Competition, especially for space, is another dominant interaction structuring intertidal communities. Space competition is especially fierce in rocky intertidal habitats, where habitable space is limited compared to soft-sediment habitats in which three-dimensional space is available. As seen with the previous sea star example, mussels are competitively dominant when they are not kept in check by sea star predation. Joseph Connell's research on two types of high intertidal barnacles, "Balanus balanoides", now "Semibalanus balanoides", and a "Chthamalus stellatus", showed that zonation patterns could also be set by competition between closely related organisms. In this example, "Balanus" outcompetes "Chthamalus" at lower tide heights but is unable to survive at higher tide heights. Thus, "Balanus" conforms to the intertidal ecology dogma introduced above: its lower tide height limit is set by a predatory snail and its higher tide height limit is set by climate. Similarly, "Chthamalus", which occurs in a refuge from competition (similar to the temperature refuges discussed above), has a lower tide height limit set by competition with "Balanus" and a higher tide height limit is set by climate.