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preface
The gradual fragmentation of forest habitats leads to an increase in marginal areas, which may differ in structure and quality from the interior of the forest.
This time, we will mainly explore whether the habitat structure of the nocturnal and highly arboreal Sahamalaza frolicking lemurs is affected by the forest edge effect.
Generation of forest edge areas
Tropical forests are often cut down for agricultural purposes, breaking down contiguous large areas of habitat into increasingly isolated fragments.
Continued fragmentation leads to an increase in forest margin areas that differ from forest interiors in terms of abiotic (i.e., temperature, humidity, sun exposure) and biological (i.e., vegetation composition) variables.
This, in turn, affects the species composition and relative abundance of the animal communities in the debris, with some species avoiding marginal areas and others increasing in population density as the resources required change.
Although marginal areas are often seen as lower-quality habitats, they are becoming an increasing part of the range of forest-dependent species, especially hibernating species or highly fruit-eating species.
It is often attracted to the edge of the forest because of the increased number of insects and leaf quality in these areas.
Since most primates now live within 1 km of the edge of the forest. Understanding the impact of marginal regions on primate ecology and behavior is therefore critical.
While some primate species can tolerate forest edges, other primate species change their activity patterns, feeding behaviors, and group cohesion when they are at the forest edge compared to forest interiors.
Primates may also face nutritional stress due to inadequate food supplies at the forest edge.
This is especially true for carnivores, but may also be applicable to species that employ other dietary strategies. For example, maned howler monkeys feed more on stems and fewer on leaves, and have a greater number of tree families at the edge of forests compared to forest interiors.
In contrast, the swamp macaque population, which lives in a forest area divided by a main road, increases the distance they walk each day and preferentially feeds on the edge of the forest near the road.
Behavioral changes in response to changes in habitat structure and quality may have long-term effects on population health.
How forest edges affect lemur populations
As more primates are threatened with extinction, it is becoming increasingly important to understand the effects of habitat change and primates to respond to them in order to effectively mitigate any negative impacts that forest edges may have on primates.
As Madagascar's forests continue to fragment, understanding how forest edges affect lemur populations is critical.
As of 2007, up to 80% of Madagascar has little connectivity between debris within 1 km of the remaining forest, and further fragmentation continues.
Marginal-related microclimate change penetrates forests up to 1 km, crosses forest types, and affects plant and animal responses up to 300 m.
The spatial extent of marginal impacts makes it possible that at present, only a small proportion of Madagascar's forests may be unaffected.
While resource distribution may be favorable, the constant invasion of populations may put additional pressure on lemurs to avoid marginal areas.
Lepilemur is a small sport lemur (600–1200 g) and a nocturnal and highly arboreal primate found throughout Madagascar.
All sports lemur species are listed as threatened by the IUCN and have occurred, with measurable genetic consequences of local extinction and habitat fragmentation.
Although the genus persists even in small fragments, population size correlates with forest fragment size, with fewer individuals in smaller fragments.
Active lemurs are considered total leafeaters, and forest margins provide a valuable resource for leafeaters because increased solar radiation increases the ratio of protein to fiber in the leaves and increases leaf yield.
However, playful lemurs travel mainly by climbing and jumping, for which larger trees are needed – something unusual at the edge of a forest.
Although previous studies have shown that some sports lemur species appear to be more susceptible to the overall size and degree of degradation of forest debris than the marginal effect itself.
There is no information on whether they adjusted their behavior to adapt to the microclimate at the forest edge, or changes in vegetation structure.
Changes in lemur habitat
If playful lemurs persist in marginal areas, their behavior and ecology need to be studied to determine whether individuals living in marginal areas behave differently from individuals living in core forests, especially in small forest fragments.
We studied a group of playful lemurs inhabiting a small forest fragment (about 50 hectares) of the Ankarafa forest on the Sahamalaza Peninsula in northwestern Madagascar.
The fragment consists mostly of regenerated (but degraded) forests, and human activities such as logging, fire, and hunting, although prohibited, still occasionally occur throughout the forest.
The purpose of this study is to investigate whether the forest edge, suitability for Ankarafa sports lemur habitat, or if living at the edge, potential changes in its resources or differences in microclimate, incur potential fitness costs, reflected in changes in activity budgets and household size size.
We hypothesize that if marginal effects play a role in the Ankarafa forest, there will be a significant edge-to-interior gradient in the microclimate.
