Effect Of Topographic Complexity Research Articles

The effect of topographic complexity on species range size estimation and its conservation implications: a subtle oversight

The effect of topographic complexity on species range size estimation and its conservation implications: a subtle oversight

Effect of topographic complexity on species richness in the Galápagos Islands

AbstractAimThe accumulation of species through time has been proposed to have a hump‐shaped relationship on volcanic islands (highest species richness during intermediate stages of an island's lifespan). Change in topographic complexity (TC) of islands over time is assumed to follow the same relationship. However, TC can be measured in different ways and may not have the same impact across taxonomic groups. Here, we quantify TC across the Galápagos Islands and test the assumption that TC follows a predictable trajectory with island age. Subsequently, we ask whether including TC improves statistical models seeking to explain variation in species richness across islands.LocationGalápagos Archipelago, Ecuador.TaxonNative and endemic terrestrial animals and plants.MethodsFor each island, we generated eight TC indices from a 30‐m resolution digital elevation model. We tested for a relationship between each index and island age, and whether it significantly contributes to observed variation in species richness, using 11 different models for 12 taxonomic groups across the Galápagos Islands.ResultsFour TC indices were significantly negatively correlated with either island age or ontogenetic age and only one index followed the hump‐shaped relationship with age. No index consistently contributed to the variation in species richness for all taxonomic groups. However, for all 12 taxonomic groups, incorporating at least one TC index in modelling species richness improved one or more models. The most common TC index improving models was standard deviation of slope, although each index improved at least five models across all taxa. Different factors predicted taxon‐specific richness, and habitat diversity was significant for all taxa.Main conclusionsTopographic complexity is an important component influencing species richness, but its impact likely differs among taxonomic groups and different scales. Therefore, future studies should incorporate broad, multi‐dimensional measures of TC to understand the biological importance of TC.

Degrading habitats and the effect of topographic complexity on risk assessment

Topographic complexity is a key component of habitats that influences communities by modulating the interactions among individuals that drive population processes such as recruitment, competition, and predation. A broad range of disturbance agents affect biological communities indirectly through their modifications to habitat complexity. Individuals that best judge the threat of predation within their environment and can trade-off vigilance against behaviors that promote growth will be rewarded with the highest fitness. This study experimentally examined whether topographic habitat complexity affected the way a damselfish assessed predation risk using olfactory, visual, or combined cues. Fish had higher feeding rates in the low complexity environment. In a low complexity environment, damage-released olfactory cues and visual cues of predators complemented each other in the prey's assessment of risk. However, where complexity was high and visual cues obscured, prey had lower feeding rates and relied more heavily on olfactory cues for risk assessment. Overall, fish appear to be more conservative in the high complexity treatment. Low complexity promoted extremes of behavior, with higher foraging activity but a greater response to predation threats compared with the high complexity treatment. The degree of flexibility that individuals and species have in their ability to adjust the balance of senses used in risk assessment will determine the extent to which organisms will tolerate modifications to their habitat through disturbance.

The influence of habitat complexity on postrecruitment processes in a temperate reef fish population

In north-eastern New Zealand, adults of the blennioid fish Forsterygion varium Bloch et Schneider exhibited extreme differences in density among habitats of low, intermediate and high physical complexity. The age composition also differed among habitats, with complex sites supporting a greater proportion of older fish (> 1 + yr). The relative importance of recruitment and postrecruitment processes in determining these patterns was evaluated by monitoring the abundance, survival, growth and movement of two separate cohorts of juveniles in habitats of different complexity. The demographic data were based on records of individually recognised fish monitored from time of recruitment in permanent quadrats. Despite high temporal and spatial variability in the intensity and distribution of recruitment between years, adult F. varium were highly dependent on early postrecruitment mortality. Greater rates of early juvenile mortality were experienced within habitats of low complexity. The greatest impact of mortality III structuring spatial patterns occurred within the first week after settlement. Seasonal peaks in movement may have partially contributed to changes in patterns of distribution between habitats. The effects of habitat on growth were less clear, although there was a trend for growth to be better within habitats of high topographic complexity. The effect of topographic complexity on survivorship of juveniles was examined using a manipulative experiment which increased the complexity of simple habitats and reduced the complexity of heterogeneous habitats. Recruitment occurred roughly evenly across all treatments. Low complexity treatments suffered 100% mortality compared to only 13% in high complexity treatments. The demography of natural populations and the subsequent experiment suggest that differences in the abundance of adult F. varium between habitats can be attributed essentially to the early failure of juveniles to survive in large numbers in low complexity habitats.