Baldi, Andras. 2008. Habitat heterogeneity overrides the species-area relationship. Journal of Biogeography35(4): 675-681.
Blog author: Maria Goller
Author bio:
> Received his PhD in 1996 in environmental sciences at L. Eötvös University
> Director of the Centre for Ecological Research at the Hungarian Academy of Sciences
> Broad focus is biodiversity (mainly bird communities)
> More specifically, he is interested in how human land use shapes ecosystem services (pollination and soil decomposition) and how these affect biodiversity
> Was a partner on the Liberation project which investigated farmland biodiversity and ecosystem services.
Summary/Main Points
Background:
> Many explanations for the species-area relationship fail to incorporate habitat heterogeneity
> Random model: just because larger area => more individuals => more species
> Equilibrium model: based on immigration and extinction, and isolation of habitat patches
> But habitat heterogeneity is potentially extremely important
Assumptions:
> Larger reserves conserve more species
> Area is more important than heterogeneity of habitat
Main question:
> Baldi wanted to directly compare the effects of area and heterogeneity – does the species-area relationship still hold if larger areas have lower heterogeneity?
Methods:
Data:
> Study site in Hungary – 16 reserves
> Field surveys for all animal species from 1977 to 1980
> Focused on arthropods for analysis
Methods:
> Used observations for various arthropod families
> Graphed species-area curves and looked at the relationship between habitat type density (heterogeneity) and species density (richness)
Results:
> Heterogeneity was positively correlated with number of species
> Small patches were more heterogeneous than larger patches
> Richer habitat (soil, etc…) => greater productivity
> Some families/groups of taxa greatly influenced by very small-scale changes (such as in soil) that are not related to area
> Certain taxa with good dispersal have a strong positive species-area relationship
Conclusions:
> Protect areas with greater heterogeneity
> But also keep creating large preserves – these often have specialized species that are only found there, and not in small reserves, even if small reserves have a greater total number of species
> Productivity is also an important factor
Questions:
> How useful do you think it is to spend years doing surveys to compare reserves?
> What other factors – aside from heterogeneity and productivity – could affect the species-area relationship?
> While conserving multiple small reserves may be more beneficial to conserving biodiversity, is it actually feasible in the long run?
I liked that this paper broke down the species found in each area by taxonomic groups and demonstrated the pattern of species-area for each. The study biased in that they are using only land set aside for and mentioned larger patches having lower quality soil. This suggests lower quality soil would not support as many species of plants and that reducing the number of insect species, etc. I would also be curious to know if any of the preserves were manipulated in any way by planting native plants or removal of invasives by park rangers or agencies. However, looking at individual taxonomic groups could help identify a bias impacting a single group if the history of the preserve is considered.
ReplyDeleteI'm not sure if I'm supposed to comment on my own blog post, but here goes... What I most appreciated about this paper is that it brings up other drivers of the species-area relationship (such as productivity), and doesn't simply lump all species together. Of the papers we've read so far, this one does the best job of emphasizing the importance of using local ecology to understand the species-area relationship.
ReplyDeleteI agree with Alex that it was kind of odd that they chose larger reserves of unproductive land, and smaller reserves of fertile land. I imagine that would skew results a fair amount.
ReplyDeleteWhile I agree with the other comments that the fact that the large areas were less productive, I think that's outside of the author's and other contributing scientists' control. The table describing the 16 reserves show that the larger reserves are grasslands, while the smaller ones are more heavily forested. I think this has to do with the way the reserves have been previously created, and not arbitrary research areas. As Maria commented, I also appreciate that this paper goes deeper than the initial size-species richness relationship that the other models hone into. The previous models remained at a surficial level with their understanding, while this paper attempts to go deeper to understand what is causing the richness gradient across size changes. The productivity of an area may be one such factor, however there would need to be more studies completed to decipher all the underlying factors that create species richness relationships. I also appreciate the nod to "generalist" species skewing the models of species richness-area relationships.
ReplyDeleteConserving multiple small reserves can be feasible in the long run if the reserves are arranged in a way to maximize the immigration rate between the populations. Like we talked about in the last class, if the reserves are close to each other, we can have protective linking corridors between the reserves to help increase immigration rate.