If this is the case, we predict that forest debris will show higher temperatures and lower humidity to the forest edge, as has been recorded in other forests.
We also hypothesize that if there are significant changes along the microclimate gradient, these changes will be reflected in the canopy cover and vegetation composition from the edge to the interior.
Here, we predict that vegetation changes compared to the edges will be reflected in the interior of the forest, with more large trees and a more enclosed canopy.
Furthermore, we hypothesize if the microhabitat at the edge of the forest is different from the forest interior of the Ankarafa forest. And if this negatively affects the Sahamalaza movement on monkeys, then individuals living in marginal areas will show differences in activity budgets and range sizes. Inside the forest.
The depth of the marginal effect - microclimate
To determine the extent to which the edge effect penetrates forest debris, we set up five parallel cross-sections. The cross-section is perpendicular to the edges, 400 m long, covering about half of the width of the fragment.
The distance between them is at least 50 m, and we chose a non-random starting point for the cross-section, since they can enter the forest fragment.
However, clearing vegetation to make forest debris easier to access is considered counterproductive in terms of conservation in this study. We mark cross-sectional points with marking tape at 10-meter intervals and remove all markers at the end of the data collection period.
Marginal effect depth – assessment of vegetation structure
To investigate structural changes in vegetation from the edge to the core, we set structural changes in vegetation from the edge to the core, we set points at 0-, 10-, 20-, 40-, 60-, 100-, 150-, 200-m, and 250 m.
The plot size is 20 m × 5 m, with long sides parallel to the edge of the fragment. Due to a severely degraded patch in the core area of the forest between the 300-meter and 300-meter points of cross-section 1, we placed the vegetation plot only at the 250-meter point.
These distances are comparable to studies that detect edge-related changes in boreal and tropical forests. We made the following measurements: the total number of all trees over 2.5 m in height, and the total number of breast diameters and all bamboo stems, which we may identify as genus or species level.
We excluded all plants that could not at least be identified, at the genus level (n = 18) from the following diversity analysis.
For all data, we treat all trees with the same vernacular name as the same species if we cannot identify species from the vernacular name.
If we can only identify trees at the genus level, and the vernacular names are different from species in the same genus, we treat them as separate species, we measured the middle canopy height using a laser rangefinder.
We chose the middle height of the canopy instead of the height as the measurement, as canopies often have impenetrable properties, making it difficult to measure the overall height of the tree. We then estimate the tree height using mid-canopy measurements.
The depth of the marginal effect - microclimate
Piecewise linear regression resulted in significant breakpoints in microclimate data from the edge to the interior of the forest: temperature data showed estimated breakpoints of 148.1 ± SE 15.1 m (± standard error) for rainy season and 123.9 ± SE 9.6 m for dry season.
Humidity breakpoints were 145.8 ± 10.8 m in the rainy season and 165.5 ± SE 18.8 m in the dry season.
Light intensity and canopy cover show breakpoints at 10 ± SE 1.2 m in all seasons, and the average values of temperature and humidity differ significantly before and after the calculated breakpoints, in the rainy season, the temperature decreases after the breakpoint, while in the dry season the temperature increases after the breakpoint while humidity decreases.
As a result, marginal effect areas (areas from the edge of the forest to the breakpoint) differ significantly from the forest core in terms of microclimate. The affected area covers 70% of the forest debris studied.
The author's opinion
Our results suggest that Lepilemur sahamalaza is a widely distributed genus capable of surviving on forest edges without significant behavioral effects, but there is still a need to further understand how fringe effects affect arboreal primates in the Anthropocene.
The primary objective of our research is to understand microclimate and vegetation responses at a small forest edge, and studying abiotic and biotic marginal effects should be the baseline for any study of primate responses, rather than arbitrarily defining the forest edge.
We found that the microclimate at 165 meters did show a significant marginal effect, a result that was not obvious only in terms of vegetation structure and could affect other primates in the same forest.
We found no measurable behavioral responses, adding to the body of knowledge about how small, leaf-eating primates respond to forest edges.
The margins will most likely not affect these species, and as long as their ecological needs are met, they can exist in the form of small fragments, suggesting that even small forest fragments are valuable conservation targets.
This provides us with important information on land and species management, as the presence/absence of forest margins can affect population density estimates and help identify potential conflict points between humans and non-human primates.
However, in addition to understanding whether primates can tolerate forest edges, more in-depth research into behavioral, ecological, and physiological responses is important to understand the potential trade-offs and factors that affect primate health in the long term.
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