Recruitment Of Other Species Research Articles

Effects of Macroalgal Dynamics on Recruitment of a Temperate Reef Fish

Spatial and temporal variation in the recruitment of dispersive life stages can strongly affect the distribution, dynamics, structure, and gene flow of local populations. I investigated the causes of variable larval recruitment to populations of a temperate reef fish, the kelp bass (Paralabrax clathratus). Spatial and temporal variation in the density of settlement habitat on a reef, the giant kelp (Macrocystis pyrifera), explained much of the variation in recruitment of kelp bass. Although recruitment was positively related to Macrocystis density, the relationship was asymptotic at high plant densities, indicating that kelp bass recruitment saturates at intermediate densities of Macrocystis (°100—130 stipes/30 m2). Field experiments demonstrated causation between Macrocystis density and kelp bass recruitment and indicated that kelp bass recruitment was linearly related to the local abundance of kelp structure (i.e., the number and biomass of overlapping Macrocystis blades). This linear (nonasymptotic) relationship between Macrocystis blade biomass and density of fish recruits indicated that both the quantity and quality of the recruitment habitat limited larval recruitment. Structural complexity per unit length of plant (e.g., blade biomass per unit plant length) was inversely related to plant density. This relationship underlies the asymptotic relationship between structural complexity per unit reef area (the product of per—plant structural complexity and plant density) and recruit density. Thus, density—dependent constraints on blade biomass in the macroalga, rather than larval supply, better explained the general asymptotic nature of the relationship between Macrocystis and kelp bass recruitment. These results indicate that density—dependent effects on plant biomass and architecture (e.g., plant height and structural complexity), common among both macrophytes and terrestrial plants, can greatly influence the relationship between plant density and recruitment of other species. For organisms with dispersive life stages whose local recruitment is influenced by the occurrence of living habitat structure, spatial and temporal variability characteristic of such biogenic habitats can be a major source of variation in their recruitment.

Niche separation within the mobile predator guild on marine shallow soft bottoms

Segregation of coexisting predatory fish and shrimp species on marine shallow soft bottoms was studied in the Gullmar Fjord (Sweden). Here, the gobiids Pomatoschistus minutus (Pallas) and P. microps (Krayer) and the brown shrimp Crangon crangon L. are the most abundant epibenthic species close inshore. A temporary reduction in number of one of the species was balanced by an increased recruitment of other species in the guild, so that the overall density of epibenthic predators was kept at approximately the same level. Experimental validation of field results showed that segregation maintained by interspecific territoriality is an important mechanism regulating guild structure. We argue that competitive relations undoubtedly are of importance in maintaining structure of the epibenthic communities in Gullmar Fjord, but of minor importance for overall density of the guild.

The Fouling Community at Beaufort, North Carolina: A Study in Stability

The stability of natural communities can only be studied by asking, How does a local resident adult assemblage respond to the perturbations it experiences? One must measure perturbations directly and independently of the community response. One must be alert to perturbations which potentially or actually add to, as well as subtract from, the resident adult assemblage. The appropriate time scale will depend on the perturbation frequency and the community response, if any. This approach to stability is applied to the fouling community at Beaufort, North Carolina. Multiple stable points, resident assemblages resistant to recruitment (Sutherland 1974), are common and are evidence for persistence stability. However, most eventually disappear because of continued recruitment of other species, overgrowth, sloughing off, or senility. Thus there is ample evidence for instability in the community (Sutherland and Karlson 1977) especially if one compares the species composition of winter assemblages. However, with ...

Bird Activity and Seed Dispersal of a Tropical Wet Forest Tree

Feeding assemblages of birds were observed throughout a fruiting season at a Costa Rican population of the rain forest tree Casearia corymbosa in order to distinguish effective dispersal agents from visitors which used arils for food without dispersing seeds. This system is of special interest because the tree fruits during an annual period of fruit scarcity in a forest characterized by high proportions of animal—dispersed plants and obligate frugivores. Results show that the Masked Tityra (Tityra semifasciata) is an effective dispersal agent of seeds of this tree because it: (1) regurgitates viable seeds, (2) is a common and regular visitor throughout the season, (3) has high feeding rates, (4) removes seeds from the vicinity of the parent tree before processing them, and (5) depends on this rather than other plants fruiting at the same time. Twenty—one other visitors were deficient dispersers, although some depended heavily on fruit of this tree for food. Two parrots (Amazona autumnalis and Amazona farinosa) preclude dispersal by stripping arils with their bills and dropping all seeds in situ. Fourteen species are occasional visitors. Five visitors (Ramphastos sulfuratus, Ramphastos swainsonii, Pteroglossus torquatus, Myiozetetes similis, and Myiozetetes grandensis) process seeds undamaged and sometimes numerically abundant, but are absent part of the season and tend to regurgitate seeds in situ. Because fruiting activity of this tree occurs during annual scarcity, it represents a pivotal species in the community. Three obligate frugivores, including one effective disperser and two fruit thieves, depend almost entirely on it for food periods of 2—6 wk. I hypothesize that extinction of this plant at this site would lead to disappearance of these birds, and would almost certainly depress recruitment of other species of trees for which they serve as dispersal agents at other times of the year.