ReplyDeleteI also liked how this paper actually measured how the different habitats enclosed to an area can be the drivers of species richness and not just the area per se. I think it is logical to think that a bigger area would most probably enclose a much amount of different habitats than a small one. But the idea that, nowadays, the most productive and variable areas are reduced in most places, is something that was not taken into consideration in the papers we have analyzed so far.
ReplyDeleteAs for the last question Maria asked, I think both large and small reserves would be needed in the future, both of them should have different habitats enclosed though. Some animals would be specific to small areas, while others (such as mammals and birds) might need a larger area to roam and feed. Also, as the Climate Change is upon us, larger areas, I think, would offer more chances to animals to adapt or move around. So I don't think just small areas are feasible in the future.
Another thing I liked was that they used arthropods for this study. They are very abundant and can be found in many different habitats, so I think that if they were able to get this conclusions with these animals, it is very robust. Also, that not all of the arthropods showed a significant trend in this study was very appealing to me, especially regarding spiders. I would have liked to know if they included web-building spiders as well as active hunting spiders. They mentioned a negative yet not significant trend concerning the diversity of this group related to area, and therefore, less habitat heterogeneity. And considering spiders have a good dispersal ability too, I wonder: was that trend due to the loss of substrates for web building? was it because of the loss of ground dwelling spiders? would that trend be significant if spiders are divided in those two ecological groups?
I thought they did a good job castin doubt on the species-area hypothesis, but don’t think they did themselves justice when promoting their heterogeneity hypothesis. It logically makes sense, but because of the difference in productivity and size, they can only look at one or the other. Perhaps it would have helped to also look at large reserves of forest and small reserves of grassland? Or multiple types of grassland preserves etc. Of course you can only work with the available data, and I think they did a good job limited by the Hungarian reserve system.
ReplyDeletePreserving a large area is needed (just in case, if we miscalculate some system that has not been detected and crucial to other systems) but for the conserving biodiversity, we need to systematically approach to the conservation process. I think that we need to prioritize the conservation levels by small patches with corridors first (consider at least: endemic species, ecosystem, functional groups, heterogeneity and etc). Then extend the buffer area as much as we can. Also, every time when we come up with a scientific reasoning to protect or conserve something, an action plan has to be followed with multiple different levels (know your enemy=have alternative options for the approach).
ReplyDeleteThe larger the area is better because of the following reasons.
1. We usually do a preliminary observation of a system and then make a study design do the research to figure out some patterns. However, most of the time that the majority of the small patterns cannot represent a new pattern that will take over after some time. Therefore, it is safe to have an extra area for the future when the system shifts to a new setting.
2. We have to be certainly ready for the future challenges to make something happen otherwise the idea can be destroyed easily or evaporate in the air with a very little effort by someone or even time. We don't want to complicate the process too much that confuses people so it is just better to conserve large area as possible and work on the protection levels and categorize them.
3. We might only have one shot to do this kind of mega approach because of our opponents are too great (political challenge, human beliefs (religion), media (wrong group), money (greedy selfishness), uneducated justification on natural resources, time, and climate change=infectious disease! So bigger land it better in the beginning. The habitat heterogeneity paper is great. We need more of these kind of support to move forward.
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ReplyDeleteBefore taking any ecological class my process of thinking was the random process hypothesis, I just assumed that larger areas would have more organisms occupying the space; but now that I know that’s not the case it’s cool learning about the other theories. The author does a good job of pointing out the flaws of the species-area hypothesis, but I don’t think he does a good job of proving the habitat heterogeneity hypothesis or at least comparing the relative contribution of area vs. heterogeneity to species richness. I believe this is due to the way he set up his experiment.
ReplyDeleteI´m still thinking about how generalizable are the results of this study given that the comparison was done over two very different kinds of general habitats. I think it is possible that productivity alone can explain the pattern. Of course, even if that is true, this would still support the idea that area is not always the most important factor, but my question is what would happened with more similar land covers.
ReplyDelete