plant species may maintain a transient or a persistent seed bank depending on the longevity of seeds. In species with transient seed banks, all seeds germinate or are lost to other agencies and none is carried over to more than one year. In contrast, in species with a persistent seed bank at least some seeds live for more than one year. The four types of seed banks described by Thompson and Grime (1979) provide useful categories for discussion of coastal seed bank dynamics of different species. Type I species possess a transient seed bank after the maturation and dispersal of their seeds in spring that remain in the seed bank during summer until they germinate in autumn. Type II species possess a transient seed bank during winter but all seeds germinate and colonize vegetation gaps in early spring. Seeds of both types are often but not always dormant and dormancy is usually broken by high temperatures in type I and low temperature in type II. Type III species are annual and perennial herbs in which a certain proportion of seeds enters the persistent seed bank each year, while the remainder germinate soon after dispersal, and Type IV species are annual and perennial herbs and shrubs in which most seeds enter the persistent seed bank and very few germinate after dispersal.

All who work on dipterocarps will be aware of the almost unique supra-annual reproduction of dipterocarps in the aseasonal tropics, associated with El Niño climatic events. This ‘masting’ reproductive behaviour gives rise to long periods of resource scarcity punctuated by short-lived periods of resource abundance. This is thought to drive many ecological processes in the aseasonal Asian tropics, including those affecting seedling survival, plant distributions, and population genetics. Reproductive patterns are, however, more complex than has been hitherto thought, and there is much yet to learn much about what drives reproductive patterns among dipterocarp species. The evolutionary drivers for masting behaviour among dipterocarps in insular Southeast Asia are described, as are the proximate cues that initiate masting. In the more climatically seasonal region masting gives way to more predictable annual or biannual reproductive phenologies. Pollination processes, which differ in masting and non-masting regions, are described. The chapter continues to describe fruit production and dispersal. The implications of pollination and seed dispersal processes for population genetics are evaluated, as is evidence for hybridization, apomixes, and selfing. Finally, predation of seed can be very substantial among dipterocarps, and has been proposed as a driver of masting behaviour.

Plant–animal interactions are as important in deserts as they are in any other ecosystem. Although it is likely that abiotic factors have greater influence in deserts than in other ecosystems, biotic factors are nonetheless very important. Desert plants and animals interact in ways that have strongly influenced their respective evolutionary trajectories. Interesting forms of these interactions include herbivory, pollination, seed dispersal, and seed predation. There is considerable evidence that many coevolved interactions occur in deserts, some of the most unique being between pollinators and their flowers. As with all mutualisms, there is a cost involved—if either of the species, for any reason, cannot be found at the right place at the right time, each of the species suffers reproductive failure. Regarding seed dispersal and seed predation, myrmecochory (seed dispersal by ants) is often regarded as a diffuse mutualism between a guild of plants and a guild of ants.

Human activities superimpose complexity onto spatially and temporally variable successional processes. Biotic and anthropogenic legacies of land-use transitions and forest regrowth are intricately connected through effects of landscape suitability for crop cultivation or pasture establishment; these phenomena strongly affect rates and scale of land clearing for agriculture, duration of land use, rates of agricultural abandonment, and seedling establishment following abandonment. Studies in the Old and New World tropics have documented pervasive, long-term human impacts on species composition and forest structure in tropical secondary forests. The rate, structure, and composition of forest regrowth are strongly affected by soil disturbance, residual vegetation, and proximity to seed sources. Long-term effects emerge from cascading effects of initial abundance, composition, and spatial patchiness of species that colonize abandoned agricultural areas. Thus secondary forests are particularly sensitive to human impacts and land use intensity. This chapter analyzes five major ways in which human activities influence secondary forest regeneration in Costa Rica and presumably other regions of the wet tropics: (1) remnant trees in pastures; (2) hunting and density of mammalian seed predators; (3) duration and intensity of agricultural land use; (4) landscape structure and distribution of forest patches; and (5) invasion of exotics.